Keithley 2001 high offset/pulsing? *fixed, pending cleaning* - Page 1
Forum section: electronics / repair

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 01:54:22 am
content: I have a Keithley 2001 meter. The symptom it has if you short it, it gets to 0, then bumps up to roughly 300uV, and falls to all zero, and so on. Roughly every 1 second or so.If you turn off auto zero, it stays at around 300uVWhat is this a symptom of? Something leaking? I replaced all the DG switches already (11 total I believe) and the electrolytic capacitorsI don't know what to call this problem.if someone knows the schematics well and can point out to me where this auto-zero thing is going on, it would help me trouble shoot nearby components. Their schematics are a big mess lol

author: Simmed
author_rank: Frequent Contributor
timestamp: May 05, 2025, 02:33:20 am
content: could be 1 of the 339/393 going bonkersleading to poor switching in the Jfet ?you probably need to check the output of the 339/393 to see which 1 is flickering ?

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 03:13:31 am
content: not familiar with what this is. LM393? LM339?I don't see them in the partts manualOh, on the AD board? 806 807?fuck this upside down probing shit. It looks like the 393 does nothing on the outputs339 out 3 looks like some kind of PWM going on

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 03:49:03 am
content: I was hoping something more conceptual to help me understand where a 300uv offset voltage can be from.It passes the DCV test. But it has 300uV offset voltage. Sounds like the test is not gonna help me. I was trying to think along the lines of "when transistor xyz is supposed to be off, it is infact leaking" so I can maybe trace down the circuit path. I replaced all the switches. I can't make heads or tails out of what its doing because of all the switches and very convoluted schematics. I power washed the PCB with flux remover under the chips (used 3/4 of a 19oz can of chemtronics) after I replaced those switches. I was hoping it would help me narrow down what part can be causing trouble.a steady 300uV offset maybe can be possible to isolate to one of the parts?I don't even care about the auto zero function right now. I just wanna track down what is making a 300uV offset. Am I missing something ?

author: Simmed
author_rank: Frequent Contributor
timestamp: May 05, 2025, 03:59:12 am
content: yea im just guessingthe repair manual did appear to have a list of things to check under 200.xthere is also 303.2 = zero reference measurewhen i see the chart, the zero are (i assume) the "off" states to some sectionsand it could be 1 of those leaking (my guess)

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 04:00:19 am
content: https://xdevs.com/doc/Keithley/2001/doc/2001-902-06.pdfThe Hi signal starts on page 2 of this document. If I got all the DG switches (11 in total), what should I be looking at next? A steady 300uV offset might be being introduced here. I believe these parts are most likely to be damaged because their close to the input.It does not show a DC failure test. But clearly to me its failing because of the gigantic offset when shorted.The first transistor connected to it is q514. But thats at the base of a FET. I don't think its leaking there ? I would imagine its something that should be off but its not. U526 was replaced and power washed so I don't think that's the problem.Then its Q516, Q512, CR533, CR534, U520 (which is connected to amps in??)IDK it seems ridiculous to me. Did anyone write a theory of operation where they go through the signal path of the meter to help me understand how it works and where it could be failing?And this upside down daughter board on headers is just pathetic IMO. I fucking hate these god damn modular circuit cards so bad. When I was new I thought they were the coolest idea ever. Now I just feel like its a god damn hack. I see what you would need to do is screw on a side board with double sided turrets on it, so you can solder a thin wire to the chip on the bottom and then clip a scope lead on top. What a chore. I guess I should build this 'adapter'.

author: Simmed
author_rank: Frequent Contributor
timestamp: May 05, 2025, 04:22:25 am
content: Quote from: coppercone2 on May 05, 2025, 04:00:19 amthe 2001-902-01C_May_2011_Repair.pdfpage 28 = block diagram (tin's block diagram on his pdf "schema_21JAN" is page 2)then later truth table 2-10 on 2011_Repair.pdfthen reference to 2001-902-06.pdf schemawell thats how i see it

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 04:23:34 am
content: I saw that one, with a bit more detail I mean.You don't get a headache looking at that 'network' they have on the schematic? I would need to spend a week in MS paint making the different sub circuits that make sense to me individually

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 04:34:05 am
content: I thought this might help me probe the daughter board with those chips you mentioned. I have the expenisve micro probe but when it has to be on the bottom its just not great (from those pogo pin probemaster guys)Idea is you clamp it to the side of the board your working on upside down, solder wires to the points you need to test, then probe the turret terminals with the scopeIt's fucking obscene, you need to resocket it every time, with a wimpy little micro probe attached, or have glue and tiny wires and ughgfhugfdujhhsdfgoujihkmp;lrefdgaijkpmon]w4r3eqtfijpkmo]seriously you might as well just replace every chip there instead of breaking it while you measure it, unless you make this or some similar insane adapter

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 04:45:13 am
content: and I am not saying the comparator is working, but I am saying that to me, if there is 300uV offset when the auzto zero is turned off, does this not mean that perhaps something in the signal conditioner is leaking and can be fixed? I thought its best to deal with the problems from front to back.Did you mean that you think something is totally flipping out and a switch is switching when its not supposed to and its like charge pumping something to 300uV?I thought this error is like 'steady state'. BUt you think the error might be from a transient phenomena that gets averaged into something steady state?? Please clarify . I do see out 3 of the lm339 is making like a PWM wave form. The other ones will have to wait because if that probe slips off the chip one more time this instrument is going to be sitting in the rain aFTER it gets thrown through a windowI was hoping you might have an idea to trouble shoot something thats not on the upside down daughter card. is there any suspects? Something where I don't need to fight gravity ? I will need to take a week to design and order parts for and and build some kind of adapter to let me probe that upside down shit without losing my marbles

author: Kleinstein
author_rank: Super Contributor
timestamp: May 05, 2025, 05:10:54 am
content: Some of the Keithley meters and well possibly also the K2001 use a bit more complex AZ cycle. So not the simple 2 steps with zero and signal reading, but also readings of the raw reference to correct for ADC gain drift. The K2001 uses 2 references: a Zener diode on the ADC board for the short time and the LM399 for the long time. It also looks like there is some digial averaging of the zero over some time to reduce noise and this may be the reason for extra low frequency noise bump at low frequencies seem with many of the Keithly meters. The 1 second period could be about the time scale where the gain / offset correction is done. A strong drift in the gain (e.g. not yet warmed up) could this cause such a ramp and reset type error.The input / amplifier paths with the K2001 are quite different for the 20 V range and 2 V / 200 mV ranges. For the AZ cycle it could also make a difference if the measurements are done with 1 PLC or 10 PLC. It may make sense to measure the symptoms a bit more (e.g. show curves) to get a few more hints one where the error may be.

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 06:28:07 am
content: Ok that sounds complicated.Maybe its a good idea to turn off the auto zero and track down the 500uV offset (after its been running a while it drifted while I was working on it), starts at 300uV.I am thinking working in 'steady state' is the best idea here. I just bought a bunch of micro grabber cables and shit so I can probe things nicer ($250 of adapter, grabber, etc).Do you have a plan for me to try to follow to just find it with auto zero turned off. It should be alot lower then hundreds of uV. When I just turned it on now its 430uV and its drifting up to 460 in like 20 seconds5 minutes later and its 506uV offset.7 min its 520If I turn on AZ again, without turning off the meter, then turn it off right after, the offset drops to 330uV, and it begins its rise. So it like resets it to some baseline.Can this tell me where the problem might be? If you drain it and then it goes back up it sounds like a 'bleed' problem. I feel like some shit like a capacitor is being charged up, then the auto zero drains it down to 0 (as shown on display, or close to 0.000mV), then it immediately charges up again to ~300uV when the AZ is disabled, then bleeds up.So the fault seems like something akin to a 300uV source (fairly low impedance) and then a bias current (restricted source) that bleeds it up.Like whatever is causing the problem can be described as:1) a voltage or current source that bottoms out at around 300uV. It instantly recharges the thing after the AZ zero's, and it can be manually triggered by turning the auto zero on and off to reset the display2) Another source that goes to a higher voltage but its current limited, which makes it slowly raise the voltage on top of the 300uV , charging whatever capacitance is holding the level (which gets it from 200 to 500 in 5 minutes, then 500 to 520 2 minutes later). To me it seems like it slows down after it gets to some where like 500uV.I know its probobly one thing, but that's what the math looks like to me if you describe the problem in sources. Like the final source would have a fairly low impedance @ 300uV and then a much higher impedance at ~500uV. I suppose I should leave it on for a while to see what it's maximum voltage is where it stops growing. I will leave the meter on for an hour and see how high the offset will get under short circuit input condition with AZ turned off.Can anyone conceive of a possible fault that causes this behavior? I don't have much experience with high Z electronics. tHEY MAKE ME MAD. I like my op amps running hot, with a 50 ohm input impedance.

