Test Equipment Anonymous (TEA) group therapy thread

[bitseeker]

That noise deserves this smiley

[0culus]

Did a partial teardown of the 3455A today. I didn't actually take anything apart, rather just looking over the innards to make sure nothing obviously amiss. The button freeing job is going to have to be done in a cat free environment.  Just taking a peek under the hood, so to speak. It is *super* clean inside! It is equipped with the AC RMS module. Literally no evidence of tampering [edit] on the boards inside. One thing I took a look at in light of the exploding line filter in that other thread was the line filter. I don't think it's the explodey kind? It's labeled "CORCOM" and says it's made in Mexico. I dunno if that would be original or not. According to the serial number this is a 1977 unit.

[edit] not pictured is the cover of the analog section before I removed the strap that protects the calibration ports.

Bonus pic of both my trusty Fluke 87-V and the 3455A measuring output from my DC supply, and agreeing exactly!

[tggzzz]

That noise deserves this smiley

That comment deserves showing how you can use a saturated Weston standard cell as a thermometer:

• 1500 samples/day, so about 3 days record
• saturated cell has a 40uV/C tempco
• note the relative lack of noise compared to the zener

[grizewald]

The 7075 lives! It ain't perfect, but it's not far off either.

The root cause of the problem was as expected:





It really, really helps if the digital logic actually gets data and can pass it on to the memory and counters!

It took absolutely ages for the meter to warm up to a stable internal reference voltage. I had the fire extinguisher on the bench at the ready as both the 7075 and the Thurlby supply are unknown quantities! After close on two hours, the internal reference stopped increasing in voltage and settled down to 6.999413V (varying +/- 2uV from 411 to 415).

Once I'd got a stable reference, I ran the self tests:

Test 1 (Internal Reference) Should be: 7V +/- 0.005V is: 6.999413 PASS!!
Test 2 (A-D Internal Zero) Should be: 0V +/- 0.0002V is: -0.000280 FAIL (just)
Test 3 (AC Converter) Should be: 10V AC +/- 0.01V    is: 10.0002 SUPER PASS!!
Test 4 (Ohms Converter) Should be: 10.000R +/- 0.02K is: 10.003780K FAIL

So, voltage looks reasonable, but ohms is a little high. I turned to my simple references.

First I checked shorted probes on the voltage range:



Looks OK!

Then, my Fisher Electronics LT1021 reference, which was calibrated at 10.00002V and had been powered on since I powered on the meter:



That's a FAIL.

Then I plugged in my (hardly) Kelvin clips and shorted them:



Promising...

Some Vishay precision metal foil resistors - 5K00000 and 10K0000 at 0.005% tolerance:



FAIL - too high



Also FAIL - too high

Then a Vishay 23K524 at 0.1% resistor:



Pass!

And finally, a Bourns 1R0 at 0.1%



Pass!

All, in all; a bit of a mixed bag.

There's lots of cleaning to be done. Particularly all the copper springs which should connect the case panels to the meter's ground. I doubt that they make anything more than a spectacularly bad connection at the moment considering how tarnished they are.

My test leads are far from optimal - the connections into the Fischer plug are white bootlace ferrules which have a reasonably good fit once they are crimped, but they're nickel plated copper. My Kelvin clips are just simple crocodile clips with both wires connected at the screw on the longest arm.

Even so, the voltage and resistance differences from what is expected are too large to be caused by my crappy test leads. So, it's not quite a "winner, winner, chicken dinner", but I think it'll come good with some more fettling.

It is worth getting hold of the 7081 operating manual and having a look at section 3, "warm-up procedure after prolonged low-temperature storage". My 7081's stability certainly improved after self-cooking for several days.

Thanks for that tip, I'll go and study that. At least I have some time over the weekend to be with the meter while it's on. I've no idea of the condition of the mains filter and I won't be leaving it turned on without oversight for some time.

And "get a reference" is a vast topic in its own right T'aint as easy as going out and buying one, unless you have lots of cash to spare plus (for some options) space and load-bearing capacity

Yeah, I'm painfully aware of the depths of volt-nuttery I've exposed myself to by getting a 7.5 digit capable meter. It's a very deep and very expensive hole...

