Author Topic: Keithley 197A owners' corner  (Read 7723 times)

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Offline Vtile

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Keithley 197A owners' corner
« on: June 27, 2017, 06:55:26 pm »
Hello.
 
There only seems to be one or two threads on this old meter here at forums and pretty scarsely on the net. I thought some dedicated general thread on it could be handy.


The reason is ofcourse I became an owner of one of these as I just noticed a reasonable good (physically almost unused condition, even the range selectors are still matte finish) Keithley 197A 'Autoranging microvolt DMM' in a local pawnshop and couldn't walk by (after revisiting home to pick a few "precision" =0.1% 25ppm resistors and a 1.5V AA battery and test leads). The sales persons were showing symptoms of worry while I spend 15 minutes testing the scope with these "precision" references. I only kick myself that I could have twisted the price down more, he were too happy my "reasonable" discaunt of shelf-price.  >:D :P The volt-nuttery is a few digits closer (3½ to 5½).

My unit seems to load some capacitor on the frontend while unit is on DC: 200 mV range and test leads are disconnected. This seems to be the only "oddity", but since the 200mV and 2V ranges have >1Gohm input impedance I assume this is should be normal phenomenom. My other high impedance meter (100meg) throws needle to FSD in similar test so I weren't overly conserned with this.
« Last Edit: June 27, 2017, 09:15:40 pm by Vtile »
 

Offline Smokey

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Re: Keithley 197A owners' corner
« Reply #1 on: June 27, 2017, 08:06:57 pm »
I've got two 197A on the bench (along with two Keithley 175, two Keithley 199, and one Keithley 196).  I like 'em brown!
 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #2 on: June 27, 2017, 08:52:43 pm »
I have two Keithley 197s that are still in need of repair. I also have manually edited, corrected, and cleaned-up (remove artifacts from drafting and scanning) the schematics.

I have been building the equipment I need to test and repair them recently, so I should be fixing them soon.
 

Offline Vtile

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Re: Keithley 197A owners' corner
« Reply #3 on: June 27, 2017, 09:21:44 pm »
Reserved for the future.
 

Offline Vtile

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Re: Keithley 197A owners' corner
« Reply #4 on: June 27, 2017, 09:23:52 pm »
I have two Keithley 197s that are still in need of repair. I also have manually edited, corrected, and cleaned-up (remove artifacts from drafting and scanning) the schematics.

I have been building the equipment I need to test and repair them recently, so I should be fixing them soon.
Oh, nice.

Are the 197 and 197A internals (except the display) the same or is there a lot difference between the models?

@Smokey, how your two 197A meters react in the two lowest DC voltage ranges without probes?
« Last Edit: June 27, 2017, 09:26:33 pm by Vtile »
 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #5 on: June 27, 2017, 09:36:22 pm »
I have two Keithley 197s that are still in need of repair. I also have manually edited, corrected, and cleaned-up (remove artifacts from drafting and scanning) the schematics.

I have been building the equipment I need to test and repair them recently, so I should be fixing them soon.
Oh, nice.

Are the 197 and 197A internals (except the display) the same or is there a lot difference between the models?

@Smokey, how your two 197A meters react in the two lowest DC voltage ranges without probes?

They are essentially identical. The only differences involved are the plastics and the support for the backlight.
 
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Offline tooki

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Re: Keithley 197A owners' corner
« Reply #6 on: June 27, 2017, 09:47:51 pm »
I have two Keithley 197s that are still in need of repair. I also have manually edited, corrected, and cleaned-up (remove artifacts from drafting and scanning) the schematics.

I have been building the equipment I need to test and repair them recently, so I should be fixing them soon.
Oh, nice.

Are the 197 and 197A internals (except the display) the same or is there a lot difference between the models?

@Smokey, how your two 197A meters react in the two lowest DC voltage ranges without probes?
I've got one of each.

The 197A is fundamentally identical, other than adding an extra power rail on the display connector for the backlight, and the PCB layout is also different near the power transformer, because the 197A uses an IEC power cord, whereas the 197 has a fixed cord.

On the low ranges without probes, the numbers should be jumping all over the place.
 

Offline Vtile

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Re: Keithley 197A owners' corner
« Reply #7 on: June 27, 2017, 10:03:33 pm »
On the low ranges without probes, the numbers should be jumping all over the place.
Hmm... My unit is going up starting from 0 mV adding about 1 mV/s. Shorting the sense ports will zero it (and keep it on zero) as do shorting the input jacks.
 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #8 on: June 27, 2017, 10:16:46 pm »
On the low ranges without probes, the numbers should be jumping all over the place.
Hmm... My unit is going up starting from 0 mV adding about 1 mV/s. Shorting the sense ports will zero it (and keep it on zero) as do shorting the input jacks.

Perfectly normal.
 

Offline tooki

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Re: Keithley 197A owners' corner
« Reply #9 on: June 28, 2017, 07:32:32 am »
On the low ranges without probes, the numbers should be jumping all over the place.
Hmm... My unit is going up starting from 0 mV adding about 1 mV/s. Shorting the sense ports will zero it (and keep it on zero) as do shorting the input jacks.
Yes, that's what meters with high input impedance do. If it didn't it would be indicative of a fault.
 

Offline Vtile

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Re: Keithley 197A owners' corner
« Reply #10 on: June 29, 2017, 08:00:53 pm »
Good to hear. What a lovely meter, how I have managed without, especially the 4-wire resistance and the PN-junction test (only 1.5% typical accuracy unfortunately) are handy. Hmm... I finally have tool to make a voltage and current reference, need to do one now.  |O

Does anyone got further with the IEEE-488 module reverse engineering or the internal serial bus decoding? There were some discussion on this two or so years ago.
« Last Edit: June 29, 2017, 08:02:44 pm by Vtile »
 

Offline psient

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Re: Keithley 197A owners' corner
« Reply #11 on: October 08, 2017, 02:50:13 pm »
Hello: I am learning. I have a Mastech handheld (Ms8228). I was hoping to get something better for the bench. I haven't much money. I was looking at the Flukes until I read their service is not very helpful. If I found a inexpensively priced 197a I thought I'd buy it. I'm retired and pensioned at the low end having only been a community college adjunct with a PhD from a highly regarded university. I'd have a little bit more to spend but I lost mysocSec because of my windfall in earning that pension from teaching lower income students :-//

Is this  good decision in my seeking greater precision for the bench at a limited budget? I know this is the place owners comment but I figure this thread wouldn't be here if the DiMM wasn't worth about 75 bucks?

Thank you

Jon
 

Offline tooki

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Re: Keithley 197A owners' corner
« Reply #12 on: October 09, 2017, 08:36:14 am »
It’s a great meter. The only thing that newer/more expensive bench meters have is a) much faster readings (the 197A is about as fast as a good handheld meter, around 5 readings per sec), and b) VFD displays that are a bit easier to read than LCDs. For $75 it’s definitely worth picking up. 

One thing I love about the 197/197A is automatic 2 and 4 wire resistance. My K2015 requires you to choose manually.
 

Offline Vtile

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Re: Keithley 197A owners' corner
« Reply #13 on: October 09, 2017, 10:27:04 pm »
197 also supports the battery operation so it can serve also as field instrument or true floating meter.

The real qurstion is though. What is sufficient resolution for your use.

So far I  have been pleased with the functionality.
« Last Edit: October 09, 2017, 10:37:12 pm by Vtile »
 

Offline Cerebus

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Re: Keithley 197A owners' corner
« Reply #14 on: October 09, 2017, 11:40:21 pm »
Hadn't spotted this thread before. I picked up a 197 (non-A model) a few months back. It's become my daily driver bench meter. As LCDs go it's one of the easiest to read that I've encountered.

Mine needs a new switch for the AC/DC selection and it's a little troublesome tracking down one that's 'just right'. That style of switch used to be uniquitous but they're quite hard to find now. If anyone has any idea where to source one (short of cannibalising a dead meter) I'd be pleased to hear where.
Anybody got a syringe I can use to squeeze the magic smoke back into this?
 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #15 on: October 10, 2017, 12:49:25 am »
There is also a 197 Military version.  Which is an uplift on the standard 197 model.

Added design/features:
- Additional shielding over the processor
- Different (shielded?) cable going to the display/panel.
- Torroids on the power input and on the meter inputs.  Probably to reduce noise.
- Detachable AC power cord.  This makes more sense for battery operation.
- Typically has battery/charger.
- It also has a 10A fuse on the high amp input.  The standard 197/197A aren’t fused for the 10A input!!!
- Like the 197A it has 4 references in dB mode including 600 and 50 ohm.  The 197 only has 600 ohm.

rastro

Edit: Just remembered the model: AN/USM-486A; http://www.liberatedmanuals.com/TM-11-6625-3055-24P.pdf (Correction http://radionerds.com/images/7/72/TM_11-6625-3277-14.PDF)
« Last Edit: October 10, 2017, 03:19:40 pm by rastro »
 
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Offline tooki

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Re: Keithley 197A owners' corner
« Reply #16 on: October 10, 2017, 09:44:33 am »
There is also a 197 Military version.  Which is an uplift on the standard 197 model.

Added design/features:
- Additional shielding over the processor
- Different (shielded?) cable going to the display/panel.
- Torroids on the power input and on the meter inputs.  Probably to reduce noise.
- Detachable AC power cord.  This makes more sense for battery operation.
- Typically has battery/charger.
- It also has a 10A fuse on the high amp input.  The standard 197/197A aren’t fused for the 10A input!!!
- Like the 197A it has 4 references in dB mode including 600 and 50 ohm.  The 197 only has 600 ohm.

rastro

Edit: Just remembered the model: AN/USM-486A; http://www.liberatedmanuals.com/TM-11-6625-3055-24P.pdf
So basically, the military 197 is halfway between a 197 and 197A, plus the added fuse and CPU shield, toroid on the inputs, and with silkscreen on the analog section shielding, it looks like. (The standard 197A has a toroid on the AC jack, and the removable cord.)