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 07:29:41 am
content: from the last post I turned AZ on and off and its at 495uV (1 hour)SO it maxes offset at around 500uV within a 1 hour time frame (starting at around 300)

author: Kleinstein
author_rank: Super Contributor
timestamp: May 05, 2025, 08:49:52 am
content: The K2001 has no analog auto zero, so no capacitor that stores the offset voltage. The AZ part (especially the part one can turn on an off) is the digital part. In the simple case the AZ mode alternates between a zero reading (with the input switched to 0) and the actual input reading. The result is than the digital difference.With the Keithley meters they are likely doing some odd averaging on the zero readings, but this should not make a huge difference.For the non AZ mode it is normal to have quite some drift from both the input amplifier and the ADC itself. It can take something like 1 hours to stabilize from the turn on.Normally the non AZ mode should start with the last AZ mode zero reading. So after switching from AZ to non AZ mode one should be in the 1 µV range for the offset and than maybe over a few seconds mayby dift a few more µV. So the change from 430 µV to 520 µV may be normal for still in the warm up phase.A first point would be to record some data (e.g. store at the PC) for some time for different ranges, especially 20 V and 200 mV for both the AZ and non AZ case. The 20 V range uses a different input amplifier and would be more sensitive to ADC effects. The 200 mV range would be more sensitive to amplifier effects and less to ADC effects as there is additiona gain in front. So I would expect a very different effect depending on the range used.AFAIK the 20 V range uses no AZ switching for the input buffer (U341) and kind of AZ only for the ADC. The lower ranges use AZ switching also for the input buffer (Q330+U335). The amps part would be without the input buffer - so looking at the offset / zero for amps could also be interesting.

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 09:33:40 am
content: But if its pure digital, why does it reset it to 300uV when the auto zero is turned on and off???It drifts to 500, then if you turn auto zero on and off it will start to drift up from 300uV again, and eventually drift to 500uV. (meter is powered the whole time)That makes no sense to me. Why does it slowly drift up each time to 500 and stop when you turn AZ on and off.There has to be a better way of trouble shooting then taking recordings. Holy shit thats whack. There is 300uV right off the bat. THere has to be something detectable with probing that causes this problem??Like things that come to mind in the signal path-busted op amp offset voltage.-leaking transistor that is supposed to be off-something with a diode

author: Kleinstein
author_rank: Super Contributor
timestamp: May 05, 2025, 10:07:20 am
content: Staring with 300 µV offset is indeed odd. It may need a special call to zero out the non AZ mode.A point to check could be the input current - excessive input current could cause additional offset error and drift from the resistance in the protection.What range is used for the measurements ? If Auto scale, it should be the 200 mV range. Other ranges can be different, especially the 20 V range.

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 10:09:23 am
content: its the 200mV range.I wish these MOFO would tell you WTF you are supposed to probe on the circuit in different points if you say hook it up to a 10mV source so you can find abnormalities. Thats how you find problems in most things with a test signal to find where the deviation is. Or what it should be if the input is physically shorted. That's what you do with literarly every other equipment. Scope, amplifier, signal gen, etc. I feel like that is what normal trouble shooting is. I don't know what this is.Hook up 10mV power supply or short the thing1) measure TP at end of block 12) measure tp at end of block 23) measure tp at end of block 34) measure tp at end of block 45) measure tp at adc input

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 10:28:08 am
content: How do you measure current if the input is shorted? Like short it with a ammeter instead?Or do I need to use a source of some kind?Something with a electrometer?

author: Kleinstein
author_rank: Super Contributor
timestamp: May 05, 2025, 11:24:20 am
content: There are some trouble shooting instructions in the service manual. For the very early instruments the troubleshooting instructions where very detailed. However with more modern, more robust, but also more complex instruments the instructions only cover some more common defects and can't cover all. The described error looks like an odd one that is likely not covered in the normal procedure.For a zero reading in the amps range, just leave the input open. Internally the amps more is very similar to the 200 mV range, but without the extra input buffer. So the comparison would check the input buffer part and related switching.To measure the input current one can still use the meter itself. One way is to connect a 10 M or similar resistor to the input and compare the reading to a short. Another, more sensitive way is to use a low leakage capacitor of some 1 nF to 10 nF at the input and look at the rate of dift. With 1 nF at the input 1 pA of input current would result in 1 mV per second of drift - so easy to measure. No need for an accurate resistor or capacitors. It is about the rough size of the current (e.g. pA or nA range), not some 10% detail.

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 06:04:52 pm
content: I think its a bit more sinister then that, when I worked they did not actually want these types of instructions made for a product even if I was willing and had the time (i.e. side projects when waiting on stuff). Now its considered 'too revealing', I guess to lazy counterfeiters. I just thought that it might keep some stupid things out of the barely profitable overloaded (backlog for a year+) repair department and make the product desirable for smaller customers with small pockets (big ones are lazy anyway and won't change the mains switch even if they have a a spare infront of them. They might be supposed to save money but its only if someone is actively pressing them lol. Like anyone is gonna fight a lab owner for sending some test equipment / tools for repair. Its like trying to give a parking ticket to someone with foreign immunity).And they wanted email questions so they can try to do target advertising.And I did the current test protocol. The 200uA rangeismalfunctioning in the test, but not the volt range. So it picks up the fault on the 200uA test but the 200mV test passes.I can try a 10 meg resistor. My electrometer appears to be malfunctioning (keithely 616), I turned it on, let it warm up, zeroed it on volts, then after a while it got a 400 count offset and the full range adjust only gets it down to 200 counts. I guess that needs a repair, or replacement. A long time ago I put deoxit on the range switches when I knew I was not gonna use it for long while, I wonder if it go on those resistors in glass. And it needs the triax replaced. Glad I don't need it right now. Because I did notice when i hook up a 34401A in 10Gohm to the K2001, there is some offset I can measure that is pretty big, I think 60mV for measuring the input.. something to do with bias current I think. I had some op amps before I could not adjust without the K616 because the 34401A was throwing it full scale.. then when I hooked up the K616 analog out to the scope, it finally made it possible to see whats happening. I really should try to clean it and see if it works or buy another one. That meter is annoying because it had mad crusty contacts on the switches but it also needs to be very clean.I put deoxit on my fx9750 amd processor too (gold) and graphics card and everything else in the PC too last year, at least thats all working fine lol. i bet people would kill melol the 616 has a physics package in there.I thought it was a magnetron for a second. i think this electrometer might have to go back on the shelf until i die. someone would need to be highly motivated to go in here. looks like that person was in 1978.that was stupid and demoralizing to look inside the 616. I really am too attached to it for its value. The haunted house on my property. Oh hell maybe I will take it apart, measure the raisl, carefully, maybe spray it down with IPA anhydrous from MG chemicals and see if it works. im so curious to see what happens if you try to connect the K616 in volts to the K2001. Will it give offset like 34401A @ 10Gohm? I think it won't.what the hell did i get myself in to. i could have thrown this thing out, and bought a new videocard instead. Seriously I think this thing gives me panic attacks the same thing happened last time, it needs to be that monster range switch, mount fucking everestlmfao this is like some out of shape fool buying climbing equipment to climb everset. thats how i feel after visiting probe master and digikey last night. Theoretically I have the technology do this. LOLL

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 08:19:48 pm
content: So I plugged in a 9.9 megaohm caddock into the front. The uA scale is also jumping from 0 to 200nA periodicallyoffset started at 60nA and its climbing with AZ turned off.With the 10 meg resistor plugged into the front amps jack, there is no difference on the display if you turn on rear input or front input (disconnect it);. So the resistor looks like it does nothingIf you put the resistor into the DCV, with AZ disabled, you get a offset. It looks like a noiser offset then if its shorted. With resistor being measured in DCV, the offset right now is -500uV, fluttering between 500 and 400 (noisy). If I connect ashort across it, it stabilizies to 460uV with only slow drift on the last digit2w ohms says 9.884, noise at 4I soldered a caddock to a dual banana solder post thing and put it into front panel

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 08:42:24 pm
content: QuoteActually OK I see a behaviorWhatever offset it gives you with AZ disabled and caddock installed, if you short it out with a jumper wire, the ACI reading changes by about 5nA.So there is a offset difference of 5nA between somerthing like 0 ohms (1 foot jumper banana put into rear of dual terminal caddock load) and 10,000,000 ohms.This is the number you were thinking about me getting? I need to make a short banana standard for this with a thick piece of copper and 2 bananas in a U shape soldered together good, I broke my other solder dual banana and the terminal spins nowSo the difference between 0 ohms and 10M ohms is ~5nA.That is alot no? Not sure exactly but I though these things are supposed to be in pico amp range?How should I do the capacitor? I think my dual banana jacks are pomona, so it should be the good plastic. I thought to solder a 10nF foil capacitor to a dual banana jack, short it in the DMM, then let it charge for say 30 seconds, then take it out and put it into another meter?

author: Kleinstein
author_rank: Super Contributor
timestamp: May 05, 2025, 09:24:17 pm
content: This got quite confusing and mixed up. So not sure I understand all of it.It is normal that the input reading is more noisy with only the 10 M resistor at the input. There can be hum pick up and the amplifier will have some current noise and current spikes from AZ switching. At the very least the 10 M resistor has quite some Johnson noise. The test with the external 10 M resistor would be with the DMM in voltage mode and the K2001 would read the voltage. So no 2nd meter needed. The external resistor is a way to replace the external electrometer.The current should be less than some 50 pA and quite often would be more on the 10 pA range. So 10 pA time 10 M would give an additional offset of some 100 µV. An observed difference of some 50 µV corresponds to some 5 pA whicht is pefectly fine. So there seem to be no excessive input current.Looking at the current ranges is a different test from looking at the input current. The current ranges are relevant with an open input and thus naturally zero current. A short at the inputs should not make a big difference, though there could be some thermal EMF. the 200 µA range would have a 1 kohm shunt. So 60 nA would correspond to 60 µV of offset.Getting a comparable perioding signal as in the voltage range points to a problem that is not at the very front end, but more with the ADC or main amplifier. So the input buffer and AZ switching there is likely not the problem.How much drift is there in the non AZ mode and current range ? this should be the drift of the LT1007 main amplifier and 1/50 the ADC drift. So ideally there should not be very mich drift also in the non AZ mode. Normally much of the drift in the 200 mV non AZ case should be from the input buffer (Q300) and this part would be missing the current range. Especially the LT1007 should not drift much (a few µV maybe).If there is significant drift from the amplifier it would be visible at the signal to the ADC (AD_in) or output of U322.I don't expect much from this, but how is the 2 V range with a short behaving ? If the problem comes from the ADC it show a 10 x larger error than the 200 mV range.