Even so, the voltage reference comes with a calibration sticker and the voltage was measured with a calibrated meter. The Vishay resistors should be within a reasonable distance of their original tolerance and I'm not even close on either, so there's certainly more work to be done.

[med6753]

Holy crap...good work!  My volt-nuttery is holding steady at 5.5 digits. And I think for now it will remain there. If I go down that 6.5 or 7.5 rabbit hole I may never come out. 

[mnementh]

Welcome to my Winter Wonderland. Much too early for this shit. And it started snowing again. 

Looks like home... *Wistful sigh*   

mnem
I miss "weather".

I'll send you some. Check your mailbox. 

              *Sigh...*

The 10 Laws of TEA (and counting) :

1 )  TE will expand to fill all space available. And then some.   (SNIP)

Added to the OP.

Suh-WEET! 

   Here's what I woke up to on the bench this morning over my first cuppa coffee... kinda the inverse function thereof. Once the deed was done, I had to be elsewhere for a while.   
Maybe a better title would be Chaos Theory? Dinner Conversation? Politics?   

TEA with Spaghetti

   Alas, I've already done a piece titled "Spaghetti with Motorballs"; I wouldn't want to be too derivative.

OK, TEA Mein, then.

Oooh... good idea. Test Lead Lo Mein it is!   

Holy crap...good work!  My volt-nuttery is holding steady at 5.5 digits. And I think for now it will remain there. If I go down that 6.5 or 7.5 rabbit hole I may never come out. 

I'm with you med...

I don't feel a need to be able to measure any voltage smaller than I can generate across the fillings in my own mouth.

mnem
*TEA-compliant*

[mnementh]

Taste the Rainbow, Bizzitches...



Very pleased with the end result; they turned out better than I hoped. The stacking ends solder up easily, are very easy to assemble, the sheaths move smoothly and when released they close with a very satisfying snap. On my HP 3478A, they get ~4mm of contact; not optimal, but just enough to not pop out on their own and certainly still serviceable. On my other meters they get ~5.5mm contact, which is the same as the molded ends. The lantern springs ride snug on the pin which is machined, not cast like some of the cheap ones, so they make good contact internally. 

The twelve 13ga leads are ~0.66m long, the two 12ga green leads are each 1m long. I went for 12ga on those just to see if you can cram that large a wire in these ends; you can, and they don't need to be modified, but you need to get the angle just right on the wire when soldering, and be very careful when assembling the endcap to get it aligned square and centered on the pin before pressing it into place.



Total cost, including the green 12ga silicone wire from BG, approx $40.

https://www.aliexpress.com/item/TL320-12pcs-lot-R-B-1-0meter-High-Quality-13AWG-flexible-silicone-test-leads-4mm-straight/32681958679.html

https://www.aliexpress.com/item/50pcs-5color-Gold-Plated-Retractable-4mm-Stackable-Plug-Soldering-Type/1781741357.html

Cheers,

mnem
ZZZzzzZZZzzzZZZzzz...

[tautech]

Solder-ily nice job mnem. 



Granddad mode again, CJ and his mum and dad are here for the weekend.

Quite a little character.

[Brumby]

Here's what I woke up to on the bench this morning over my first cuppa coffee... kinda the inverse function thereof. Once the deed was done, I had to be elsewhere for a while.   

Maybe a better title would be Chaos Theory? Dinner Conversation? Politics?   

TEA with Spaghetti

Think I'll go with quantum entanglement.

[tggzzz]

The 7075 lives! It ain't perfect, but it's not far off either.

Then, my Fisher Electronics LT1021 reference, which was calibrated at 10.00002V and had been powered on since I powered on the meter:
Some Vishay precision metal foil resistors - 5K00000 and 10K0000 at 0.005% tolerance:
All, in all; a bit of a mixed bag.

Good stuff

The references are a good start, but eventually you will want to measure their drift with temp and time, heh, heh, heh. (I always liked Muttley!)

There's lots of cleaning to be done. Particularly all the copper springs which should connect the case panels to the meter's ground. I doubt that they make anything more than a spectacularly bad connection at the moment considering how tarnished they are.