Did you look at that manual? No way is it the right one; nothing about its construction matches a 197/197A, nor does it match the pictures you posted. It looks like it’s probably a Fluke design. (Looks like the Keithley 197-M is AN/USM-486A; that manual is for AN/USM-486U
« Last Edit: October 10, 2017, 09:53:38 am by tooki »
 

Offline tooki

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Re: Keithley 197A owners' corner
« Reply #17 on: October 10, 2017, 09:56:05 am »
Wow, there’s a beauty of a military 197 on eBay right now: supposedly unused (and it looks it!), fairly recent calibration

http://www.ebay.com/itm/KEITHLEY-197-M-2-BENCHTOP-MULTIMETER-NOS-SURPLUS-TESTED-GOOD-COMPLETE-SET-/182518230394?_ul=CH
 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #18 on: October 10, 2017, 10:04:07 am »
There is also a 197 Military version.  Which is an uplift on the standard 197 model.

Added design/features:
- Additional shielding over the processor
- Different (shielded?) cable going to the display/panel.
- Torroids on the power input and on the meter inputs.  Probably to reduce noise.
- Detachable AC power cord.  This makes more sense for battery operation.
- Typically has battery/charger.
- It also has a 10A fuse on the high amp input.  The standard 197/197A aren’t fused for the 10A input!!!
- Like the 197A it has 4 references in dB mode including 600 and 50 ohm.  The 197 only has 600 ohm.

rastro

Edit: Just remembered the model: AN/USM-486A; http://www.liberatedmanuals.com/TM-11-6625-3055-24P.pdf
So basically, the military 197 is halfway between a 197 and 197A, plus the added fuse and CPU shield, toroid on the inputs, and with silkscreen on the analog section shielding, it looks like. (The standard 197A has a toroid on the AC jack, and the removable cord.)


Did you look at that manual? No way is it the right one; nothing about its construction matches a 197/197A, nor does it match the pictures you posted. It looks like it’s probably a Fluke design. (Looks like the Keithley 197-M is AN/USM-486A; that manual is for AN/USM-486U

Agreed, that's just not a 197. Looks like a Fluke to me, too.

Also, it looks like the transformer has a shield around it too (neither of my 197s have that - I think the 197A does).

I am still having a ton of trouble repairing my 197s. Some of the circuits seem very complicated to me. Right now one of my units is reporting OL in every range, on every function. The other intermittently reports OL in between incorrect measurements. This 2nd one (OL then measure then measure then OL) seems to to have problems with the -9V rail intermittently. It's like the negative supply isn't sufficiently loaded or something. I really don't understand how the negative supply is created/regulated.

For noobs like myself, though, it turns out that two other models rely on essentially exactly the same signal path (modulo the details of the range switching): the Keithley 175, the 192, and the 197 all have basically the same process after signal conditioning, all the way to the microprocessor.

Now if only I could get an idea of what exactly is going wrong with my units. I might have to ask someone to take oscilloscope screenshots of certain measurements. I have so many measurements I doubt are correct, though, I almost don't know where to begin.

I actually have a battery board from the 2nd unit, but I never tried it until yesterday and it turns out it arrived dead. The CMOS inverter which provides the negative rail doesn't produce any negative voltage. Eventually, I'll have to order one of those ICs.

Unfortunately I don't yet have any low noise power power supplies (especially no split-rail or bipolar ones), so I can't bypass the AC power supply yet.
 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #19 on: October 10, 2017, 10:07:32 am »
Here's the real military manual:

AN/USM-486A.

edit:

This is not just a 197 with shielding.  There are no schematics or part numbers in the manual, but there is a layout diagram. Page 129. At first glance (through eyes who have spent a lot of time staring at these schematics), the entire digital section is totally different. The entire analog front-end looks exactly identical though. Other than the aforementioned 10A fuse, I don't see a single part out of place.

This board also has (gasp!) power rail test points!


edit 2: It looks like this manual has some nice reference material (namely waveform examples captured with an oscilloscope) that might prove very handy indeed!


edit 3: I did discover kind of a neat trick when trying to isolate noise and power rail problems that are influenced by transients and noise generated by the normal multimeter operation: You can select the Ohms reading and also (intentionally) select the AC button ON. This will cause all of the FET switching to stop, which will calm a lot of sources of noise down to their minimums.
« Last Edit: October 10, 2017, 10:26:31 am by technogeeky »
 
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Offline rastro

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Re: Keithley 197A owners' corner
« Reply #20 on: October 10, 2017, 03:23:31 pm »
Ooops. ;D

I grabbed the wrong URL in my browser.  I had a couple of tabs open trying to find different versions of the manual - hoping to find better quality schematics for Nibblers documentation work.  I've pasted a correction in my initial post.

Thanks
rastro
 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #21 on: October 10, 2017, 07:52:19 pm »
Not that it's strictly necessary, but here is a calibration instruction sheet for the 197 multimeter:

 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #22 on: October 11, 2017, 03:55:35 pm »
There are a number of JFETs that have Keithley only part numbers.  These are used for switching.  I ran across this thread which has some information on their characteristics.  Has anyone else looked into identifying substitutes?

https://groups.io/g/TekScopes/topic/jfet_needed_for_range/966846?p=Created,,,20,1,20,0
 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #23 on: October 11, 2017, 04:07:48 pm »
I did a further tear down of a 197M.  As pointed out, there are some significant differences compared to the 197/197A.  I'll attach a few pictures.

I'm going to leave the instrument apart for this next week.  So if some one has any questions or picture requests I can follow up.

-rastro
 
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Offline rastro

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Re: Keithley 197A owners' corner
« Reply #24 on: October 11, 2017, 04:09:27 pm »
197M tear down...additional pictures.
 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #25 on: October 11, 2017, 06:21:37 pm »
wow look at all that via stitching or ground plane action going on. very nice.
 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #26 on: October 11, 2017, 08:22:31 pm »
Additional 197M Observations:
1. The display board has 197A written on it.  However it does not have the additional components for the back light. 
2. I doubt it would support the GPIB option due to physical constraints of the added shield.  However it still has the connector for the option.
3. TheMC68HC711E9CFN2 probably has the system firmware loaded into it.  These chips are available but I don't know if the firmware is readable.

rastro
 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #27 on: October 12, 2017, 03:12:46 am »
Some differences from looking at pictures posted:

Y101 was 3.276800 MHz, is 2.62144 MHz (HEF4040 is still used to divide this down, and the ratio between the two crystals is 1.25. so... what does that mean w.r.t. the timing of the charge pump and integration cycle)

U109 was TI741, is AD711 ("enhanced replacement for LF411 and TL081")

U101 was TLC272lcp, is TLC27L2cp (not the same part at all: the 27L2 uses about 200 times less power (~ worst-case 100 µA versus ~ avg. 2000 µA typical))[1]



[1]: I'm confused by this substitution. This is a pretty important part in this multimeter, but these chips are very different. Both of these devices were first available in the same year. A lot of figures in the datasheet are incomparable because they have different reference points (TLC27L2 is specified into a 1M, TLC272 is specified into 10k?). CMRR is ~ 97 dB for the TLC27L2 chip, and ~ 88 dB for the TLC272.

TLC27L2 (new) versus TLC272 (old):
  • ~ 100 µA vs 2000 µA - supply power (worst case vs typical case) -  :-+
  • 97 dB vs 88 dB - CMRR -  8)
  • ~ 100 kHz vs ~ 2 MHz -  ???




Speculation about things I can't see:

It looks like all three zeners VR101, VR102, and VR103 are different from the unit I have. I'm curious if you can identify the part numbers on these.

I'm curious to know if you can identify which lines have inductors/ferrites on them (one long one above the CPU, two blocky ones near 74HC79 and CD4075) - and perhaps the inductors/ferrites themselves (probably too much trouble for the ferrite).

 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #28 on: October 12, 2017, 03:40:30 am »
There are a number of JFETs that have Keithley only part numbers.  These are used for switching.  I ran across this thread which has some information on their characteristics.  Has anyone else looked into identifying substitutes?

https://groups.io/g/TekScopes/topic/jfet_needed_for_range/966846?p=Created,,,20,1,20,0

First, one handy thing that I've learned is that basically all of the ways people have produced JFETS (at least until this multimeter was made, and perhaps afterwards) are enumerated by their construction process. This PDF lists them all, and gives you an idea of why one process might be used as opposed to another. It also shows sample device numbers, and die construction.

Yep, I have seen it and I bought a few of a bunch of different nearby JFETs to test. I wanted to draw their characteristic curves and compare them for this purpose (or at least be able to understand how the existing ones were matched or paired (which in this case might not be the same thing)). However, the curve tracer I built only tests BJTs and only NPNs at that. I need to modify the circuit to test PNPs (which might be easy, maybe trivial) and then modify it to do JFETS (at the very least meaning going negative with voltage).

The two things to figure out is why they were chosen in the first place, and then why they were matched.

I think the current guesses for each are:

Why were Q104-Q113 chosen?

  • ultra-low leakage (process 50, process 51 ~ J113)
  • low on resistance (process 50, process 58 ~ J110)

I don't have any info to guess what's right or wrong here, yet.

Why are those particular ones paired (e.g. Q104 and Q105)?

  • They're not, but Q104-Q109 (and maybe the rest) are matched overall to fall on two pinch-off voltages, so they can control 6 devices with only 2 voltage levels.
  • They are matched in pairs, for _____?

At the end of the day, if someone has one of these parts which is dead for sure, perhaps they can dissolve and microscope it (or send it to me, or someone who can) so we can just look at the die and figure out which process they are.

I have already received the following parts for attempting to see if they could be matches (along with their process, if I know it):

  • J107 (p. 59)
  • J109 (p. 58)
  • J111 (p. 51) (from 3 different mfgs, one is a PF5102)
  • J112 (p. 51)
  • J113 (p. 51)
  • J175 (p. 88) (not sure why I got this?)
 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #29 on: October 12, 2017, 08:34:47 am »
Well that's a little fortuitous. After reading my above comments about TLC272CP vs TLC27L2CP, I went and found the original part I removed from my 2nd unit (which was intermittent OL and a bad reading).