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 09:24:53 pm
content: oK i PUT A 6.8nF capacitor on another new pomona dual banana jack I bought a few months ago (red color)from digikeyI have mr. k2 in DCV with AZ off, offset reading ~300uV. When I plug in the capacitor, the display voltage instantly rises to 16mV. After 2 minutes its at 84mV. If I try to take it out of K2 and put in HP34401A (set to 10gohm) it reads something like 62mV and droops slowly. If I short it out with the new shorting jumper I made it drops to 0V, and then when I remove the jumper there is some low residual reading.A dmm charging a cap to mV's quick sounds like bad

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 09:30:16 pm
content: 2V range shows short circuit error of 00.000460V200mV range shows error of 000.3987mVor 0.0003987V (200mv) vs 0.000460V (2V)so the difference is ~0.00006V between 200mV and 2VIf you divide them the error is 15%

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 09:35:55 pm
content: And I did it again after having the meter off for a short period,200mV error = 300uV2V error = 150uVSo this time it 50%. If you let it sit the error decreases (they converge when i swap between the ranges every few seconds). It does not have good match right at power up, compared to the 15% when it was on for a whileBut its not looking anywhere close to 1000% like your theoryill try to do some more formal expereimnts with a stop watch later i did too much running around today i should get away from this for now, its starting to give me migraine

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 10:14:44 pm
content: I re read what you wrote a few times after turning down the AC and trying to enjoy a movieQuoteI can't do this measurement even with AZ disabled..The reading with a 10 megaohm caddock soldered to a solder post style double banana jack is 000.5xyz, where xyz = unstable jitter. X is between 5 and 6. If I put a short over the resistor (another dual banana jack, this time with a 14 awg copper wire soldered across the turrets), it goes to 000.543x, where the x is fluttering.

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 10:36:15 pm
content: And for the capacitor experiment, this is what I see.1) put capacitor into DCV jacks with meter set to DCV2) put short circuit over capacitor to make sure its all zeroed - (000.321)3) remove short circuit over capacitor4) watch voltage spike to-8mVinstantly as the short is pulled out5) watch capacitor driftShould I ignore this initial instantaneous jump to some mili volts of charge, and then just measure the change in voltage over some time period? Why does it jump ? To me thats like rapid charging. Is this because I am using a dead short and its making the meter do something funky when its removed? Perhaps I should short with a low value resistor? (1K)?

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 10:55:42 pm
content: I put in the cap (6.8nF), inserted the short, and started a stopwatch right as I pulled it out1) with short inserted: 000.3192 mV2) after removing short and starting stopwatch: +13.45mV (I don't understand this jump)3) 2 minute 5 seconds mark : +5.04mV3) Hit stop button on meter and stopwatch 13m25s : -41.5mVso 55mV charge in 805 seconds on 6.8nF, or 68uV per secondAm I right in this being 0.464pA???I used this:Current = 0.0000000068*(0.055/805)AMPS = FARADS*(VOLTS/SECONDS)That's 464 femto ampers leaking ??

author: coppercone2
author_rank: Super Contributor
timestamp: May 05, 2025, 11:45:19 pm
content: I did this experiment to try to understand if the results are changing because of the "jump" that you get upon disconnecting the short circuit, which makes it start in some number of mili volts. I see that if you sequentially short it with a short circuit and 10 meg, its possibly to get it to start near 000.x mV (lower offset on starting). But its touchy, I tried a switch and it made it worse... the best is that you need to gently 'tap' the capacitor with the 10 mega ohm resistor to drain it before the experiment. I don't know why. It strikes me as bizarre. If you try to peck it with the short, it always settles at some number of mili volts offset.Start of experiment: DC V, AZ turned OFF,Inserted:1) double banana jack capacitor 6.8nF2) double banana jack caddock 10MOHM3) double banana jack short circuita) Voltage reads 000.324mVb) after short is removed, voltage reads 000.335mVc) 10 meg is removed, start of experiment : 000.500mV (I had to "prod" it with the 10 megaohm resistor about 4 times to get it to 'start' at less them 1mV)d) after 5 minutes 23 seconds : 32.5mV32mV over 323 seconds, which is 99uV / second. Its shorter duration then the last one, so the ballpark is similar. I guess whatever is causing this offset voltage, its not having an effect on the rate of leakage.But do tell me if you know , why does it randomly settle to some mV value as you remove the short circuit while a capacitor is connected??? Am I some how literarly jamming or pulling electrons out of there? (triboelectric?) Why does using a toggle switch make it worse then pulling the banana short out with my hands? Would a low current (dry contact) expensive switch help ? It makes me feel like I am dealing with dough or something.. its sticky and I am pulling dough off a scale... something weird like this. It's kind ofinfuriating. The experiment should start at 0, not a random offset of some kind. UghI feel like a doofus when im 'prodding' the meter input jacks with a 10 megaohm resistor to get it to start the experiment. This cannot be the way things are done??? I am guessing this means my hardware is bootleg, like it needs to be gold plated double banana jack made out of sapphire or something? Or am I charging it with a thermocouple?But anyway, since it looks to be less or about 1 pico - amper of leakage.... this rules some fault out at least?Granted I don't think it says anything about where the 330uV is from, but at least you can tell that the leakage current is low in front of the circuit before the first isolation area (amplifier)?

author: coppercone2
author_rank: Super Contributor
timestamp: May 06, 2025, 12:48:20 am
content: I also found my old SOIC 14, Soic 16, SOIC 8, DIP 8, Dip 16 and dip 18 clips to help measure that PCB. I spent a while cleaning them by scrubbing with alcohol, now I will go wash them in the ultrasonic and give them a careful treatment of deoxit (not drenched) so I can safely probe the various chips on this board. Hopefully along with the various micro grabbers and osciloscope probe to micrograbber adapter I made up (SCOPE PROBE TO BNC (insert collet), BNC TO BANANA, BANANA TO 0.025 SQUARE TO MICROGRABER) and pogo pin scope and multimeter probes I can probe around on the PCB without destroying anything and also get reliable measurements.

author: Zucca
author_rank: Unknown
timestamp: May 06, 2025, 02:25:22 am
content: Have you recapped it?Also, I propose replace shift registers 14094 and all analog switches (DG411/DG404/DG211). It is much faster than troubleshooting these failures.The aboves are weak points of any K2001

author: coppercone2
author_rank: Super Contributor
timestamp: May 06, 2025, 03:18:05 am
content: Yes to caps, yes to DG switches. Now you are saying to hit the shift registers?Anything else you think is weak... because washing this thing is a bigger problem then changing parts. Especially if its some cheap crapIt does make me think of something with digital parts because it messes up on auto zero. Like something is undefined or messed up and two switches are being opened at the same time that should not be, or one switch, etc. The shift registers lead to incorrect commands being issued to the analog switches I take it? Then you have something like messed up traffic lights in a city causing crashes? Like they are the parts controlling the DG switches? (acting as serial to parallel converter kind of for the MCU?)***irrelevant**Also decided to scrap my 616. The resistros are nice. I will keep them for playing. It looks totally shot on the front end. A few times I wanted to buy a newer one anyway, this one is like occupying space I need. I noticed these MOFO use PALNUTS in the chassis, the evil sheet metal nut I hate. I got it for $30 years ago IIRC. I am very excited about actually buying a moderner EM and have zero guilt for possibly having destroyed it some how. A professor long ago told me during the coarse of a real project, they managed to destroy SIX electrometers (for reasons unknown) while studying something. And this dude was one of the smarter ones there when it came to T&M. I want the standoffs too. I have those low bias super op amps to play with if I save these parts.Did anyone else feel on edge after trouble shooting the K2001? I don't know what it is, but something about all these really small measurements that take a long time gets into my head. I don't think its relaxing. Thinking about the circuits in it made me feel kind of strange. I think its the high-z stuff. And now I have more teflon standoffs then I know what to do with, from the K616 (RIP). With these resistors and mounting hw I got maybe I can revisit those diode dark current and things LMPsomething circuits I was playing with eons ago

author: Kleinstein
author_rank: Super Contributor
timestamp: May 06, 2025, 07:51:38 am
content: The test with the capacitor showed very little drift rate and thus very low current. The jump from removing the short could be some charge transfer from the hands. Kind of charge injection of the mechanical switching. The test with the 10 M resistor also showed that there is litte input current, though a tiny bit more. So I think the input buffer part is OK.For the test with the 2 V range the offset is comparable. There can be some cal constants and when setting the zero in the non AZ mode. So the absolute value of the offset is not that relevant. The question is more if one sees a comparable ramp and reset typ variation. To compare this it would really help to get a way to record data and show them as a plot. In the long run one would very likely want to use such a higher resolution meter in combination with a computer anyway. The final tests for noise and drift would also need recording data.With the offset issue also happening in the DC current range(s), there is not that much circuitry before the ADC. So this issue could be at the ADC - like some issue with the integrator reset or a linearity problem. A linerarity problem would also need data recording for diagnosis.A problem with the shift registers is not that likely and would normally cause a big error and errors in the self test. There is rarely a partial fail with digital logic.