Cleaning is an interesting topic, especially w.r.t. PCBs: will you do more harm than good?

My test leads are far from optimal - the connections into the Fischer plug are white bootlace ferrules which have a reasonably good fit once they are crimped, but they're nickel plated copper.

I used that technique for my 7081, with them spaced by a PTFE carrier mounted in a body made from copper pipe. I was going to replace the ferrules with the shank of some pogo pins (possiblyu gold plated), but then I splurged on a pair of the proper Fischer connectors - which cost noticeably more than the 7081 itself!

Even so, the voltage and resistance differences from what is expected are too large to be caused by my crappy test leads. So, it's not quite a "winner, winner, chicken dinner", but I think it'll come good with some more fettling.

Yeah, I'm painfully aware of the depths of volt-nuttery I've exposed myself to by getting a 7.5 digit capable meter. It's a very deep and very expensive hole...

Even so, the voltage reference comes with a calibration sticker and the voltage was measured with a calibrated meter. The Vishay resistors should be within a reasonable distance of their original tolerance and I'm not even close on either, so there's certainly more work to be done.

With patience and obsessive scouring of fleabay and auction sites, you can find high quality stuff at tolerable prices. My 10V references (one since measured as 9.999571V at the Hannover Maker Faire) and Guildline resistors cost £15 each, my 7-decade KVD £180.

Before fettling internally, do replace the mains filter and recap the PSU, and leave the thing on for several weeks.

[bd139]

Random thing of TEA interest. I was going through the "cupboard of doom" this morning to find some stuff to shift and the box for my DG1022Z and I found an interesting book I forgot I had. Probably bought this in the mid 1980s before I found a cheap scope to get my mits on.



Turns out there is a PDF version here: https://www.americanradiohistory.com/Archive-Bookshelf/Author-Groups/Bernards%20Radio%20Manuals/Babani-BP57-How-to-Build-Your-Own-Solid-State-Oscilloscope.pdf

Also found a 1st edition copy of Zen and The Art of Motorcycle Maintenance.

[med6753]

I remember that book and I think it's part of what was called “TAB” publishing here and I have several  of their books but not that one. I also have many of the Gernsback volumes going back to the 1950's which were my Father's. But the most valuable of the old books in my library is this puppy from 1970. 672 pages of hollow state goodness and the absolute zenith of vacuum tube technology. It's hard to believe in about 10 years after that they went bust.   

[tggzzz]

Once I'd got a stable reference, I ran the self tests:

Test 1 (Internal Reference) Should be: 7V +/- 0.005V is: 6.999413 PASS!!
Test 2 (A-D Internal Zero) Should be: 0V +/- 0.0002V is: -0.000280 FAIL (just)
Test 3 (AC Converter) Should be: 10V AC +/- 0.01V    is: 10.0002 SUPER PASS!!
Test 4 (Ohms Converter) Should be: 10.000R +/- 0.02K is: 10.003780K FAIL

I regard those as sanity checks, no more. After all, they are all using a reference voltage to measure things derived from that same reference voltage.

Don't forget to look at the AC voltage with shorted inputs. It should be zero, but on several of my meters it is far from that! the AC to DC converter is, of course, separate and to blame - look at the specs and there is a significant difference compared to the DC specs.

[grizewald]

Good stuff

The references are a good start, but eventually you will want to measure their drift with temp and time, heh, heh, heh. (I always liked Muttley!)

The small shame with the 7075 is the "Parallel BCD Interface". I can't imagine that there are any PC interfaces for it, so I guess I'll have to roll my own with an Arduino to get some logging functionality from the meter. It did come with the interface unit which bolts on the back, so I have half of the puzzle at least.

Cleaning is an interesting topic, especially w.r.t. PCBs: will you do more harm than good?

There's a fair layer of dust and grime on the upper two of the analogue boards and as I say, I spotted some rust spots on some metal cans on the lower board, but have not inspected the lower board fully. Grime means leakage on something this sensitive, so some gentle washing with iso may be warranted to fend off future issues.

I also had a look at the 7081 manual as you recommended. As I don't have a packing case or anything like that, I've placed the meter flat on my antistatic mat to cover the bottom air holes and have covered the upper air holes after sticking a thermocouple just inside the top of the case. It's currently cooking at 37C! (I'll abort if it goes over 40C, just in case.)