This unit has some other marking (SN something something). In any case, this unit now (mostly) works. It makes sense, too: putting a TLC272CP in there draws way too much current, which is far more than the 6.4V zener (which is the precision reference) can handle. Putting this lower power opamp in makes it work.

Now there are two remaining problems:

* everything is a little bit off in the first two or three ranges of each function
* in some of the upper ranges, things are way off

The worst problem:
* in ohms mode, after some unspecified amount of time, the multimeter puts more and more voltage (and current) out. When it's reading roughly correct (only roughly), it's putting about 0.019 volts and some small amount of current. However, after some time (or even right after turn-on sometimes), it's putting 4.030 volts and 0.1008 mA into the red and black terminals. At the same time, it oscillates between measuring ~ 173.xxx ohms and OL.

So I bet the current is correct, but the voltage is not. I'm not sure, though. I'm too tired to keep working on it.

Any hints on where to begin?

edit: perhaps I spoke too soon. Now my -V rail is at +1V. :/
« Last Edit: October 12, 2017, 12:55:33 pm by technogeeky »
 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #30 on: October 12, 2017, 01:58:26 pm »
...
It looks like all three zeners VR101, VR102, and VR103 are different from the unit I have. I'm curious if you can identify the part numbers on these.

I'm curious to know if you can identify which lines have inductors/ferrites on them (one long one above the CPU, two blocky ones near 74HC79 and CD4075) - and perhaps the inductors/ferrites themselves (probably too much trouble for the ferrite).
I'll take a look.  I might take a few days since I'm in the middle of replacing my work bench.
-rastro
 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #31 on: October 12, 2017, 02:10:34 pm »
... I went and found the original part I removed from my 2nd unit (which was intermittent OL and a bad reading)....
... In any case, this unit now (mostly) works. It makes sense, too: putting a TLC272CP in there draws way too much current, which is far more than the 6.4V zener (which is the precision reference) can handle. Putting this lower power opamp in makes it work.

Glad to hear you making some progress.  It sounds like you tried upgrading to a part with better specifications but it introduced other problems.  Reverting clears those issues.

One thing I'm a little confused on is that in reply # 27 you indicate that TLC27L2 (new) uses less power than the  TLC272 (old) original part.  Maybe I'm not reading something right.  :-//

-rasto
 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #32 on: October 12, 2017, 03:18:17 pm »
... I went and found the original part I removed from my 2nd unit (which was intermittent OL and a bad reading)....
... In any case, this unit now (mostly) works. It makes sense, too: putting a TLC272CP in there draws way too much current, which is far more than the 6.4V zener (which is the precision reference) can handle. Putting this lower power opamp in makes it work.

Glad to hear you making some progress.  It sounds like you tried upgrading to a part with better specifications but it introduced other problems.  Reverting clears those issues.

One thing I'm a little confused on is that in reply # 27 you indicate that TLC27L2 (new) uses less power than the  TLC272 (old) original part.  Maybe I'm not reading something right.  :-//

-rasto

Yeah, basically: at some point in the last, I decided (through pictures or through reading on the forum) that U101 is TLC272CP. But it's possible it has always been TLC27L2CP, and I just identified it wrong and had ordered the wrong part, etc.

I did not consciously pick TLC272CP as an upgrade, I thought it was the intended part. But I'm not 100% sure that is the problem yet.

I really don't understand why they don't just use standard voltage regulators everywhere in this unit. Even the Keithley 175 uses 7805 and 7915 regulators. Perhaps they consume too much power for the battery option.  :-//

 

Offline timb

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Keithley 197A owners' corner
« Reply #33 on: October 12, 2017, 04:58:26 pm »
197M tear down...additional pictures.

For what it’s worth, that battery board appears to be identical to the 197A’s battery option PCB. It’s essentially a discrete shunt regulator (using a TO220 transistor and thermistor) to trickle charge the NiCD pack, along with a charge pump inverter to generate the negative rail, plus a comparator to monitor the battery voltage, the output of which goes to the low battery symbol on the LCD.

Awhile back I sat down and tried to come up with a modern replacement using a single cell LiOn battery, charger IC and boost converter (the NiCD pack is 12V), however it’s surprisingly difficult!

Why? Well, the power switch on these meters is placed on the low voltage side of the main power transformer (after the bridge rectifier even). The battery connects between the rectifier and power switch. Since the transformer puts out between 13.5 and 16V and that voltage is higher than the battery pack’s nominal voltage (12V), the battery charges through that connection when the unit is plugged in.

When the unit is unplugged, the battery supplies 12V out through that same connection. The charging is completely dumb, relying on the way NiCD batteries charge. (Don’t try replacing the pack with NiMH cells, they’ll overcharge and eventually be ruined.)

So, you can see how it would be difficult to create a replacement that powers a lithium charger and feeds back power from a boost converter over the same connection. I couldn’t figure out a simple way of doing it, short of monitoring the voltage with a micro or comparator and using that to switch the charging circuit off and start the boost converter. (Actually, there is a connection to the “ON” side of the switch, so that could be used to start the inverting and boost converters somehow. That still doesn’t solve the problem of only running the charging circuit when plugged in.)

Anyway, it’s an interesting problem. One I a might take another crack at one day.

Oh yeah, there’s a post on the forums somewhere, where a member reverse engineered the display protocol used by 197 and 197A. If I recall, he used a micro to intercept the data and format it for another LCD. (The LCD in his unit had gone bad.)

I actually found an OLED display with nearly identical dimensions as the OEM LCD. That was another project I never quite got around to. (I ended up fixing my LCD by disassembling it and cleaning the zebra strips and PCB contacts with DeoxIT. I also applied a bit of tape around the LCD’s frame, so it would press harder against the front panel when screwed in, thus keeping more pressure on the zebra strips. Additionally  I found that applying a steel strip to the back of the top of the front panel, with epoxy, also helps to alleviate any flexing, which in turn keeps constant pressure on the LCD’s contacts.)
« Last Edit: October 12, 2017, 08:10:59 pm by timb »
Any sufficiently advanced technology is indistinguishable from magic; e.g., Cheez Whiz, Hot Dogs and RF.
 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #34 on: October 12, 2017, 07:48:32 pm »
...
Oh yeah, there’s a post on the forums somewhere, where a member reverse engineered the display protocol used by 197 and 197A. If I recall, he used a micro to intercept the data and format it for another LCD. (The LCD in his unit had gone bad.)

I started a thread on the LCD replacement a few years back - but couldn't find a clean way to mod it into the DMM.  I think the nibbler also did some work on this.
https://www.eevblog.com/forum/projects/keithley-197-led-display-hack/msg493365/#msg493365

I also recall someone else staring another thread on this - I think he was from Europe.  He did a much better job of of analyzing the signals.  I just can't find his thread on the eevblog.  Maybe someone knows?

timb;
Please post the P/N & Mfg. of the display.  Who knows someone may want to carry this forward.

-rastro
 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #35 on: October 12, 2017, 07:59:09 pm »
...
Oh yeah, there’s a post on the forums somewhere, where a member reverse engineered the display protocol used by 197 and 197A. If I recall, he used a micro to intercept the data and format it for another LCD. (The LCD in his unit had gone bad.)

I started a thread on the LCD replacement a few years back - but couldn't find a clean way to mod it into the DMM.  I think the nibbler also did some work on this.
https://www.eevblog.com/forum/projects/keithley-197-led-display-hack/msg493365/#msg493365

I also recall someone else staring another thread on this - I think he was from Europe.  He did a much better job of of analyzing the signals.  I just can't find his thread on the eevblog.  Maybe someone knows?

timb;
Please post the P/N & Mfg. of the display.  Who knows someone may want to carry this forward.

-rastro

Yeah, it was me. I have a fully working Arduino code which deciphers 100% of the data sent to the display controller (including display screens, including calibration, etc). It displays the data currently to a standard 16x2 display. I thought I had shared it already, but perhaps I did not.

Another advantage of the 16x2 display situation is that, with the aid of only two small square plastic sleeves (to cover the area outside of the 16x2 display but still visible through the original aperture), the original PCB can be re-used. This process puts a tiny amount of strain on the PCB, but it can easily take it. This way you can retain the original buttons easily and don't even need to manufacture a new PCB.

I promise I'll post my code soon (by the end of the weekend) because the decode table (which converts SPI bytes to ASCII bytes) will be useful regardless of all the other code.

This project is what killed my first unit: my arduino board was not optoisolated from the power supply of the K197, and when I measured an AC mains signal (I think polarity-reversed), the resulting explosion fried the regulator on my arduino mega, the LCD, and a few of the logic chips on the K197. (the arduino board was connected to my PC at the time, which brought a real ground reference back into the picture).

For what it's worth, I am also pretty certain that all of the same information (and perhaps a little bit more information) can be gotten from the 2 or 3 pins which go from the K197 to the GPIB board. I was in the process of trying to prove this/capture some correlated bits when I blew up my meter.

I will certainly do so soon. I am determined to get my two units working properly. Even if they are out of calibration, I can figure that out later.
« Last Edit: October 12, 2017, 08:05:56 pm by technogeeky »
 

Offline tooki

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Re: Keithley 197A owners' corner
« Reply #36 on: October 16, 2017, 12:55:40 pm »
I’d love to make a custom replacement display board. Just too elegant!

technogeeky, I sent you a PM, we should hop on Skype again and work on our 197/197A issues some more.
 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #37 on: October 16, 2017, 05:00:06 pm »
Finally found the other contributor "Maxior" who was also decoding the LCD display communications.  Very nice summary.  This was a couple of years back as well.
https://www.eevblog.com/forum/projects/modding-a-keithley-197how-to-print-on-front-panels/msg790844/#msg790844

Also here's some work on installing a back light @ reply#11:
https://www.eevblog.com/forum/testgear/modding-a-keithley-197/msg725392/#msg725392

-rastro
 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #38 on: October 19, 2017, 03:56:20 pm »
...
It looks like all three zeners VR101, VR102, and VR103 are different from the unit I have. I'm curious if you can identify the part numbers on these.