author: coppercone2
author_rank: Super Contributor
timestamp: May 06, 2025, 08:42:10 pm
content: Hmm it still seems to be worth a shot, its six dollars of parts and maybe $10 of flux remover fluid. If I replace the ADC that is going to basically totally screw all the calibrations right? Like completelyI did not go deep into the test, but there is also some problem with AC amps switch and Amps protection. I thought that dealing with the issue that is present on DC might fix that though. AC amps is way out thereDealing with the problem of DC jumping around seems the most prudent, and whatever that is, DC test does not say anything badIf you can't get it to measure DC then I feel that everything else is not relevant

author: Kleinstein
author_rank: Super Contributor
timestamp: May 06, 2025, 09:17:46 pm
content: Swapping the ADC may not change the calibration that much. AFAIK the K2001 has a LM399 ref. on the main, that should be used for the longer time reference. So the ADC gain and zener ref. on the ADC board are corrected from time to time (I still don't know the details - this could set the 1 second range period for the odd ramps).The DC part is indeed the first part to get right. AC it than one more step on top.The amps protection, if not working could mess with the 200 µA range, would be likely less on 200 mA / 2 A.So starting with the DC part is a good idea. Of cause the very first point is to check the supplies and the somewhat odd AC regulation (e.g. check if the unregulated DC is reasonable stable and voltage).

author: coppercone2
author_rank: Super Contributor
timestamp: May 06, 2025, 09:24:42 pm
content: OK, Actually, do you know WTF +8VF and -8VF is?Because their not 8V or -8V and not stable. But I thought VF might mean something other then voltage.Or it might be BUF not 8VF, I can't tell if its B or 8. But the V looks like the V, not a U

author: coppercone2
author_rank: Super Contributor
timestamp: May 06, 2025, 09:28:05 pm
content: And what about the pins on the ADC cardwhat are1) ADTRIG2) COM (master common for all measurements?)3) S COM (signal common? what for?)4) -VREF5) DC STB6) STAT17) D GND (for 5V?)Are any pins there worth measuring? There is alot of pins. Some sound digital. Also there is AD_INI will just write them al;l+5VDGNDD_OUT (SPI?)SCLKR1_STBR2_STBFREQDAT_OUTDAT_INSDXSTBAD_DATDC_STBADTRIGOHMCB600HZCLKSTAT1-12V+12VCOMAD INS COM-VREFIf you jam a wire in the hole near the header it gets stuck into some kind of connector so you have a probe pointI always love if they write STAB on something (like YIG). I do infact usually want to stab it.... almost wanna keep a ice pick to perform STAB related maintenance. But this just says STBhttps://www.pristineauction.com/a3293894-Henry-Hill-Signed-Ice-Pick-Inscribed-Goodfellas-JSA-COA

author: Kleinstein
author_rank: Super Contributor
timestamp: May 06, 2025, 09:52:32 pm
content: +8VF and -8VF are +-8 V relative to the BSCOM signal. They are not super stable, but just stabilized with zener diodes and emitter follower.The AD_in signal is the input to the ADC.-Vref at the ADC is a negative ref. voltage from ADC. So an output from the ADC module, derived from the low noise zener there.

author: coppercone2
author_rank: Super Contributor
timestamp: May 06, 2025, 09:54:48 pm
content: What is the BSCOM? I only have SCOMDo you know what -VREF should be?

author: coppercone2
author_rank: Super Contributor
timestamp: May 07, 2025, 04:42:10 am
content: IF i measure fromSCOM to the VF8s I get7.09 and -7.51they are drifting alotRef- is -10.3212/-12 = 14.88 and -15.16 (I think its mislabeled?? they agree with the +-15V5v = 4.98If I short it out, AD In is 229mV, display is 000.597DC stb is 670uV (and display is 608uV)I also had a thought: Is the same signal chain controlling the DC zero test and the normal operation, or is there an altenrative path (like a... OR logic gate). So perhaps for the zero test, there is a OR-gate logic circuit that is making the thing turn the zero on properly, and pass the test. But then, during normal operation, that circuit element that is triggered by the OR gate is not triggered because one of the inputs of the OR gate is damaged. ? I know you said its digital zero, but maybe there is still some digital parts involved outside of the ADC ? Like if the ADC has a "ZERO" input trigger pin. Then that pin is connected by a OR gate which can trigger the ADC Zero from either the TEST MODE or the OPERATION MODE?? Its the only way I can think for it to pass a self zero test but not zero properly during operation? And like I don't necessarily mean a 74 series OR gate, just something that ends up behaving in this way that there is two switches to trigger one thing and one of the switches is broken. Can those shift registers do something like this if their messed up? I don't know how its wired.I mean, should this fault not make basically every test the machine has fail???

author: coppercone2
author_rank: Super Contributor
timestamp: May 07, 2025, 04:51:33 am
content: I think this is going in circles after I did the ppm error and spec, but it looked suspicious at first********I did notice something. On the penultimate range the display is jumping to mV offset when the AZ is enabled and DC input is short circuit (I am writing down the peak)200mV - 200uV2V - 200uV20 - ~500-600uV's200V - 12mV's1000V -in the 18mV'scould this be another indicator that helps localize the problem??Why does the magnitude of the AZ jump increase so much with the 200 and 1000V range. That is 6000% and like 9000% error abnormality.With AZ disabled its (taken fast)435 uv 200mv680uv 2v6mV 20v65mv 200v300mV 1ksteady state offset erroryou said something about different calibrations and drifts for the ranges but isent that like gigantic error?I got lost in the conversation before... can you refresh me on why this is? The only thing I also notice is that 0.3V of 1000 is or 0.03% error. I guess thats pretty small. The spec is 30ppm and that is 300ppm but its not warmed up and not auto zero. OK so I guess that might actually be fine in that context.

author: coppercone2
author_rank: Super Contributor
timestamp: May 07, 2025, 06:47:01 am
content: 1) short out meter2) measure AD IN with AZ enabled3) measure AD IN with AZ disabled#2 = jumps along with meter display. I am using 5.5 digit slow, and if I put it in the manual range, it will actually over-load the 34401A measuring display#3 = steady offset . Its scaled from the value on the K2001 panel, but its steady and drifts similar. No bumping.On a properly functioning meter, this measurement would still look like this?When you meant that its digital, you just meant that its not using a DAC to invert the voltage and cancel it out before the ADC input right? So the ADC is supposed to record this. So its almost like.. the ADC is not keeping some value in memory?SO like... what... its skipping a instruction cycle on what to do internally??? So like.. the ADC is not recording the value i and subtracting 0 from the display after the AZ cycle??? WTF how is that possible like currupt memory?I am hoping there is some control signal to the ADC making it not do something its supposed to do missing? Otherwise im SOL?