I used that technique for my 7081, with them spaced by a PTFE carrier mounted in a body made from copper pipe. I was going to replace the ferrules with the shank of some pogo pins (possiblyu gold plated), but then I splurged on a pair of the proper Fischer connectors - which cost noticeably more than the 7081 itself!

I saw your masterful DIY Fischer connector. Very nice indeed!

I think that what I'll do is order some of AB Precision's 4 core shielded PTFE cable and retrofit the meter with the Lemo connectors I found on Mouser. Then I can make up two cables (one for voltage and one for resistance with Kelvin clips) with equivalent performance to the ones originally supplied by Solartron. Pay day needs to come around first though.

With patience and obsessive scouring of fleabay and auction sites, you can find high quality stuff at tolerable prices. My 10V references (one since measured as 9.999571V at the Hannover Maker Faire) and Guildline resistors cost £15 each, my 7-decade KVD £180.

Before fettling internally, do replace the mains filter and recap the PSU, and leave the thing on for several weeks.

I'm currently in eBay ninja mode for a KVD. "Hens teeth" is the phrase that springs to mind, especially here in Europe. I have to admit to a bad attack of jealousy regarding our American friends and the vast array of test kit available to them at reasonable prices in comparison to the overpriced and limited choices from EU sellers. Importing stuff from outside the EU is currently a joke here in Sweden with the postal service inflicting delays of several months on all imported items. Even if that wasn't an issue, the fact that most US sellers quote shipping charges which double or triple the price of the equipment makes buying from the US an non-starter for me.

Until the magic day when I find a Fluke divider at a less than bank balance destroying price, I'm currently planning to build a Hamon divider to provide me with a larger range of voltages, plus keeping an eye out for a bridge while I'm at it.

[grizewald]

Once I'd got a stable reference, I ran the self tests:

Test 1 (Internal Reference) Should be: 7V +/- 0.005V is: 6.999413 PASS!!
Test 2 (A-D Internal Zero) Should be: 0V +/- 0.0002V is: -0.000280 FAIL (just)
Test 3 (AC Converter) Should be: 10V AC +/- 0.01V    is: 10.0002 SUPER PASS!!
Test 4 (Ohms Converter) Should be: 10.000R +/- 0.02K is: 10.003780K FAIL

I regard those as sanity checks, no more. After all, they are all using a reference voltage to measure things derived from that same reference voltage.

Don't forget to look at the AC voltage with shorted inputs. It should be zero, but on several of my meters it is far from that! the AC to DC converter is, of course, separate and to blame - look at the specs and there is a significant difference compared to the DC specs.

I'm currently getting 0.000236V with shorted inputs on AC. Good or bad?

[capt bullshot]

This HP kit looks nice inside.
For comparison, my latest TEA addition: https://cb.wunderkis.de/wk/AC-Source-EAC/teardown/

Still have to figure out how to operate the thing, it doesn't have any controls, everything via RS232, no description or manual nor software available. Manufacturer has still to answer my email, wonder if they'll ever do. About the same time this thing was manufactured (1990 ... 2000), I've worked for a small company, the boss would have declined support for a long time out of production unit.

Well, I know where they are sited. If they don't answer, we can molest them personally.

Okay, it's just about 160km from me

[tggzzz]

Once I'd got a stable reference, I ran the self tests:

Test 1 (Internal Reference) Should be: 7V +/- 0.005V is: 6.999413 PASS!!
Test 2 (A-D Internal Zero) Should be: 0V +/- 0.0002V is: -0.000280 FAIL (just)
Test 3 (AC Converter) Should be: 10V AC +/- 0.01V    is: 10.0002 SUPER PASS!!
Test 4 (Ohms Converter) Should be: 10.000R +/- 0.02K is: 10.003780K FAIL

I regard those as sanity checks, no more. After all, they are all using a reference voltage to measure things derived from that same reference voltage.

Don't forget to look at the AC voltage with shorted inputs. It should be zero, but on several of my meters it is far from that! the AC to DC converter is, of course, separate and to blame - look at the specs and there is a significant difference compared to the DC specs.