I'm curious to know if you can identify which lines have inductors/ferrites on them (one long one above the CPU, two blocky ones near 74HC79 and CD4075) - and perhaps the inductors/ferrites themselves (probably too much trouble for the ferrite).
I'll take a look.  I might take a few days since I'm in the middle of replacing my work bench.
-rastro

Back with some information on 197M parts:

1. L101 & L102 - I don't have much information.  You can see some of the connections on the back picture of the board.  The front side is difficult to trace out because of vias and passing under components.  On the top of these inductors are 3 wire loops that measure less than 1-ohm between them.
2. E101 - Inductor near CPU.  Connected to  U120/PIN-04 and U124/See Pic                           
3. VR's : I did not want to unsolder components.  Could identify marking on 2 components.
    - 101: Gray; marked IN75/6A304(Possible 1N756A)
    - VR 102: Glass; marked 357                       
    - VR103 : conveniently soldered face down
-rastro
 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #39 on: October 25, 2017, 08:56:16 pm »
Looking for some suggestions or ideas on resurfacing the 4 soft mode keys next to the LCD display.  These are rubber with the buttons with some kind of conductor (carbon??) impregnated.  I have a set that is very difficult to make good contacts.  It seems like the conductive treatment is worn-off or gone so resistive it can't activate the mode button. 

I've done all the cleaning to the PCB and rubber button to no avail.  I want to keep these buttons original.  Has anyone tried to resurface this type of button?

-rastro
 

Offline tooki

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Re: Keithley 197A owners' corner
« Reply #40 on: October 26, 2017, 05:04:32 am »
Looking for some suggestions or ideas on resurfacing the 4 soft mode keys next to the LCD display.  These are rubber with the buttons with some kind of conductor (carbon??) impregnated.  I have a set that is very difficult to make good contacts.  It seems like the conductive treatment is worn-off or gone so resistive it can't activate the mode button. 

I've done all the cleaning to the PCB and rubber button to no avail.  I want to keep these buttons original.  Has anyone tried to resurface this type of button?

-rastro
Though those conductive pads are apparently available online, I think it’s extremely unlikely that they’ve failed. What kind of resistance do you get if you probe a conductive pad with a DMM? Depending on where and how hard I probe, I get between about 1-25Kohms. If I measure the resistance of a pressed button on the connector, it’s up to about 40K for a light press, under 1K for pressing down really hard. (Follow the PCB traces, you’ll see that the buttons have one common, plus one line for each button, leading straight to the ribbon cable.) Test the resistance at a few different points to see if the signal is getting lost somewhere.
 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #41 on: October 26, 2017, 01:17:26 pm »
tooki,

Thanks for the recommendations.  I replaced the 4 keys using one from a K175 parts unit.  It fixed the problem. So it's not a connection/signal issue elsewhere. 
I didn't realize they sold sheets and buttons of 'conductive pads' but apparently they do.  Thanks for the suggestion and search description.

I agree these usually don't go bad.  I've always been able to clean them to remedy poor contact issues.  I'll have to look at the resistance on the failed pads.  Visually it looked like they had the imprint of the PCB contact side imprinted in it - suggesting mechanical wear or hardening of the rubber.

-rasto
 

Offline tooki

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Re: Keithley 197A owners' corner
« Reply #42 on: October 26, 2017, 05:39:35 pm »
Well, substitution is absolute proof of the culprit! Weird, in my 197, they're still soft and work fine, and your 197M should be younger, if anything. I wonder if maybe storage conditions affect the rubber aging.

In any case, you should be able to get the little pads and fix it! :)
 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #43 on: October 28, 2017, 12:49:12 am »
Some good and OK news on my repair processes:

My old unit (killed by measuring AC and some ground connection via USB to earth mains -- from my LCD replacement solution) I finally got some life back into it. The ADC and integrator basically had no activity. It turned out to be one of the traces on the board for U105.

I had already replaced U105 (it was one of the chips which died), and I added a socket. But either the trace was vaporized by the original problem, or bad soldering work. In any case, no matter how many times I tried to reflow the joint to include the trace (the cut in the trace was only a millimeter or two away from the U105 pin that it connected to), it wouldn't connect. So I gave up and just used a short bodge wire.

After that, now the ADC is running again!

That older meter is not out of the woods yet, though. The only range that is even close to accurate is the two lowest voltage ranges. All resistance ranges and all but the lowest current ranges show basically nonsense values.

I'm also suspicious of the stability of the voltage measurements. I used my Keithley power supply (2304), which isn't the cleanest supply (although the noise is very ... random? gaussian?). And basically no matter what setting I pick for the Keithley, the meter instantly locks on to some (reasonable, if a little bit off) voltage value -- all 5.5 digits, no drift at all.

This makes me very suspicious, but it is certainly progress compared to before.


As for the newer of my two meters, I have been testing by completely disconnecting the negative voltage rail entirely (by removing the resistor and capacitor), and powering it using the aforementioned Kiethley power supply. One of the cool features of the power supply is that it reads back (and sinks) the voltage and current present on the connected nodes, no matter if the supply is ON or OFF. Furthermore, you can "force" the node into compliance.

This came in handy when I noticed that, when the power supply was OFF, the negative rail came in at -0.640V with some small (sub 1mA) current. In other words, the negative rail was going positive somehow. I suspected this was because of some short to a positive rail, but I was unable to find it. In any case, I tried correcting it by forcing the rail to zero (by setting the compliance voltage to 0.001 volts). Because the current measurement on the supply is so good (it has a 5mA range), I could easily see leakage currents change as certain multiplexing JFETs were turned on or off! We're talking values like 0.0145 mA to 0.0165 mA!

In any case, when I powered the negative rail with 9V, things lit up. Again, pretty much all of the measured values are pretty far off; but at least it's alive. And there isn't the kind of stability the old meter has. I also am pretty sure that two of the multiplexing JFETs are bad: Q110 and Q112 both exhibit a pretty huge drift (like, 100s of mV) in the gate voltage after being turned on (that is, when the voltage is near or above 0V). I can't imagine that's correct, and it's slow enough (and bidirectional) that it seems thermal.

I'm sorry for the rambling, I'm just putting a log of what's going on in case it randomly helps someone else. I think I would have made more progress quickly if I had just went ahead and removed the multiplexing JFETs, but I really don't want to unnecessarily contaminate the sensitive/guarded sections of the meter, because if I screw up calibration I really have no way to get back to calibration.


For what it's worth,  the military manual that was posted above is a great resource. None of the Keithley 197 manuals so far (there are three or four editions out there) have an actual picture of any waveforms (be they oscilloscope traces or just theoretical diagrams). I knew what the waveform of the 197's integrator/ADC step should look like because of the Keithley 175, but you never know.

In any case, despite the fact that the military version manual uses a different CPU (and a different crystal frequency), all of the troubleshooting values in the military manual are identical to the steps listed in the normal Keithley 197 manuals, except oscilloscope
 traces are pictured. I don't know what the "alternate" trace is, but I don't see it on either of my two units.




 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #44 on: October 31, 2017, 09:40:34 am »
I finally have success on my older meter. The final thing that needed repair was the PIA chip. Pin 8 was dead - I discovered this because it was effectively floating, which I could notice when I probed things with a 1x scope probe. The output (pin 8) which goes to U103 pin 11, which turns Q112 on/off.

As is the downside with JFETs, if you aren't actively turning them off, then they are on. So Q112 wasn't getting turned off.

So as of now, all voltage (both AC and DC) and current (AC and DC) ranges work!

Resistance measurement is still problematic, and I'm not sure why yet. I thought it might be Q110 but since that's used in the higher DC voltage ranges, I guess it's fine.

Anyway, good progress!
 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #45 on: October 31, 2017, 06:03:33 pm »
Great News.  Nice Tshooting;
 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #46 on: November 01, 2017, 05:33:51 pm »
So I worked on the resistance stuff last night. Normally, I get completely nonsense readings. For a long time last night, I was getting sensible readings on all ranges except the lowest range. But there are two bizzare things:

1) The way I was able to get sensible readings was by connecting an oscilloscope probe to the forward side of R111 (though the backward side of R111 worked as well) -- along with connecting it to ground. Both x1 and x10 settings worked. If i disconnected this oscilloscope probe, then the readings once again cycled around and were nonsensical - often times just OL, but sometimes actual values. But again, when the probe was connected here, I would get readings that are within 1-2% of the correct value on several ranges (and again, except the 200 Ohm range which reads OL).

2) However, after some time later, and after I added a ferrite to the power input of the meter overall (to try and filter some of the noise that my UPS is putting back on the power/ground lines), this trick no longer worked. I am currently unable to get any sensible resistance readings.

I really don't understand what is going on here. I can't imagine that stray capacitance or inductance is making a huge difference. I can only imagine that somehow the 1M or 10M connection to ground is what made a difference, and this somehow reset or overcame some connection that is otherwise floating (like a JFET which is totally open but should itself have a 1M or so resistance).

But if it's Q112 that is broken (or for that matter, any of Q110-Q113) then why are the voltage and current ranges working (granted: they are actually somewhat off, but only a few percent).

Any advice at all would be very welcome.
 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #47 on: November 03, 2017, 05:49:20 am »
 :scared:

My original Keithley 197 is fixed! And even better news, it's essentially exactly back in the calibration state it was before!

The last remaining problem was basically that the LO input was floating. This meant that any measurements I was taking (voltage, current, or resistance) were being taken through the 220k resistor to the LO SENSE input. This explained the slightly wrong readings for voltage, and why resistance measurement didn't work. As for why the above happened (why a 1M/10M resistor to ground from the scope probe caused resistance measurements to run, even if incorrect), I can't fully explain that (other than connecting something to ground, which was floating).

The trace from the LO input which snakes off under the range switches and ultimately to the Voltage switch on pin 4. This was completely blown, lifted off the board. I didn't see it because it's hidden underneath a current shunt and the range switches. I cut this trace off from both ends (to avoid coupling any noise into it), and ran a bodge wire in its place.

Now all the measurement functions work fine. My 1M 0.5% resistor reads 0.99998 MOhm. My voltage calibrator readings are basically the same as before the explosion. Bottom line, everything's back to working!