author: Kleinstein
author_rank: Super Contributor
timestamp: May 07, 2025, 07:09:20 am
content: The +-12 V supplies are likely mislabels, maybe from a different instrument that may want to use the same ADC modulte. The schematics from the service manual show +-15 V supply at the ADC module. It may still work with +-12 V though. So I think that part is OK.The BSCOM signal is no going to the ADC module, but on the main PCB. It is a buffer amplifier following the main input. The +-8VF are a kind of bootstrapped supply for the input buffer (and some switches) that follows the input. It is not super stable and may drift by some 5 mV/K from thermal effects and of cause can be all over the place with an open input.The observed offset error can be quite a bit larger in the 200 / 1000 V ranges, as these go through the 1:100 divider first. So the input signal is divided and the result from the ADC is than digitally muliplied by the factor 100. The 200 V range corresponds to 100 x the 2 V range. So 680 µV in the 2 V range are expected to give 68 mV in the 200 mV range. Given the drift an scattering these offsets are consistant.The less consistant part is between the 200 mV and 2 V range. They have different gain at the main amplifier and this would suggest an offset after the main amplifier. The 20 V range on the other side has a higher offset and this would suggest more an offset at the main amplifier.The offset in the non AZ mode is not that much to worry about - there is a kind of AZ cycle that is / can be called once and there are likely offsets that are subtracted digitally anyway. The worrying part is having so much offset in the AZ mode.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 07, 2025, 07:42:43 am
content: Quote from: coppercone2 on May 07, 2025, 06:47:01 amThe non AZ mode should show the steady signal, and this is OK. There can be some additional offset (maybe a few 100 µV) from the main amplifier. So the description looks normal.The AZ mode is more complex and one may have to look at the signal more with a scope or digitizer (e.g. DMM at 10 V, 1 PLC non AZ or faster and record to PC with the K2001 in 10 PLC or slower). There should be 3 different signals in the sequence:1) a zero reading (the input amplifier set to zero)2) the input reading3) a reference reading going throug the amplifier.So the 34401 in normal mode could well be confused, jumping between ranges and getting overload at times.I don't know the exact sequence that is used - it can be a bit complex (like 9 cycles with zero and signal and than 1 cycle with ref. and input) and depend on the PLC setting. The speed specs suggest that there is not just a simple 3 or 4 step cycle with signal, zero (maybe an extra ref. zero) and reference like the in the K19x meters.For the 200 mV and 2 V range the zero signal for the AZ cycle is coming from U323 and Q527. For the 20 V range I don't know exactly how. For the 200 µA range the zero signal should be via U319 / R340 and thus a different path. As the 200 mV and 200 µA range are somewhat consistant, I don't think this part of the switching would be the issue.The offset correction in the AZ mode and when initializing the zero for non AZ mode is digital in software, well possibly on the digitial board. So no DAC to subtract an offest. Some other DMMs, like the HP3456 or ADTV 6581 have also some kind of analog offset correct at the ADC. The K2001 does not have this and in this respect is simpler. It is rare that a CPU would fail at a few points. It may fail to store the zero for the non AZ mode (may end up in EEPROM with cal constants), but the zero for the AZ mode should stay in the RAM only.It don't think there is something really wrong with the CPU / memory. It is more like getting a bad zero reading or maybe large errors in the ADC. Maybe things like a poor ground contact or supply hum.Just a strange thought: what the history behind the meter - are the boards swapped and maybe version conflicts (up to the point of having a K2002 digital PCB, that is very similar) ?

author: coppercone2
author_rank: Super Contributor
timestamp: May 07, 2025, 08:49:34 pm
content: Alright I had to cobble together a better ground lead for my scope then the alligator clip, every probe has its own ground and managed to put something together that accepts a tek grabber so I can try to look at it with scopeThe ADC in is complicated. I don't have fancy deep memory tech to look at thisThis is with input shorted AZ on.On a slow scroll rate, it looks like pulse train with 3 levels. High, lower, high.... once every secondIf you zoom in the shortest pulse looks like 10uS or so, then maybe a 20-30uS, 6mS, 20mS.. those short spikes look like they happen between the longer pulses.I would say like.. damn thats pretty god damn dirty. The voltage levels are 9,7 and 10VThis is at the AD IN pin with oscope ground on the S COM pin.Why are the voltage levels of all these pulses so high? I mean I can't figure out what its doing. I thought it be a tiny little square with wave 0, not high voltage pulse trains.It looks kinda like this (probe fixed @ 10X, scope set to 10X with 5V/Div), looks like it occurs every second or so.I gotta say, if this is how these meters are supposed to work, thats kind of insane.the 'buildings' are 700 miliseconds long in total (all three),the first one is 8 pulses, then a fatter pulse with a drop off to a lower voltage (from 9V to 7V) before it goes to zero,the middle one is 8 pulses @ 7V, the last one is also 8 pulses @~10V. Each of the individual pulses is something in the 8-10ms range, with a few ones being wider.I can try to take pictures and like get more focused measurements if it is useful

author: coppercone2
author_rank: Super Contributor
timestamp: May 07, 2025, 09:09:12 pm
content: how the hell is this thing supposed to work if there is that much shit in the ADC input... nearly constantly? This is beyond my capacity to understand WTF its doing. And the signals look nice. The scope probe is pressed into the hole near the AD IN pin (no grabber), and the ground lead is clipped to the header pin that connects S COM using a tek grabber that looks like a hyper sonic+ jethttps://www.w5swl.com/products/tek-tektronix-smg50-smt-klipchip-adapter-206-0364-01-mini-grabber-for-smds-etcDo those buildings correspond somehow toQuoteHow does 9, 7, 10 v make sense? That is full scale I bet, the rail is 15V. And why is it pulses. What is it doing that needs 24 pulses? And what is the 10uS pulses?I thought it would be like one little pulse every second, not constant pulses for almost a secondHas anyone written about what this meter is doing? I would have thought its a short from a digital rail, but all of it goes away when you turn off AZ.

author: coppercone2
author_rank: Super Contributor
timestamp: May 07, 2025, 09:54:45 pm
content: and the digital PCB does say K2001 and the analog board says that too, and also the ADC board

author: coppercone2
author_rank: Super Contributor
timestamp: May 08, 2025, 06:11:56 am
content: I redid the measurement, more precisely the calibration signal is 700ms long for the' buildings '(not 800), and the voltage levels are correct. I could not figure it out so I checked the type of probe and the settings on the scope, and made sure the scope is working by probing the various voltage rails. I was really sure I made a mistake with the probe ranging... but it looks correct.I.e. I probe the 15V rail, measure 15V on scope, then probe the AD IN without changing settings. It really is like 9V. IDK what that has to do with zeroing anything??And this probe does not have the range switch on it, its fixed 10x. I know you could get into trouble with the range switch on a probe.If you think there is anything here, I can also probe the input with the short coil spring scope ground connector (no wire, spring mounted to front. )

author: Kleinstein
author_rank: Super Contributor
timestamp: May 08, 2025, 07:29:24 am
content: One has to be careful with connecting more than 1 ground to the scope. The grounds at the scope are usually connected. So one would also connect the ground points at the circuit.The AD_in signal looks indeed odd. The short µs range pulse are likely transients from switching between signal paths. Ideally these would be smaller, but they could be normal.Having a higher voltage towards the ADC can be normal. For the 2 V range the meter produces an internal 1.75V range reference signal (via a PWM divider) that with a gain of 5 would give some 9 V. No sure how this is done in the 200 mV and 20 V ranges, but they have to measure an internal reference from time to time, as the ADC uses the low noise zener and not the LM399 reference. So they have to do that extra link from time to time.Likely the PWM could also produce a 200 mV range signal for that purpose, or they use the 2 V range and to the reference measurement this way.What is surprising and likely not normal is to have 3 different levels. It should be a fixed voltage all the time. The sequence is also a bit odd. With a 50 Hz, 10 PLC setting the expected sequence would be something like 200 ms the input signal, 200 ms the internal zero with maybe some short (10 µs or less) spikes in between. This part is expected to repeat most of the time. From time to time (like once a second, but could be more frequent, up to every 2nd cycle) one may have a different sequence, like 200 ms the signal and 200 ms the near full scale reference signal, maybe with a 3rd step of zero - that part is what I don't know. With 60 Hz mains the times would be a little faster, like 166 ms each.Even with a 1 PLC mode the pulses should be at least 1 power line cycle, not 8-10 ms. There would be an odd chance that the meter is getting a wrong mains frequency and tries 120 Hz for mains ?For testing it may help to have a non zero input signal, so that one could see, which phase is the input.Is the reading rate about the expected speed. Too short pulses would suggest faster than expected readings.With so much going wrong, I am surprized to not see a long list of errors in the build in self test. So please give the complete list of errors, including those for AC and current. They could still give a hint on what works and what not.

author: coppercone2
author_rank: Super Contributor
timestamp: May 08, 2025, 07:58:59 am
content: Errors are309.1309.2309.5309.6310.1412.1

author: coppercone2
author_rank: Super Contributor
timestamp: May 08, 2025, 08:02:16 am
content: So everything but one range in amps (I don't think you can fail 309.4? or maybe you can, well it passes this one and 309.3 (20mA) )and then it also fails:then the amps protection3.10and ac amps control switch4.12If I try the self test with a short it starts complaining about ohms. I say this because I wonder if you can determine some problem by intentionally causing fails and seeing which self tests fail with different load attached.Maybe that can also tell you something if it can pass 309.4 but fails .5 and .6 . It sounds like its related and may isolate a problem. If its not all baloney

author: coppercone2
author_rank: Super Contributor
timestamp: May 08, 2025, 08:08:23 am
content: Hmm and I wonder.... if one of the voltages of the pulse train segments in the oscillograph is true, or if all of them are false.If I knew what its supposed to be, then maybe it could tell me if one of the tests is correct, and isolate problem to the two incorrect portions. Perhaps the highest one is correct (last one), and the other two are getting loaded by some malfunctioning component which attenuates them? Or if the lowest one is true, perhaps there is a amplifier over amplifying

author: coppercone2
author_rank: Super Contributor
timestamp: May 08, 2025, 08:56:41 pm
content: I do have a floatable HP8904A here, which can put out low DC voltages right here set up, so I can hook that up to the meter to bias it, and I also have a supply amp I can hook up to get stable currents from that if I put in a constant current resistor, which I also have (4-wire 10 watt guys from 0.1 to 10 ohm iirc), the big black cylinder ones. Not as nice as a SMU but it should work. And it does do AC current source, I tried it before.This scope is a dog with a floppy drive but I think I can down load the pictures from it on USB floppy.I could document some test voltages. What do you suggest?And I was thinking... is this not exactly the type of problem that might occur from a bad digital control distribution system (with the parts suggested by someone here earlier?). Errant signals throwing the wrong switches during AZ.

