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.Oh, nice.
I have been building the equipment I need to test and repair them recently, so I should be fixing them soon.
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.Oh, nice.
I have been building the equipment I need to test and repair them recently, so I should be fixing them soon.
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.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.Oh, nice.
I have been building the equipment I need to test and repair them recently, so I should be fixing them soon.
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?
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.
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.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.
There is also a 197 Military version. Which is an uplift on the standard 197 model.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.)
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 (http://www.liberatedmanuals.com/TM-11-6625-3055-24P.pdf)
There is also a 197 Military version. Which is an uplift on the standard 197 model.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.)
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 (http://www.liberatedmanuals.com/TM-11-6625-3055-24P.pdf)
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
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 (https://groups.io/g/TekScopes/topic/jfet_needed_for_range/966846?p=Created,,,20,1,20,0)
...I'll take a look. I might take a few days since I'm in the middle of replacing my work bench.
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 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.
... 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
197M tear down...additional pictures.
...
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.)
...
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 (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
...I'll take a look. I might take a few days since I'm in the middle of replacing my work bench.
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).
-rastro
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.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.
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
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 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 (https://github.com/technogeeky/keithley-197). 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.
/* 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/* 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 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 (https://github.com/technogeeky/keithley-197). 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
andCode: [Select](I changed the colors to my wires :P)/* 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 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. :)
... 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.
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.
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 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
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.
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...
...
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.
...
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
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.
That's quite a lovely site... :)
Please help!Do not cross-post. As I said in the other thread, with a new question, you should be starting a new thread anyway.
I just got a Keithley 197A from a seller on eBay.com and it is clearly defective! The seller will not take a return so I may have to try and fix this bugger! I have a little bit of experience with this and only have an oscilloscope and a multimeter to work with. Here is a Youtube video of what the unit is doing. Do you think there is any hope?
https://youtu.be/6OrLtb9O-co
Thanks!
Zac
... Stuff Elided ...
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.
... More Stuff Elided ...
I have now reversed engineered the way the voltmeter talk to the IEEE-488 card: https://www.eevblog.com/forum/projects/reverse-engineering-of-the-internal-ieee-interface-of-the-keithley-197a/msg5202936/#msg5202936 (https://www.eevblog.com/forum/projects/reverse-engineering-of-the-internal-ieee-interface-of-the-keithley-197a/msg5202936/#msg5202936)
I found the printed Instruction manual for the "Model 1973/1973 IEEE-488" for the Keithley 197", including schematics. Now lying here on my desk.
No time for scanning at the moment, will do it in the winterholidays and post it here.
If I should look into something detailed send a PM
mk_
Hi all,
I hope can find some help here.
I've a Keithley 197 which shows an always positive drift on the last 2~3 digits, It's seems to stop after ~1 hour if I don't touch any of the front panel controls.
This happens on any range.
I've started to do check of internal nodes and the only weird thing I've found is -V node at -14.5V, it's showing ~200mv of 100hz rectifier cap ripple. This node, from schematic, should be -15V see R132 and VR105 (which should be a 15V zener)
R132 is at nominal value and VR105 was tested good, so I guess there is some unexpected current request from -15V that is able to bring the node too low to make VR105 work.
All other voltages seems clean and at nominal value (-9V, -6.4V, +5V A and D, +10V)
Moreover I've was not able to spot any issue in the measure path or A/D waveform.
Please let me know if -V is expected to be -15V & clean, and any of your thoughts on this issue.
Regards,
Fabio I.