Now I have to find out what's wrong with my 2nd unit, re-create the Arduino (or probably ESP32-wireless so I can use these meters for datalogging without connecting anything to a PC directly. USB isolators are expensive.

I still need to find a replacement for the protection transistors GES5818. Or I need to find out why they picked those specific transistors. I'm guessing it's for the low (< 5pF max) capacitance. One of them was dead, and I broke the leads off of another one.

I'm so happy!

Thanks also to joe_z on ##electronics on FreeNode who helped a great deal.
 

Offline Cerebus

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Re: Keithley 197A owners' corner
« Reply #48 on: November 03, 2017, 01:52:10 pm »
I still need to find a replacement for the protection transistors GES5818. Or I need to find out why they picked those specific transistors. I'm guessing it's for the low (< 5pF max) capacitance. One of them was dead, and I broke the leads off of another one.

This thread: Using Transistors as Diodes, is on the go, and there have been mentions of some obsolete transistors that were much loved in these rôles. Might be worth dipping in and seeing if anyone recognises that part number.
Anybody got a syringe I can use to squeeze the magic smoke back into this?
 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #49 on: May 08, 2018, 04:49:13 am »
I wanted to chime in here in case anyone is watching. I had promised several times to release some code for doing 16x2 LCD replacement of the broken LCDs for these instruments.

As far as I know, the mapping from native LCD to a 16x2 LCD is complete and total. All displays for all modes translate to something on the 16x2 display. This includes status information, measurements, store/recall modes, dB mode, and troubleshooting modes. I even found a mode that I couldn't find in the manual: with GPIB card installed it sometimes says "OUT" using the alphanumerics.

I am in the process of extending the functionality shown below further, including:

* porting to Arduino Uno (trivial, just test which pins work)
* porting to ESP32 (wifi and/or bluetooth)
* release better documentation
* add back plotting support (native to Arduino)
* adding exporting for something to do plotting (like for sigrok)
* adding the ability for two of these devices to combine, displaying a combined stat on screen (power, for instance)

But since I just got back to a workable point, I figured I'd release the code so you guys can try to use it and/or comment or ask questions.

The Arduino project is located on GitHub. It is designed for a Arduino 2650.

Once I make a little more progress, I'll make an new thread about this with more documentation, pictures. I am essentially assuming you can do the 16x2 display wiring yourself (there are plenty of guides), and then you only need to pick off the GND, SCK, (MO)SI, and SS pins. If you want, you can skip the 16x2 display altogether and use serial as a display.
« Last Edit: May 08, 2018, 04:52:00 am by technogeeky »
 
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Offline Vtile

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Re: Keithley 197A owners' corner
« Reply #50 on: May 10, 2018, 07:47:39 pm »
@ technogeeky: I'll give 10 for that project ^^  :)
 
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Offline tooki

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Re: Keithley 197A owners' corner
« Reply #51 on: May 19, 2018, 08:14:01 pm »
I wanted to chime in here in case anyone is watching. I had promised several times to release some code for doing 16x2 LCD replacement of the broken LCDs for these instruments.

As far as I know, the mapping from native LCD to a 16x2 LCD is complete and total. All displays for all modes translate to something on the 16x2 display. This includes status information, measurements, store/recall modes, dB mode, and troubleshooting modes. I even found a mode that I couldn't find in the manual: with GPIB card installed it sometimes says "OUT" using the alphanumerics.

I am in the process of extending the functionality shown below further, including:

* porting to Arduino Uno (trivial, just test which pins work)
* porting to ESP32 (wifi and/or bluetooth)
* release better documentation
* add back plotting support (native to Arduino)
* adding exporting for something to do plotting (like for sigrok)
* adding the ability for two of these devices to combine, displaying a combined stat on screen (power, for instance)

But since I just got back to a workable point, I figured I'd release the code so you guys can try to use it and/or comment or ask questions.

The Arduino project is located on GitHub. It is designed for a Arduino 2650.

Once I make a little more progress, I'll make an new thread about this with more documentation, pictures. I am essentially assuming you can do the 16x2 display wiring yourself (there are plenty of guides), and then you only need to pick off the GND, SCK, (MO)SI, and SS pins. If you want, you can skip the 16x2 display altogether and use serial as a display.

So I finally got around to getting this up and running. Great work!

I ported it to Uno (since it makes no damned sense to use up a Mega2560 for this!).

Here's the pin defs I'm using:

Code: [Select]
/* LCD: Pin Definitions
 */
/*      name    pin   //  color   used?   req?  uniq?   notes */
 #define RS_13   7    //          yes     yes   no      any ADC pin will work
 #define RW_12   8    //          yes     no    no      any ADC pin will work
 #define E__11   9    //          yes     yes   no      any ADC pin will work

/*      name    pin   //  color   used?   req?  uniq?   notes */
 #define D4      3    //          yes     yes   no      any ADC pin will work
 #define D5      4
 #define D6      5
 #define D7      6

and

Code: [Select]
/* SPI: Pin Definitions

    Note: the o_ is supposed to be a cute convention meaning "pin".
      so o_SCK is to be read "pin_SCK"
*/
/*      name    pin   //  color   used?   req?  uniq?   notes */
 #define o_GND   GND   //  blue    yes     yes   no      this isn't a real pin in the UI, but it must be connected -- P1006 pin 4
 #define o_SS    10    //  red     yes     yes   no      (Mega2650) this is the only pin that can be SS or CS -- P1006 pin 14
 #define o_SCK   13    //  yellow  yes     yes   no      (Mega2650) this is the only pin that can be SPI clock -- P1006 pin 12
 #define o_MOSI  11    //  orange  yes     yes   no      (Mega2650) this is the only pin that can listen from a masterm -- P1006 pin 13
 #define o_MISO  12    //          no      no    no      (Mega2650) this is the pin you'd use to speak to slave as master
 #define o_CD    49    //          no      no    no      one might be tempted to use command/data as a interrupt trigger, but we wouldn't get state info
(I changed the colors to my wires :P)


I turned off the "twiddler", since it serves no real purpose, and with the default timings, appears just as a pale flickery mess on my LCD.

I also found a bug: k197-spi.cpp declares #include "k197-state.h", but that header isn't included in the repository. But it doesn't seem to actually be used, since I just commented out the include and then it compiled fine.

Regarding documentation: Yeah, needs to be made more obvious! I would make a clear note of the SPI line names used in the Keithley documentation, as opposed to the official SPI names you used in the forum post. Ultimately, I'd love to know how the code works, so I can consider using something other than a character LCD, perhaps an LED display driven by a MAX7219 or something.

We should Skype again sometime and kibitz about it. :)
« Last Edit: May 19, 2018, 08:16:45 pm by tooki »
 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #52 on: May 20, 2018, 01:10:58 pm »
I wanted to chime in here in case anyone is watching. I had promised several times to release some code for doing 16x2 LCD replacement of the broken LCDs for these instruments.

As far as I know, the mapping from native LCD to a 16x2 LCD is complete and total. All displays for all modes translate to something on the 16x2 display. This includes status information, measurements, store/recall modes, dB mode, and troubleshooting modes. I even found a mode that I couldn't find in the manual: with GPIB card installed it sometimes says "OUT" using the alphanumerics.

I am in the process of extending the functionality shown below further, including:

* porting to Arduino Uno (trivial, just test which pins work)
* porting to ESP32 (wifi and/or bluetooth)
* release better documentation
* add back plotting support (native to Arduino)
* adding exporting for something to do plotting (like for sigrok)
* adding the ability for two of these devices to combine, displaying a combined stat on screen (power, for instance)

But since I just got back to a workable point, I figured I'd release the code so you guys can try to use it and/or comment or ask questions.

The Arduino project is located on GitHub. It is designed for a Arduino 2650.

Once I make a little more progress, I'll make an new thread about this with more documentation, pictures. I am essentially assuming you can do the 16x2 display wiring yourself (there are plenty of guides), and then you only need to pick off the GND, SCK, (MO)SI, and SS pins. If you want, you can skip the 16x2 display altogether and use serial as a display.

So I finally got around to getting this up and running. Great work!

I ported it to Uno (since it makes no damned sense to use up a Mega2560 for this!).

Here's the pin defs I'm using:

Code: [Select]
/* LCD: Pin Definitions
 */
/*      name    pin   //  color   used?   req?  uniq?   notes */
 #define RS_13   7    //          yes     yes   no      any ADC pin will work
 #define RW_12   8    //          yes     no    no      any ADC pin will work
 #define E__11   9    //          yes     yes   no      any ADC pin will work

/*      name    pin   //  color   used?   req?  uniq?   notes */
 #define D4      3    //          yes     yes   no      any ADC pin will work
 #define D5      4
 #define D6      5
 #define D7      6

and

Code: [Select]
/* SPI: Pin Definitions

    Note: the o_ is supposed to be a cute convention meaning "pin".
      so o_SCK is to be read "pin_SCK"
*/
/*      name    pin   //  color   used?   req?  uniq?   notes */
 #define o_GND   GND   //  blue    yes     yes   no      this isn't a real pin in the UI, but it must be connected -- P1006 pin 4
 #define o_SS    10    //  red     yes     yes   no      (Mega2650) this is the only pin that can be SS or CS -- P1006 pin 14
 #define o_SCK   13    //  yellow  yes     yes   no      (Mega2650) this is the only pin that can be SPI clock -- P1006 pin 12
 #define o_MOSI  11    //  orange  yes     yes   no      (Mega2650) this is the only pin that can listen from a masterm -- P1006 pin 13
 #define o_MISO  12    //          no      no    no      (Mega2650) this is the pin you'd use to speak to slave as master
 #define o_CD    49    //          no      no    no      one might be tempted to use command/data as a interrupt trigger, but we wouldn't get state info
(I changed the colors to my wires :P)


I turned off the "twiddler", since it serves no real purpose, and with the default timings, appears just as a pale flickery mess on my LCD.

I also found a bug: k197-spi.cpp declares #include "k197-state.h", but that header isn't included in the repository. But it doesn't seem to actually be used, since I just commented out the include and then it compiled fine.