author: coppercone2
author_rank: Super Contributor
timestamp: May 08, 2025, 09:56:20 pm
content: Ah darn I thought I found something and it turns out I got thrown off because I was using Q324 as a comparison, and the silkscreen made it look like C324 is Q324 (and they have U324 nearby too, what an annoying occurrence), so I was comparing the wrong transistors. It looks like all the jfets of the type Q312 is measure some low resistance when the circuit is powered off (as JFET are supposed to)Damn tricky bastards I get so excited when i see a transistor that measures low resistance during repairs because there is a good chance you got something. But jfets are different. I thought Q308 was Q324, while really reading the text of C324 and I was comparing the diode test behavior of it to Q312 and I was sure I found a short circuit, until I inspected the package text.They should maybe color the transistor packages. Neon color for JFET. I think that would actually be a nice touch for repair if PNP, NPN, NMOS, PMOS, and NJFET and PJFET. had distinctly different colors if you just want to carpet bomb the board with probe tests. Lets say, Green, Red, Black, White, Neon Yellow and Neon Blue. Or mold them like little chess pieces lol. Of course that never works, I swear I even had new type of wire (manufacturer changed process on wire I was using and I had to buy the new substitutes), molded with two different colors, where black soldered and red pissed me off. I swear the insulation color can make a difference. So it was two recently manufactured wires of the same type in different colors and one of them soldered like a dream and the other one was giving me trouble. Maybe its in my head.

author: coppercone2
author_rank: Super Contributor
timestamp: May 09, 2025, 12:01:18 am
content: And I don't see an option for power line frequency like some meters. It says it automatic

author: coppercone2
author_rank: Super Contributor
timestamp: May 09, 2025, 12:41:22 am
content: 100mV inputbuildings are 700ms long. Distance between end of one building series and next building series is 1 second (occurs every second). So the period is ~1.7 seconds before it repeats.Oh right, and the area between buildings has the 20ms/6ms pulse waveform with 20 ms high, 6ms low. The area inside the building has the same frequency, but its 6ms high, 20ms low. So the duty cycle is invertedI.e. for the 0-5V part, its 20ms 5V, 6ms 0V.For the building part #1its 20mS 5V, 6mS 10.4V.For building 2, its20mS 5V, 6mS 7Vfor building 3 its20mS 5V , 6mS 8.8VI assume that the 5V means 100mV (50% Full scale, and I think it goes to 210mV over range?). The 10.4V is not accurate. Its mad annoying to trigger so I need to zoom in from memory and it loses resolution. I would have to work out all the trigger delays and stuff to be precise.Its still interrupting that measurement alot though wow. 38Hz. I thought it would be more infrequent. I guess its the same as analog chopper amplifier then, minus the crazy buildings. I thought it would do like 1 tiny little interruption every 1 second.The front panel display is like 98.8mV and jumps some where past 100mV every auto zero cycle. On the 34401A the DC out of the 8904A "generator" is 99.98 volts steady. I am using the 8904A set to DC with isolation enabled (it has option for isolated or non isolated source, I use the isolated one via banana to BNC connectors + float setting, so there is no problem with the oscilloscope ground, so there is no ground loop between the front panel ground and the PCB header pin ground). I believe its just a low power DAC/opamp power supply when you set it up like this with the float button and adaptors in DC mode.

author: coppercone2
author_rank: Super Contributor
timestamp: May 09, 2025, 03:00:26 am
content: this is the data. IDK how to view the ISR, CSV or DAT file "nicely" so I just put it on a web app and turned it sideways. its mirrored too for some reason.my drawing is better but w/e

author: coppercone2
author_rank: Super Contributor
timestamp: May 09, 2025, 03:06:24 am
content: and I got a picture after like 20 times with no flash on this POS camerathat is 100mv

author: Kleinstein
author_rank: Super Contributor
timestamp: May 09, 2025, 07:50:09 am
content: The normal AZ mode (as the 34401 and most HP meter use it) is simpler with only signal and zero reading and than taking the difference. This is a bit like an old style chopper amplifier with the demodulation step after the ADC.The K2001 has the extra complication that the ADC uses an extra auxiliary reference and thus needs those extra measurements of the internal reference signal(s).The sequence at AD_in is indeed quite complex (a bit more than I have expected).A assume the measurements where made with a 1 PLC setting. 20 ms is still a bit odd, as this would be more like the time for 1 PLC at 50 Hz, not 60 Hz. There can be a little more of that for settling, but I would not expect that much.The 5V to the ADC should indeed correspond to the 100 mV input signal. The 10.4 V could already be very close to the full scale. The service manual suggests that there is a 1.5 x the 7 V ref. setting (test 300.1) which would be 10.5 V nominal - not sure why only 10.4 V. If so far off I would have expected an error in the 300.1 test.The gain factor should be reasonable accurate (unless there is a HW defect of cause).The 8.8 V should be the 1.75 V internal ref. signal (via PWM, U330,U327) with a gain of 5.There are also 2 short pulses with roughly -100 mV or so. One possibly setting for this could be the 20 V range (would be -50 mV then)I still don't understand why the meter would do so many different test voltages in the cycle. The shorter (~ 6 ms) for the zero readings are also odd, as this would also make it more sensitive to noise and hum. They seem to really trust the shielding that they get not múch hum in the zero reading.It would at least explain why the K2001 is rather noisy and has some extra LF noise (like from the 1.7 s cycle length).It could really help to get the digital data (via GPIB) from the K2001 to see if the variations in the offset correlate with the 1.7 s cycle and how the readings are off. It would be not such a surprise to have slightly different readings in the phase with reference readings. There are things like dielectric absorbtion and thermal effects that can lead to some delayed effect at the ADC.

author: coppercone2
author_rank: Super Contributor
timestamp: May 09, 2025, 01:46:25 pm
content: How and what for the GPIB. Like some program? I think I have a prologix brand USB thing I bought for my spectrum analyzer some whereI don't like hooking up these things to computers, its always trouble, GPIB looks suspiciously like landing craft for invasion. Every GPIB command ends with a question and its slow as hell. Makes me think of sending a bus full of spies into a foreign government capitalDo you know of some recording program or whatever that is likely to connect and work ?>because my other plan is just to replace the MCP's and the comparators, but that is really a brutal approach

author: Kleinstein
author_rank: Super Contributor
timestamp: May 09, 2025, 03:57:41 pm
content: The problem with just replacing parts on suspicion is that it needs a lot of soldering that can add additional damages (e.g. break through hole plating) or solder defects and leakage.In this thread they discuss a program for logging that can work with many meters. Not sure if the K2001 is directly included, but chances are it is compatible with the K2000 / K2002 or editing the changes should be reasonable simple.https://www.eevblog.com/forum/testgear/program-that-can-log-from-many-multimeters/msg2981004/#msg2981004I have not used that program, as I don't have a meter with GPIB and my DIY meter gives out the date in a different format anyway via UART / USB.There could be other such programs around as well.With a high res. meter it anyway makes sense to have a way to log data to the PC, it kind of get boring to write down 7 digit numbers to type in to a file.

author: coppercone2
author_rank: Super Contributor
timestamp: May 09, 2025, 09:44:57 pm
content: that does not seem to be work and I have no idea what to do. I don't know how to deal with high level programs to mod them. I can bearly do some ASM coding and I dont like it. I can't tell if the GPIB thing is working (other then installing the driver) and the program does not seem to detect it and it does not have a K2001 and it does not look easy to mod (i.e. K2000 setting has the GPIB function crossed out)., Programing basically gives me instant psychosis. I already the meter program spitting out computer nonsense like GPIB ADRESS MUST BE GPIB. I can't do this. That guy who wrote it expects you to know how the protocol works, what the naming conventions are, etc. I just have 16. And then you need a whole nother thing.,... the USB thing has some kind of address too. And that would be useful to know if it even detected the adapter.NIMAX bearly works at work with the experts around. We have a special procedure in what order to install things (discovered empircally) so it works with some basic data acquisition. Its really an absurd all day affair to get it working on a new computer WITH the exact guide with the cherry picked driver/module/whatever the fuck it is assortment of executibles . In my opinion that whole 'framework' is flimsy.I think your method for this meter requires someone that likes to code and software things. I might get lucky with the chips. I will carefully replace the MCP chips and comparators.If it had a serial port, I could get data from it, because I got data from 34401A before into excel. But this GPIB layer is just too much bI just spent an another hour looking at this after taking a nap and this GPIB connection is just not going to happen.NIframework:https://imgur.com/gallery/beep-beep-4Qc59zfOk, maybe the NI driver is the tuk tuk and the DIY program is the car. I love that someone made it and had fun. I don't wanna get in itI will also replaceLT1016CS874HC123AM4053MC1455D74HC7474HC00MLM339DLM393DMC14504BMC14052BMC14094BDLM311But I will replace each type and clean and test and go back (spend more flux and time but I can see if something changes)I think that about covers the digital stuff. If the 393 and 339 is suspect, I don't see why to let the 311 and 1016 go. Comparator is digital enough. The LT1016 says its super fast nanosecond comparator. maybe that is more prone to breakingThen I think I should go after any generic transistors if there is any. JFET and OPAMP im scared to touch for now. I don't know enough about JFET and I figure by the time I get to op amps there might be more testing I can do when I am more confident there is no digital part causing confusion.