I'm currently getting 0.000236V with shorted inputs on AC. Good or bad?

Yes

That's similar to the value I saw. I've tweaked just about everything on one of my 7075s, and I especially tweaked that to be ~1uV. However, I have not verified that was the correct decision; time will tell. One issue is that my AC "reference" source is very crude: an ancient HP analogue function generator where I measure the peak voltage of a 0.001Hz signal and hope it is the same at 1kHz. Necessity  is the mother of invention.

[tggzzz]

The small shame with the 7075 is the "Parallel BCD Interface". I can't imagine that there are any PC interfaces for it, so I guess I'll have to roll my own with an Arduino to get some logging functionality from the meter. It did come with the interface unit which bolts on the back, so I have half of the puzzle at least.

That's one option, a simple logic analyser would be another.

I also had a look at the 7081 manual as you recommended. As I don't have a packing case or anything like that, I've placed the meter flat on my antistatic mat to cover the bottom air holes and have covered the upper air holes after sticking a thermocouple just inside the top of the case. It's currently cooking at 37C! (I'll abort if it goes over 40C, just in case.)

I used a blanket, but the temperature is what matters.

I saw your masterful DIY Fischer connector. Very nice indeed!

I don't remember posting a picture of my bodged 7081 connector. Since it is made of two diameters of copper plumbing pipe and heatshrink, I would prefer to call it "hillbilly" or "Heath Robinson" rather than "masterful"!

I think that what I'll do is order some of AB Precision's 4 core shielded PTFE cable and retrofit the meter with the Lemo connectors I found on Mouser. Then I can make up two cables (one for voltage and one for resistance with Kelvin clips) with equivalent performance to the ones originally supplied by Solartron. Pay day needs to come around first though.

I think those PTFE cables are a good option.

I used some https://www.ebay.co.uk/itm/253173432482 but I wouldn't go so far as to recommend it since it needs added mechanical protection.

I'm currently in eBay ninja mode for a KVD. "Hens teeth" is the phrase that springs to mind, especially here in Europe. I have to admit to a bad attack of jealousy regarding our American friends and the vast array of test kit available to them at reasonable prices in comparison to the overpriced and limited choices from EU sellers. Importing stuff from outside the EU is currently a joke here in Sweden with the postal service inflicting delays of several months on all imported items. Even if that wasn't an issue, the fact that most US sellers quote shipping charges which double or triple the price of the equipment makes buying from the US an non-starter for me.

Until the magic day when I find a Fluke divider at a less than bank balance destroying price, I'm currently planning to build a Hamon divider to provide me with a larger range of voltages, plus keeping an eye out for a bridge while I'm at it.

Patience is in order; it also allows the bank balance to recover.

There are quite a few "Fluke dividers" available on fleabay, but my KVD is seriously sexy And heavy
https://www.flickr.com/photos/anachrocomputer/24735179178/in/album-72157689996528645/

[Kosmic]

There are quite a few "Fluke dividers" available on fleabay, but my KVD is seriously sexy And heavy
https://www.flickr.com/photos/anachrocomputer/24735179178/in/album-72157689996528645/

There is one on ebay, a bit expensive though (1.5k)

https://www.ebay.com/itm/Julies-Research-Lab-Vintage-Rare-JRL-VDR-106-7-Voltage-Divided-NICE-Mod-A/302961144684?hash=item4689e4336c:g:5nwAAOSwysFb7xqD:rk:2:pf:0

[tggzzz]

There are quite a few "Fluke dividers" available on fleabay, but my KVD is seriously sexy And heavy
https://www.flickr.com/photos/anachrocomputer/24735179178/in/album-72157689996528645/

There is one on ebay, a bit expensive though (1.5k)

https://www.ebay.com/itm/Julies-Research-Lab-Vintage-Rare-JRL-VDR-106-7-Voltage-Divided-NICE-Mod-A/302961144684?hash=item4689e4336c:g:5nwAAOSwysFb7xqD:rk:2:pf:0

Oh, thanks for that. Looks like mine was a bargain!