Regarding documentation: Yeah, needs to be made more obvious! I would make a clear note of the SPI line names used in the Keithley documentation, as opposed to the official SPI names you used in the forum post. Ultimately, I'd love to know how the code works, so I can consider using something other than a character LCD, perhaps an LED display driven by a MAX7219 or something.

We should Skype again sometime and kibitz about it. :)

tooki:

I'm glad to hear you have it working!

I *almost* have the same thing working on an ESP32. I have a persistent problem with the SPI bus and reading the last status byte (which contains mode information).

And I agree documentation needs to be better. I have a little more documentation (namely I made pictures of the wiring connections at each step), but it was wrong until I re-did it so I didn't include it to avoid confusing more people.

I'll be happy to skype about it.

-tg
 
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Online trobbins

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Re: Keithley 197A owners' corner
« Reply #53 on: June 06, 2018, 08:51:19 am »
I was lucky to pick up a faulty 197 with IEEE-488 interface with Analog Output and RF Probe options. 

One half winding of the power transformer primary was open-circuit.  240VAC is local, so I just use an external step-down transformer - works like a charm!
 
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Offline GregDunn

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Re: Keithley 197A owners' corner
« Reply #54 on: September 09, 2018, 01:07:05 am »
I found a 197A with IEEE-488 and analog out today at the Louisville hamfest.  $45 and in near-perfect shape (a few little scratches on the rear panel labels).  It tracks beautifully with my Fluke 8600 over the voltage range I'm interested in - and it's nice to see those extra digits, accurate or not.  Cheapest bench meter I've ever bought.  Oddly, it came without the handle and with little caps installed to cover the holes.  I don't think I've ever seen that before.

I do see why people are interested in replacing the EL Panel in the backlight, though.  Maybe I'll give that a shot.
 
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Offline GregDunn

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Re: Keithley 197A owners' corner
« Reply #55 on: September 11, 2018, 01:11:16 am »
Well... slightly premature in my previous post.  I checked the unit's AC, DC, Ω and A the first evening and all was well.  The next day, I rearranged my bench to put all the DMMs in one place and let everything warm up so I could check variance.  The Keithley started giving weird readings - the dB annunciator lit up sometimes, it showed V when reading Ω, gave a steadily increasing reading on ACV, etc.  Then I noticed the mode selector switches were sticking - this correlated with the weird readings most of the time.  My guess is that bringing the meter from its warm environment into my cool basement caused some of the lube on the switches to become more viscous.

I took the board out, tilted it so that any gunk would run out the front onto a paper towel, and hosed the switches down with 91% IPA.  Now it worked.  For a while... and then started sticking again. Repeated the procedure... exact same thing happened.  So I had to run out today and buy some high quality contact cleaner/lube.  This time I left nothing to chance; hosed the switches down, made sure nothing ran up the board into the components, let it dry, hosed it down again, repeat.  Exercised the switches in between applications.

So far (it's been on for a couple of hours) it's working at what looks to be appropriate accuracy - tracking the Fluke meters all the way up the scale on AC and DC.  I did a spot Ω check and it looked good (in fact much better than Saturday), but am going to repeat that later after I've thoroughly examined the AC/DCV ranges.

So, a question if anyone feels they can contribute: the stuff I used is a commercial product which specifically states it's a cleaner as well as a lubricant - I think it's Puretronics, which was about all they had.  Is there a need (or value) to hit the switch contacts with Deoxit after it cooks for a while?  Or should I quit now while it's working?   :-/O

Oh, in fact one more question: I took the IEEE-488 board out and left it disconnected while testing the unit.  I really don't need the capability; is there any downside to just leaving the board out and plugging the holes in the case?  I can't think of any.
« Last Edit: September 11, 2018, 01:13:06 am by GregDunn »
 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #56 on: September 11, 2018, 02:14:49 am »
... Oh, in fact one more question: I took the IEEE-488 board out and left it disconnected while testing the unit.  I really don't need the capability; is there any downside to just leaving the board out and plugging the holes in the case?  I can't think of any.

The GPIB is an option that was also sold as an upgrade kit.  Basically the modified cover and the board.  Removal should not impact the unit.  I don't think it would even make meaningful heat load difference inside the unit.

rastro

PS: the rubber buttons are a weak point for 9XX series; I've cleaned many.  ^-^
 

Offline GregDunn

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Re: Keithley 197A owners' corner
« Reply #57 on: September 11, 2018, 03:12:15 am »
I wasn't sure... it has 2 microcontrollers on the board, which is not an insignificant load; and it's stacked on top of the power supply regulator and another micro.  I may plug it back in and check the temperature rise with my IR before I button the whole thing back up.

While I had it apart I went in and cleaned the button traces on the display board.  The two I care about (dB and REL) seem to work OK.
 

Offline Cerebus

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Re: Keithley 197A owners' corner
« Reply #58 on: September 11, 2018, 02:29:14 pm »
While I had it apart I went in and cleaned the button traces on the display board.  The two I care about (dB and REL) seem to work OK.

About every other 197 I hear about has problems with that cluster of buttons until they are cleaned, mine certainly did. I suspect that should be considered a stock repair for 197s, of the kind you do as a matter of routine maintenance every time you happen to have one opened up for any reason.
Anybody got a syringe I can use to squeeze the magic smoke back into this?
 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #59 on: September 11, 2018, 03:37:11 pm »
I wasn't sure... it has 2 microcontrollers on the board, which is not an insignificant load; and it's stacked on top of the power supply regulator and another micro.  I may plug it back in and check the temperature rise with my IR before I button the whole thing back up...

The installation procedure for the GPIB option doesn't call for the instrument to be re-calibrated after field installation.  Apparently Keithley didn't feel this additional component would have a meaningful impact on system calibration.

See pdf page 53 of the manual:

http://physics.ucdavis.edu/Classes/Physics116/P116C_lab/Keithley_197AGPIB.pdf

It's not clear to me why you feel the need to remove this option.  I'd just leave it in - you may want to use it in the future.

rastro
 

Offline GregDunn

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Re: Keithley 197A owners' corner
« Reply #60 on: September 11, 2018, 05:09:42 pm »
I thought it might reduce the heating inside the case, and improve air flow.  If it's not an issue, I'll just leave it in.  Honestly, though, the chance of me ever using GPIB on an instrument are just about nil.  This is the only gear I have with that capability, for a start.   ;)
 

Offline tooki

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Re: Keithley 197A owners' corner
« Reply #61 on: September 11, 2018, 06:35:32 pm »
I would advise against removing it. You don’t want airflow!! Airflow causes temperature fluctuations and thus instability; you want everything to reach temperature and stay there. And it’s not as though these things get particularly warm anyway.

Additionally, airflow means dust or other contaminants, which you don’t want getting on the board. The high impedance circuits in this are sensitive enough to need guard traces; the last thing you want is convection airflow carrying in dust and grime and depositing it on the board.
 

Offline GregDunn

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Re: Keithley 197A owners' corner
« Reply #62 on: September 11, 2018, 06:55:36 pm »
I think you win.   :D  I did put the board on and measured some spot temps while it was cooking last night; they seemed very reasonable (max 113F at the regulator on the GPIB board) so I guess I'll leave it.

FYI and maybe of interest to the group: I cleaned the front panel switches four times with contact cleaner (yes, being ultra careful not to let any get on the board up in the sensitive analog section) and while they behaved a little better each time, there was clearly still some problem with the contacts.  I was going to give them a little Deoxit anyway, but decided to stop playing games and just squirt a minimal amount into the switches now.  It's been sitting for a few hours hooked up to a DCV source and so far it's rock solid.  Every time before, it started drifting and then jumping around by as much as tenths of a volt after a few minutes to an hour - and I had to switch modes a few times to get it to select the proper mode and settle down again.  After Deoxit, I've switched it from DCV to ACV and back, then to Ω and back, and it changed modes reliably each time.  Maybe I've gotten the last of the oxidation off the contacts.  We'll see after a little more running and some more "disturbing" the switch settings.
 

Offline GregDunn

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Re: Keithley 197A owners' corner
« Reply #63 on: September 13, 2018, 05:00:41 am »
Having already done a relative comparison of my three bench meters and found them to be very stable, I hooked them all up to a cheap AD584 voltage reference box which fortuitously came in the mail today (the KKMOON from Amazon).  I thought it might be entertaining, and it was!  My bench stayed at a very constant 24C for the 12 hours of testing, and to my surprise the Keithley read the exact values on the reference cal sheet, to the limits of its resolution, virtually from the moment it was turned on.  It wasn't a stuck reading, because I had to switch voltage outputs on the reference to get the 2.5. 5.0, 7.5 and 10.0 values.  So that was highly amusing.  The Fluke 8600 tracked perfectly, about 3mV higher, and the Dana 4200 drifted very slightly ending up about 3mV lower after a couple of hours and then not changing.

What does this mean?  I don' t know, but at the least I have 3 very stable voltmeters that are pretty good in the 0-10V range.   ;D
 

Offline GregDunn

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Re: Keithley 197A owners' corner
« Reply #64 on: September 21, 2018, 06:29:16 pm »
Going to bump this one last time for a while.  I got my second AD584-based voltage reference this week and hooked it up to the 197A.  Almost exactly spot on the listed values - just like the other reference I have.  I know that's not a confirmation that I'm in calibration, but it's a very positive result.

I'm going to order replacement electrolytic caps for this unit, to hopefully keep it alive and kicking for a few more years and forestall leakage issues.  The question: is there any reason not to replace all the caps listed below with Al-polymer units?  Except maybe the big one?  This subject seems to be discussed from time to time with no clear resolution.  For sure I'll be buying quality 105C rated parts no matter what, but I'm interested in owner's opinions.  New tantalums are likely better than the old ones, but are the polymers better still for filtering, in places where leakage is not a big deal?  I don't think any of these sit in the high impedance path.

15 µF 20V Ta [1]
10 µF 25V [4]
1500 µF 25V [1]
22 µF 16V [1]
2.2 µF 16V [1]
220 µF 25V [1]
470 µF 6.3V [1]
 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #65 on: September 21, 2018, 08:15:52 pm »
...
The question: is there any reason not to replace all the caps listed below with Al-polymer units?  Except maybe the big one?  This subject seems to be discussed from time to time with no clear resolution.  ...