author: coppercone2
author_rank: Super Contributor
timestamp: May 10, 2025, 05:52:48 am
content: And I can try something else with GPIB if you have another suggestion that is not national insturments NI max or that test program or some thing that requires compiling etc (I see some PY scripts that already raise my blood pressureWindows does see the NI driver when its connected (COM 9 usb port)every time I have to deal with NIMAX its like running away from a mugger and if I see it too many times i am gonna go charles bronson on his ass at work and get fired

author: Kleinstein
author_rank: Super Contributor
timestamp: May 10, 2025, 07:46:23 am
content: One could try to used the 34401 via GPIB first. This meter should have good support. This would one could verify that the GPIB drivers work.Python scripts should be another option, and there are some around for the K2001. I too don't like Python with it's version conflicts and library variants.

author: coppercone2
author_rank: Super Contributor
timestamp: May 10, 2025, 07:51:02 am
content: no it just does not detect the adapter at all

author: coppercone2
author_rank: Super Contributor
timestamp: May 11, 2025, 10:25:18 am
content: does no one have any more ideas on what to probe? I got all these probes I was lined up to measure everything with the best test lead hardware but now its like what to measurepogo pins , chiip clips, micro clips....i can solder things, freeze chips (freeze spray), heat chips, connect wires, knock on things, measure current, drill holes. I even have a logic analyzerHow about busting some traces and seeing if some block works properly? I even have a digital data generator *multi channel* to possibly hi-jack a digitally controlled analog system. I got it because I thought one day I might be able to test something like a DAC based system without programming stuff manually (set with instrument). Damn I think I said a prayer when I just turned that on.And how about ceramics? cracked caps ? I just don't know how it would cause this strange issue

author: coppercone2
author_rank: Super Contributor
timestamp: May 11, 2025, 11:41:17 am
content: BTW there is another detail , maybe.. its not clear but I think I turned the meter on after replacing the caps, and then turned it on again after replacing the DG chips. I think the 'jump' that it had before this DG switch replacement was smaller. I wonder if the soldering process made some tiny fault a little worse and increased the jumping. Because I think it was jumping to 150uV instead of 200uV. But I did not write down anything and it can be in my head. I think I will carefully play around with some freeze spray near the replaced chips (and set the dehumidifer to max). Maybe I will touch up some vias too. Pity some of them are under chips

author: Kleinstein
author_rank: Super Contributor
timestamp: May 11, 2025, 12:04:35 pm
content: It could be worth looking at the offsets for different integration times, like 1 PLC maybe 2 PLC and 10 PLC (longer integration is likely done by avearging anyway) and also the 200 mV and 2 V range.I don't think chracked ceramic capacitors are that likely. It can happen, but is rare. The result would also be more dramatic, like not at all working, especially shorted supply.A possible point to check could be the actual integration time. So look at some signals on the ADC board (e.g. pin 14 of U807 (LM339)) in relation to the AD_in signal.One possibility could be ringing from the main amplifier that is not sufficiently settled when the integration starts.It would need quite some leakage at the DG... switches (mainly U318-U320) to make a difference.A bad soulder joint may be possible. Instead of a freeze spray I would consider local heat. Freeze spary may cause water condensation (unless you have really dry air, like < 20% RH) and an effect this way.Higher than normal input current from the U322 main amplifier could be an issue but would lead to even more effect for the 200 µA range. So I don't think it is the culprit.

author: coppercone2
author_rank: Super Contributor
timestamp: May 12, 2025, 01:22:57 am
content: son of a bitch crazy #$*#$@* I soldered some vias and periodically I would turn it on. I was working aorund u321 and it stopperd jumping!!!!!!!!now its like 2uV offset!!!!!!!! It undulates but I suspect this might have to do with the flux (from soldering vias, not cleaned), the lack of air flow blocking black box and lack of chassis shield. Ima work all the vias and clean it and periodically check every few chips. !!!!!!!!!!!!!!!!! I also reflow one side of a tantalum capacitor bc it got a splash of solder on it and I wanted it to look neat.same fails on amps though. I think I know why, its that fucking ddaughter cardo n plastic standoffs. it needs a fucking chassis bracket instead of this plastic horse shit.I am started to get allergic to these wishful thinking engineering prospects like stacking up cards with little plastic pins that flex a whole bunch of soldered ceramic shit This instrument should have 12 screws and 4 cut outs in the main board to screw on the adapter card. and there should be ribbon cable not header pins that flex the whole fucking assembly like its a prophylactic, and the base plate it screws to should be 50% thicker. The god damn card rests on little chassis "punch outs" on the sideI need to methodically hit every single solder joint on this thing with flux and clean it all off and keep retesting every 20 min work in grid squares.IMO that ADC card is like putting sheep on a trampolineI basically think I can't trust any of the god damn vias on this thing. Looks like a weeks work while rewatching TV shows. I wonder if I can get the amps errors to go away.I knew when I was taking this apart that it has the cheap board dodgey crap going on when the sheet metal guy gets put on the team. I bet the card "smacks" those little chassis protrusions when its impacted bc only 1 screw holds it in place in the middle.I wonder if this problem will be like now its going to be jumping between 0 nanovolts to 1 microvolt or something that is even more annoying and harder to find lolOf course it might just be a solder wisker or something I fried. But The reason I went to that area is because I was looking at how much pressure you need to insert that daughter card and I see that its like flexing everything and I thought this is where its gonna break.Because someone might not pull the tabs pack and just jam it in place after aligning it on the left side for the header pins. That chip is like right thereHow I would do it:1) cut 4 holes in the main analog PCB2) attach 4 standoffs to the chassis3) attach the ADC board to the standoffs.4) attach ADC board to analog board with ribbon cable5) make base plate thicker6) get rid of side tabs on the chassis and use more stanoffs to mount analog boardThen no board is working on any other board, the only stress should be from the connectorThat ADC should probobly even be on compliant mounting if its 7.5 digits no? Like rubber isolators. I don't know about it but it seems prudent not to stretch a sensitive ADCIf you don't know , the analog board is basically mounted the same way you mount your cooking grate in the oven , slide it into sheet metal with little protrusions. I expected something better for a world class measurement range instrument !!!

author: coppercone2
author_rank: Super Contributor
timestamp: May 12, 2025, 03:25:27 am
content: Ok I kept expanding my solder area without cleaning, hit a few of those transistors, etc. I noticed what happens if the board is dirty, the offset goes up. It was at 1uV, after using some flux on the board (rosin mild), and soldering, when it was powered up with the flux still on it (and I am liberal with the flux, I use a rubber point to dab it on the vias (i pour it in a porcelain dish array)) the offset was 6uV. So I see when I dirty the board up the bigger the dirty gets, the higher the offset. I am going to label the re-work I did and very carefully clean the board (though its obvious, my solder joints are like mirrors compared to this shit). I hope to see the offset go down. That means things are workingt the way i think their workingBecasue the first repair work I did wast just with the solder. But its not giving me bright joints i like, so I started using flux, and it looks like more flux = more offset. I am guessing if the whole board is fluxy there might be 60 uV offset (like filthy), at this rate. I got maybe 15% of the vias soldered now. Its really damn painstaking to do thisI have the smallest hakko 'diagnolly cut cylinder" tip I Have, I put flux on a handful of joints, then I put the flat bit with tiny drop of solder on the viaI am scared to keep going without cleaning to verify. If this works out I can do like 30% the next time. Cleaning the flux off is hard. I am guessing its not good to power the board on with flux, I should work 10%, clean it all, then test. I got a few cans of fluxoff (damn that stuff got expensive)

author: Zucca
author_rank: Unknown
timestamp: May 12, 2025, 04:06:15 am
content: Quote from: coppercone2 on May 08, 2025, 07:58:59 amI would check if the above is the same.Moreover I suggest you keep the K2001 in the fail tests so you can measure what is going on. It was my golden way to repair it.I quote the service manual:Quote

author: coppercone2
author_rank: Super Contributor
timestamp: May 12, 2025, 04:34:23 am
content: now that might make sense since the output stopped pulsing, before I felt like it did not make sense to even go after those bugs. But I really think I need to reflow every single via first. Its clearly a problemThe output pulse makes the entire diagnostic thing look like a joke when its occuringthere is even via hidden under the adc board plastic feet if you twist them. god this will take foreverand probobly I should remove every single chip and reflow the vias under them :'(I am guessing.. 900 vias? With cleaning 6 hours work? With the chips like 12? 400 hours to figure out how to connect GPIB?Maybe its time to invest in some ultrasonic cleaning PCB flux wash fluid.Yeah its K2, Kilamanjarno. I imagine a 8.5 digit meter is everest