Bookmarked, so I can see if it sells

[URI]

Once I'd got a stable reference, I ran the self tests:

Test 1 (Internal Reference) Should be: 7V +/- 0.005V is: 6.999413 PASS!!
Test 2 (A-D Internal Zero) Should be: 0V +/- 0.0002V is: -0.000280 FAIL (just)
Test 3 (AC Converter) Should be: 10V AC +/- 0.01V    is: 10.0002 SUPER PASS!!
Test 4 (Ohms Converter) Should be: 10.000R +/- 0.02K is: 10.003780K FAIL

I regard those as sanity checks, no more. After all, they are all using a reference voltage to measure things derived from that same reference voltage.

Don't forget to look at the AC voltage with shorted inputs. It should be zero, but on several of my meters it is far from that! the AC to DC converter is, of course, separate and to blame - look at the specs and there is a significant difference compared to the DC specs.

I'm currently getting 0.000236V with shorted inputs on AC. Good or bad?

Yes

That's similar to the value I saw. I've tweaked just about everything on one of my 7075s, and I especially tweaked that to be ~1uV. [..]

I just checked my different Voltmeters (ACV, shorted inputs):   
HP 3456A: . . . . 0,000286V (0,286mV)
HP 3456A: . . . . 0,000696V (0,696mV)
HP 3457A: . . . . 0,00689mV to 0,00714mV (~7µV)
HP 34401A: . . . 0,0001mV (0,1µV)
Philips PM2535: 0,00mV (despite having 6 1/2 digits on the DC V range it has only 2 1/2 digits on the ACmV range)

I was a little bit surprised by the results of two of my HP 3456As because on DCV they are much more quiet than my HP 3457A. I wonder if there's something to be done on my 3456As: I haven't done any tweaking nor calibrating on them since I have them. The difference between them tells me there can be done something on the one reading higher.   
The HP 34401 surprised me ..but then consider it's just a generation ahead the HP 3457A and two generations ahead the HP 3456A.

I think the results of your 7075 are good. If you can bring them further down -even better.   

On the other hand -sanity check: Take a look at the specs and check the accuracy of the ACV range..   

[Neomys Sapiens]

This HP kit looks nice inside.
For comparison, my latest TEA addition: https://cb.wunderkis.de/wk/AC-Source-EAC/teardown/

Still have to figure out how to operate the thing, it doesn't have any controls, everything via RS232, no description or manual nor software available. Manufacturer has still to answer my email, wonder if they'll ever do. About the same time this thing was manufactured (1990 ... 2000), I've worked for a small company, the boss would have declined support for a long time out of production unit.

Well, I know where they are sited. If they don't answer, we can molest them personally.

Okay, it's just about 160km from me

Nay, I could detour at my way to work.

[Specmaster]

@mnementh, I see you have been out flying your drone again, now this looks like fun 

[mnementh]

Solder-ily nice job mnem. 

   Granddad mode again, CJ and his mum and dad are here for the weekend. Quite a little character.

Thanks! It was actually quite therapeutic; once I got into a "process" they were "done afore I knew it".

The green ones though... well, you know what they say about the green ones.    But they are so worth the extra effort.   

Looks like CJ is again the subject of a rousing game of "Get the Baby".  Quite right!

   Here's what I woke up to on the bench this morning over my first cuppa coffee... kinda the inverse function thereof. Once the deed was done, I had to be elsewhere for a while.   

Maybe a better title would be Chaos Theory? Dinner Conversation? Politics?   

Think I'll go with Quantum Entanglement .

I quite like that actually... and it very well fits with my apprehension as I considered the task before me over my first cuppa coffee yesterday morning.

Now I have to choose between that and TEA Lo Mein as inspired by bitseeker... I believe this will be at least a two flagon move.

mnem
Zoe: You sanguine about the kind of reception we’re apt to receive on an Alliance ship, Cap’n?
Mal: Absolutely. What’s “sanguine” mean?
Zoe: “Sanguine”: Hopeful. Plus; point of interest... It also means “bloody”.
Mal: Well, that pretty much covers all the options, don’t it? ~ Firefly

   

[bd139]

@mnementh, I see you have been out flying your drone again, now this looks like fun 

My god that woman looks like my ex. And behaves like her as well.