I have had over a dozen K197's pass through my hands in the last 5 years.  I've never run across a leaky/bad capacitor.  As they say your "mileage may vary".  So my general approach is not to fix it if it isn't broken.  I'm sure there are many different views and experiences on this which will likely be posted...

There is no clear general answer.  Yes there are some pieces of equipment or specific boards that you do want to recap - usually they notorious and have a history of destructive failure.  For example if you just acquired a Tektronix 492 SA I would tell you to recap the SMPS - even if it's working it's probably marginal.  However from my Keithley experience I would not arbitrarily start replacing capacitors.

I don't want to discourage you from being proactive.  However you may want to consider the risk of creating problems with your rework.  For example you could create subtle problems like getting flux contamination on PCB near high impedance circuitry.  Wholesale rework could possible create cold solder joints or hairline break on a trace.  If you find a stability issue after replacing 10 items, where do you start looking?   :-//

The bottom line is you have weight the benefits.  I favor a less is better approach.  But good luck with whichever path you choose.

rastro
 

Offline technogeeky

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Re: Keithley 197A owners' corner
« Reply #66 on: September 22, 2018, 04:08:36 pm »

I have had over a dozen K197's pass through my hands in the last 5 years.  I've never run across a leaky/bad capacitor.  As they say your "mileage may vary".  So my general approach is not to fix it if it isn't broken.  I'm sure there are many different views and experiences on this which will likely be posted...


Agreed. None of my units have had bad capacitors.


There is no clear general answer.  Yes there are some pieces of equipment or specific boards that you do want to recap - usually they notorious and have a history of destructive failure.  For example if you just acquired a Tektronix 492 SA I would tell you to recap the SMPS - even if it's working it's probably marginal.  However from my Keithley experience I would not arbitrarily start replacing capacitors.

I don't want to discourage you from being proactive.  However you may want to consider the risk of creating problems with your rework.  For example you could create subtle problems like getting flux contamination on PCB near high impedance circuitry.  Wholesale rework could possible create cold solder joints or hairline break on a trace.  If you find a stability issue after replacing 10 items, where do you start looking?   :-//


I don't think that any of the electrolytic caps are anywhere near any sensitive circuitry, FYI.

It's also worth noting that the K197 is not very sensitive to pretty large voltage swings of the power rails. I know this because I supplied the voltage rails externally during a repair. I don't have advice on how this should influence capacitor replacement, but there you go.

The bottom line is you have weight the benefits.  I favor a less is better approach.  But good luck with whichever path you choose.

rastro


It's worth noting that while the warm-up time of the K197 is officially ~ 30 minutes (I think), it often settles faster. Also, internally it's a 6.5 digit multimeter ... averaged? sampled? concatenated? ... down to 5.5 digits. You can access this last digit if you have the analog output option (or if you figure out how to decipher the digital bus going to the analog board -- something I have not yet done.

 

Offline Cerebus

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Re: Keithley 197A owners' corner
« Reply #67 on: September 22, 2018, 06:03:45 pm »
Also, internally it's a 6.5 digit multimeter ... averaged? sampled? concatenated? ... down to 5.5 digits. You can access this last digit if you have the analog output option (or if you figure out how to decipher the digital bus going to the analog board -- something I have not yet done.

Erm, I think this is some half-remembered facts about another meter that you're mistakenly applying to the 197. Internally it's ±220,000 count, not 61/2 digits by any stretch of the imagination. The analogue output is ±4V in 1mV steps (derived from a 13 bit DAC) - there is no way that would provide access to any extended precision, even it if was there to be had.
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Offline GregDunn

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Re: Keithley 197A owners' corner
« Reply #68 on: September 22, 2018, 06:32:07 pm »
The consensus, then, seems to be that the caps don't automatically need replacing on these.  I'm totally OK with this - I was just concerned because so many people have experienced leaky Al electrolytics or dying Ta caps on HP, Fluke, etc. meters which can cause damage to the boards.  But if that's not endemic to these meters, I'll settle for measuring the power supply voltages next time I have it open and doing a good visual scan for bulging or leaky caps.

On an unrelated note: where is the serial number supposed to be on these?  I have no external stickers and saw nothing that looks like a serial inside the case - just board model designations.  I'm thinking there should be a sticker and it's peeled off in ages past, but since this is the only one I've ever used...

 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #69 on: September 22, 2018, 07:47:50 pm »
On an unrelated note: where is the serial number supposed to be on these?  I have no external stickers and saw nothing that looks like a serial inside the case - just board model designations.  I'm thinking there should be a sticker and it's peeled off in ages past, but since this is the only one I've ever used...

If it's not on the rear of the unit it's probably lost - I've seen a few with missing S/N's. 

When I get a new piece of test equipment I usually check the fuse values.  On the K197(A) the mains fuse is only accessible with case open.  The factory fuses are glass cartridges that have a resistor in them.  I've also never seen one of these replaced.  The other fuse is the 2A fast-blow for amp-function it is assailable at the front .  Now I have seen wrong values arrive on the 2A fuse.

10A Current Function:
You may ask where is the 10A fuse but there is none on the standard K197/197A DMM's.  So I would keep this in mind should you decide to use the 10A measurement function.  I probably would find another meter to measure anything above 2A.  The K197M(ilitary) as previously mentioned does have the 10A fuse at the main board.  I also would advise against fudging in a 10A fuse on the board. 

rastro
« Last Edit: September 22, 2018, 07:51:04 pm by rastro »
 
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Offline Aleks

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Re: Keithley 197A owners' corner
« Reply #70 on: May 04, 2019, 07:47:19 pm »
Hi all,

The mailman delivered a 197A today, that I got for a bargain (32EUR). The unit has the display half working, which I thought would be an easy fix. Upon closer inspection, I've seen that the LCD zebra strips have warped and they are not making contact PCB <-> LCD any more.

I'd guess that sourcing these would be next to impossible these days, but someone might have an idea about finding some similar zebra strips?

Oh, and I can spot one bulged capacitor on my unit (on the GPIB PCB), so, maybe that would be a first in this thread :-)

Cheers!
 

Offline Aleks

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Re: Keithley 197A owners' corner
« Reply #71 on: May 04, 2019, 09:55:03 pm »
Luckily after a second look, it turned out that the zebra strips were not (maybe the only?) problem! For some reason, the underlying EL strip (which was dead) was placed at an angle, so it was obstructing the LCD plastic bezel in making contact with the PCB. This in turn did not let the zebra strip mate with the PCB on the upper left side of the LCD.

The fix: I removed the EL strip, would be making a fix with a generic EL strip from fleabay, for starters, then I saw that due to the stress that was present on the LCD, the black/gray paper filler inside the plastic bezel was indented. In order to fill up the space I made a spacer with some sticky notes that I cut in the shape of the bezel plastic. I used sticky notes so that I can remove layer by layer until I find the optimum pressure.

After reassembling the LCD, I was greeted with all zeros on the display! To verify I kept pressing the "dB" button while powering up the meter and saw that all segments were working!

Next would be for me to replace the bulged cap, hunt for a EL replacement and verify/calibrate the thing.

The 197A will make a nice addition to my bench, next or on top of my Keithley 199
 

Offline tooki

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Re: Keithley 197A owners' corner
« Reply #72 on: May 05, 2019, 06:54:49 am »
Nice!

This reminds me, I really should get back onto my project of designing a replacement display PCB for these, since a bright LED or OLED display would be so much easier to read. I've already tested the arduino code others have written to decode the data bus to the display, and it works fine, so it really is just down to actually designing a display board...
 

Offline Aleks

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Re: Keithley 197A owners' corner
« Reply #73 on: May 05, 2019, 11:38:17 am »
I've read couple of posts regarding that, hope that you find time for it! I saw a post dating from 2014 about member timb finding an OLED display that is the same size as the original LCD, was the display/part number ever found ?

 

Offline tooki

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Re: Keithley 197A owners' corner
« Reply #74 on: May 06, 2019, 12:11:47 pm »
I don't think he ever replied. :(
 

Offline Kinkless Tetrode

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Re: Keithley 197A owners' corner
« Reply #75 on: June 16, 2019, 09:47:37 am »
Hi all, I'm a new proud owner of a couple the Keithley 197 (Military Version AN/USM-486A) units.  I bought them from a seller who must have got them from a military surplus auction, and other than some desert dust on them, they are both in great condition.  I don't know if and when they were last calibrated, but the two units read very closely to each other; within about 10 mV on the 200 mV range.

Does anybody have any idea how common this military model is compared to the regular 197/A models?  Or, how long they were in production?  Other than the references given earlier in this thread, I really don't see anything mentioned about them on the internet.

Thanks.
« Last Edit: June 16, 2019, 10:06:36 am by Kinkless Tetrode »
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Offline rastro

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Re: Keithley 197A owners' corner
« Reply #76 on: June 16, 2019, 02:36:29 pm »
...
Does anybody have any idea how common this military model is compared to the regular 197/A models?  Or, how long they were in production?  Other than the references given earlier in this thread, I really don't see anything mentioned about them on the internet.

Thanks.

Congratulations on your purchase. 

I am not sure about the history of the 197 line but here are some observations:
- Based on the technology the military model came out after the original 197/A models
- The 197M(AN/USM-486A) shows a date of December 1994.
- Last year I came across two 197A models that did not have back light but had the new processor like the military mother board but without the 10A current fuse.  Date on the that motherboard was 1992.
- I bought my initial 4 military models about 5 years ago new old stock from an auction house - this was an uncommon find at the time.
- In the last 2 years I've seen more military models showing up on ebay; usually new/lightly used.  Probably the US govt getting around to purging old stock.

Anyway I think the military model is the best choice if you don't need the back-light or GPIB option.

rastro

« Last Edit: June 16, 2019, 02:39:29 pm by rastro »
 

Offline Kinkless Tetrode

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Re: Keithley 197A owners' corner
« Reply #77 on: June 16, 2019, 10:05:17 pm »
...
Does anybody have any idea how common this military model is compared to the regular 197/A models?  Or, how long they were in production?  Other than the references given earlier in this thread, I really don't see anything mentioned about them on the internet.

Thanks.

Congratulations on your purchase. 

I am not sure about the history of the 197 line but here are some observations:
- Based on the technology the military model came out after the original 197/A models
- The 197M(AN/USM-486A) shows a date of December 1994.
- Last year I came across two 197A models that did not have back light but had the new processor like the military mother board but without the 10A current fuse.  Date on the that motherboard was 1992.
- I bought my initial 4 military models about 5 years ago new old stock from an auction house - this was an uncommon find at the time.
- In the last 2 years I've seen more military models showing up on ebay; usually new/lightly used.  Probably the US govt getting around to purging old stock.

Anyway I think the military model is the best choice if you don't need the back-light or GPIB option.

rastro




Rastro, Thanks for your insightful observations.

Also, I notice that on the bottom of our units there is some US Gov't contract information. My unit says "contract daah01-92d-0031" and since gov't contracts are public information, we might be able to get a bit more information on the 197-M series from government archives.  Hmm...this makes me very curious...

A Google hit shows that an M model, with case and probes, was sold on eBay late last year for $360.  So it looks like there are a few floating around. And I completely agree, it's a really great portable/bench 5.5 digit unit.  I really like the extra shielding and toroid upgrade.

KT
« Last Edit: June 16, 2019, 10:27:25 pm by Kinkless Tetrode »
Whilst others count beans, I count electrons, and photons too.
 

Offline Brian of Romsey

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Re: Keithley 197A owners' corner
« Reply #78 on: July 22, 2019, 11:05:39 pm »
Re: Replacement display technology.

I have been pondering this today.  I would assert that there are no suitable OLED displays easily available.  There are tiny ones but nothing with the sort of size needed to replace the existing display.

There also don't seem to be any TFT LCDs with the right sort of aspect ratio.  By the time you get to something wide enough, they are way too tall for the case and also getting quite expensive.

It's my opinion that the best replacement is LED displays.  But even this is hard and by no means perfect.  The readout needs a small text field on the left (Auto, Rel, dB, Stor, Recl, Bat, etc), a 7-segment numeric field for the value, including a leading minus sign (seven displays), and a small text field on the right (multiplier, units, and maybe "AC").  I think that the text fields can be handled by 5x7 displays.  Either two VQC10, two HDSP-2000, or eight TIL305 displays.  Maybe even HDSP-2113.



 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #79 on: July 23, 2019, 01:08:25 am »
Re: Replacement display technology.

I have been pondering this today.  I would assert that there are no suitable OLED displays easily available.  There are tiny ones but nothing with the sort of size needed to replace the existing display.

There also don't seem to be any TFT LCDs with the right sort of aspect ratio.  By the time you get to something wide enough, they are way too tall for the case and also getting quite expensive.

It's my opinion that the best replacement is LED displays.  But even this is hard and by no means perfect.  The readout needs a small text field on the left (Auto, Rel, dB, Stor, Recl, Bat, etc), a 7-segment numeric field for the value, including a leading minus sign (seven displays), and a small text field on the right (multiplier, units, and maybe "AC").  I think that the text fields can be handled by 5x7 displays.  Either two VQC10, two HDSP-2000, or eight TIL305 displays.  Maybe even HDSP-2113.

Yes it's difficult to find a good functional fit to replace the old LCD display.
I believe several of the display suggested are obsolete or difficult to readily source (VQC10, HDSP-2000, TIL305).
You also need to consider part costs.  The HDSP-2113 is available but in small quantities costs $37.00 from mouser.

Dave Jones did a thread/video on making custom LCD's.  This could be a direct replacement for a leaky/broken LCD.  The difficulty is there is a fair amount of up front setup costs and design effort to duplicate a replacement.  You would need to get enough sponsors sharing the cost to make this route feasible.  Then there is also the problem of getting new zebra connectors to replace 30 year old ones just hanging on.  Probably not going to get off the ground.

Another solution I thought about is making a PCB that replaces the current display board (same size) but has SMD LEDs replacing the LCD along with a plastic template/screen for symbols/words.  Getting the double sided (?) PCB produced in small quantities would be reasonable.  However soldering all those SMD LEDs would be certainly be a labor of love.  However I think this would be the cleanest and most attainable solution.  It would also upgrade the K197(brown) to better viewing than a K197A(grey) with LCD/back-lighting.  Lot's of work on PCB design routing the drivers and probably programing a controller for display generation.  Once complete it could also be adapted for other Keithleys of that series.  Wish I had time to start something like this...

rasto
 

Offline Brian of Romsey

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Re: Keithley 197A owners' corner
« Reply #80 on: July 23, 2019, 07:52:29 pm »
Rasto,

  I agree on the price of things for an in-case solution.  Perhaps an out-of-case solution would work with some sort of new display, probably a 3.5" TFT LCD in a little case with a cable to the 197A.  Portrait mode, status indicators at the top, big numerical value right across with units at the right, and then maybe an analogue 'meter' at the bottom.

      https://www.aliexpress.com/item/32609807497.html?spm=a2g0o.productlist.0.0.1b7a5e359o85W8&algo_pvid=6e1ec20b-de25-421a-91cc-a95b11ceb965&algo_expid=6e1ec20b-de25-421a-91cc-a95b11ceb965-6&btsid=42aa5706-d76b-47e8-9567-bc3062ca7320&ws_ab_test=searchweb0_0%2Csearchweb201602_6%2Csearchweb201603_52

  The other (remote) possibility for the in-case solution is whether a couple of these:

      https://www.aliexpress.com/item/32801200578.html?spm=a2g0o.productlist.0.0.5e9b3b27Vdioca&s=p

could be brought close enough together horizontally and made to work.

  Cheers, Brian.

 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #81 on: July 23, 2019, 09:12:41 pm »

Maybe extend the out-of-case-display concept using an ESP8266/ESP32 to extract the readings/status from the K197 and use the WIFI to access a simple server on the module displaying the DMM data.  Then you have an unlimited choice of WIFI connected displays (phone/tablet/PC).  I think you can get an ESP8266 for under $5.00.

I'm not an expert on the ESP's but it seems feasible according to other projects I have seen using these modules. 

rastro
 

Offline Brian of Romsey

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Re: Keithley 197A owners' corner
« Reply #82 on: July 23, 2019, 10:24:25 pm »
Hi,

The idea of Wi-Fi or Bluetooth and an ESP had occurred to me.  I hadn't thought of an internal webserver to be honest.

I am aware that there are existing (modern) DMMs and such like that do some sort of BT protocol for remote displays.  Given how much trouble Dave reported getting the BT thing working with his recent DMM I figured that that was a path to a whole heap of pain.

Cheers, Brian.
 

Offline Brian of Romsey

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Re: Keithley 197A owners' corner
« Reply #83 on: August 10, 2019, 07:33:55 pm »
Hi,

  Found a possible SPI OLED display: https://www.aliexpress.com/item/32988174566.html

  With a resolution of 256 by 64 that would be sufficient for sign, value, & units in the top third of the display and all the rest of the possible status bits and bobs along the bottom third.

  Cheers, Brian.
 

Offline Brian of Romsey

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Re: Keithley 197A owners' corner
« Reply #84 on: August 12, 2019, 12:59:19 pm »
Hi,

This is an instrument display replacement strategy.  It may be instructive for a 197 or 197A display replacement.

Brian.
 

Offline electrold

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Re: Keithley 197A owners' corner
« Reply #85 on: September 13, 2019, 06:01:15 pm »
     I just received the AN/USM-486A military model of the Keithley 197 multimeter which I purchased on eBay. It came with its carrying case, IEC line cord, test leads, and RF probe. It has the battery and looks new. It powered up fine and some preliminary checks give me confidence that it will perform as it should. This model has the battery option and the rear panel CALIBRATION switch.
      One thing I observed from reading the military manual and the Keitlley manual is that the military model has relaxed accuracy specs. For example, the Keithley 197 spec for the 2VDC range is 0.011% +2 counts for 1 year, whereas the military spec is 0.05% +10counts for 1 year. Other specs are similar with the Kiethley having the better specs. I don't know if the Keithley model is actually better or if the military has just loosened their required specs. If anyone has any knowledge about this I would appreciate a reply.
 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #86 on: September 13, 2019, 10:04:20 pm »
I haven't dug into it, but did you take in account for the environmental range expectation on the "M" version?
 

Offline electrold

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Re: Keithley 197A owners' corner
« Reply #87 on: September 14, 2019, 11:36:41 am »
Environmental specs are identical on commercial and military versions according to the manuals. I do find a difference in warm-up times though. The commercial 197 has 1 hour warm-up to rated accuracy but the military 197M has a warm-up time of 5 minutes. Perhaps this is the reason for the relaxed accuracy spec on the 197M. If it is operated on battery, you can't wait around for an hour for it to settle down to the better accuracy.
 

Offline rastro

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Re: Keithley 197A owners' corner
« Reply #88 on: September 14, 2019, 02:41:54 pm »
You're probably right about the 5-minute warm up needing 'relaxed' specifications.  Most likely the 'M' version is probably on par with the standard K197 if you allow a full hour warm up.

As mentioned before I still prefer the 'M' version because it has an added fuse on the 10 Amp input and removable power cord.  It also looks like it has better noise shielding.

rastro
 

Offline electrold

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Re: Keithley 197A owners' corner
« Reply #89 on: September 14, 2019, 04:23:18 pm »
The battery in my meter was, of course, discharged and could not be charged as 5 of the 10 cells in the pack were unchargeable. Who needs battery operation for this anyhow? Certainly I don't - so I removed the pack and the battery board.
My meter has a CAL sticker on it - it was last calibrated Dec 2, 2016 and has a cal void date of Mar 22, 2019. Using my A584-M Voltage Reference Module with the meter warmed up for more than an hour, it is well within the 197 commercial specs, at least at 2.5, 5, 7.5, and 10VDC.
 


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