author: Simmed
author_rank: Frequent Contributor
timestamp: May 12, 2025, 04:59:48 am
content: Quote from: coppercone2 on May 12, 2025, 03:25:27 amin 1 of my previous repair (only 6.5D)i need to wash the board 3 times (using about 1L of alcohol)so wash dry check / wash dry check / wash dry checkinput was over 50G impedance, noise is normalyaybulk 2L or 5L alcohol i think can be had in most hardware store

author: coppercone2
author_rank: Super Contributor
timestamp: May 12, 2025, 05:01:02 am
content: If I really wanna go all out, I think getting under the chips basically requires ultrasonic for peak performance. Need to get a few gallons of wash. But I still need to scrub everything off manually first, as much as possible.Im not gonna let it get ahead of me though, I need to do all the external vias, then try some specific tests (or replace all the digital stuff)

author: coppercone2
author_rank: Super Contributor
timestamp: May 12, 2025, 05:12:35 am
content: And IDK if you know the technique to use less. You bet a flux remover brush (stiff, digikey) and a beaker of alcohol. Pour in like 10ml. Scrub some joints, then dab the brush on a dry cloth to absorb the flux alcohol, dip in the beaker, and keep going till the flux is removed. This will get rid of most of the flux with a minimum of alcohol, it will evaporate off the rag and leave the flux behind.Keep doing this, and you will be left with a wet PCB that looks cleanish. Then you get task wipes, lay them on the PCB, and poke it with the brush to get the alcohol (somewhat dirty). Then used compressed air to blow the alcohol around, to get rid of some of it from under chips, and absorb in wipes. Then you can apply fresh alcohol with the brush (which is drained on the cloth each time before it goes into the beaker, and sometimes you dip it in the beaker without touching the PCB and drain it to flush the brush). I would say you could do that whole PCB with maybe 30mL of alcohol. But of course there will be residual under the chips, then you need to spray flush with flux remover to get that, or spray alcohol can help (but its likely not going to be as good as flux remover).Each time you brush alcohol on the board and soak it up, you dilute the contamination level on the PCB. Just you need compressed air to displace the dirty stuff under the chips for soaking.if you do this, you should need alot less alcohol for the final flush... one way to do it is to dip it in a tray of alcohol (say 1/2 liter) that fits the PCB well, let it soak, then tilt it and use a wash bottle to 'power wash' the PCB while its tilted and squirt it under the chips, working your way down across the PCB.3 Liters sounds a little wasteful. I would be tempted to redistill it to purify because thats some pretty serious money (which is why I really try to minimize the use of flux off, it still feels like you use a whole 19oz can do do a board this size though.BTW I found denatured alcohol (from home depot) works better then IPA because it has substantial acetone content, which is damn good. If you buy spray acetone you will find itdestroysIPA for flux removal. The denatured is impressive (its a tri-solvent mix), but I would still clean it on the end with anhydrous alcohol flushBut damn I want the ultrasonic. Its really the best for cleaning stuff (other then the brush). I just hate how you need to buy the flux remover as a liquid ( i want a concentrate!!)

author: coppercone2
author_rank: Super Contributor
timestamp: May 12, 2025, 05:23:14 am
content: I think ima try ES132

author: Simmed
author_rank: Frequent Contributor
timestamp: May 12, 2025, 05:36:28 am
content: Quote from: coppercone2 on May 12, 2025, 05:12:35 ami know what you meanbut that entire PCB was dirty, so i gave it a baby bath, it was faster

author: coppercone2
author_rank: Super Contributor
timestamp: May 12, 2025, 05:43:39 am
content: there is something to be said about not being exposed to it as long but also somethign to be said for a inefficent process. I really hope the ultrasonic will take care of this once and for all. I have been eyeballing it for a long time. To this point I only have been using it for misc-dirty pCB (i.e. old garage boards) and electromechanical. I never tried it direct for flux removal.The best part is that its aqueous, so no smells, other then a few mL of alcohol to initially agitate itdamn this meter is a trip. They really mean it for every decimal point shit gets crazy

author: coppercone2
author_rank: Super Contributor
timestamp: May 12, 2025, 05:53:04 am
content: After my rudimentery cleaning, it went from 6uV to 2uV. Fluctuate, but it does not look like a pulses. To get it to the same level of clean I had before, I would need to use the flux remover, this was clean with just alcohol and it only had 30 min to dry standing around. Probobly wet under neath.The earlier post seemed to say that this might rely on shielding quite heavily. Anyway when you are going through hell its best to keep going instead of going to take soil samples

author: coppercone2
author_rank: Super Contributor
timestamp: May 12, 2025, 06:01:42 am
content: eatures & BenefitsWater-based saponifier for removing all flux typesFor use with ultrasonic cleaning systemsRemoves encrusted, hard, baked fluxesWater dilutableNonflammableRequires a water rinseRoHS compliantLol this is one of those things that hard to get yourself to buy it. I could not do micro spatulas (useful) or DIP related tools either (amazing). They keep going in and out of shopping cart.

author: coppercone2
author_rank: Super Contributor
timestamp: May 12, 2025, 08:07:39 am
content: What voltage does it typically get if you short out the front panel on short notice BTW? (with auto zero on)If it works right does the auto-zero immediately find it, or it takes like 30 min to go down? In the back of my head I am wondering if 30 counts is a lot or a littleI mean with auto zero on. In a way its more stressful that I got a partial repair because I am worried it will get stuck as a 6.5 digit meter because it never gets the zero down to nanovoltsI did order a gallon of board cleaner.The smaller the problem the more stressful it gets, kind of............ 300uV felt like something maybe you can find. 3uV offset seems like its going to take a miracle to find.Board is pretty dirty right now still (looking with flashlight). I guesss I need to remain calm. Though since the manual gives me the values, I can try to run all the tests and measure what their measuring to loook at the tests that pass too. I just need to finish my plan before worrying about that little offset8.5 digit meters must drive people totallybonkershuh?

author: Simmed
author_rank: Frequent Contributor
timestamp: May 12, 2025, 08:23:11 am
content: my first 6.5D is used unitfrom the old dataset i havethe zero short (100mV scale) 1NPLC is around 0.1 to 0.2uV AZ on** clarification 0.1-0.2uV is average of 900 samples

author: coppercone2
author_rank: Super Contributor
timestamp: May 12, 2025, 08:35:41 am
content: damn thats like a mile off still if the best i saw it is 1uV . I wonder if you can blame that on cleaning. seems like a stretch.Though if dirt got it from 1uV to 6uV and cleaning to back to 2uV and it was kinda half assed clean by your standard of using 3 liters of alcohol perhaps I can sleep tonightshould have gotten same day delivery for 1 gallon of cleaner for $150

author: Kleinstein
author_rank: Super Contributor
timestamp: May 12, 2025, 09:17:56 am
content: The cleaning should not be that critical. The main issue with PCB leakage would be extra input current, lower input resistance, not so much some extra offset.Quote from: coppercone2 on May 12, 2025, 08:07:39 amWith higher grade meters I have used, the offset was often around 1 µV, but it also depends on the quality of the short and shield. The AZ function itself should be essentially instant, maybe 1-2 seconds for the Keithley.With my DIY meter I see some 3 µV from thermal effects and it takes some 30 minutes to stabilize after turn on. Depending on the meter it can take longer (like 1-2 hours). The AZ part is essentially instant (in my case maybe 41 ms for 1 AZ cycles)An residual offset of some 1 or 2 µV is kind of normal. This can happen from thermal gradients and thermal EMF, e.g. at resistors, JFETs, the FETs from the protection and the terminals. Ideally it would settle a bit lower, but how much depends on the details and this can vary between meters. For an internal zero (e.g. shunt) the settling is essentially perfect. The point is that the AZ function can not compensate for offsets from the protecton or other parts before the switching.I don't know how good the K2001 is in this respect, but the protection with FETs is a bit more sensitive to thermal EMF caused offsets.With many meters there is calibration constant to subtract an offset in this order of magnitude. The alternative is for the user to use the rel. function.The AZ partWith the higher resolution meters one has to learn that the last digit is usually not perfect. A 6 digit meter is usually not 10 x more accurate than a 5 digit one and a 8 ditig meter is more like 10 x better than 6 digits. At 8 digits one allways finds some imperfects to hunt - usually not so much an offset, but more INL or reference noise / drift or humidity effects. The number of digits for the better meters is not such a hard classification. The performance is gradual and several points (noise, stability and linearity) have to come together. The keithley 2001 is relatively good when it comes to the stability and maybe linearity, but not great with noise - some 6 digit meters can be better in this respect.

author: coppercone2
author_rank: Super Contributor
timestamp: May 12, 2025, 11:55:07 pm
content: I am at 40% resoldered every via I can on the top. Unfortunately a few MKP caps got soldering ironed on the edge because I was foolish enough to turn on the economic news. It looks like its OK, but my hand started resonating. Some of those vias require some really precise angles. I need a soldering scimitar. I should hit everything from the bottom too for completeness. At least that one is easy and I can anticipate a joint per 2 seconds

author: Kleinstein
author_rank: Super Contributor
timestamp: May 13, 2025, 06:39:43 am
content: I would not resolder too much in one go. One may fix a bad via, bit one could also damage one that is not ideal, but still working perfectly OK.If the offset is small (like < 10 µV and stable) I would consider the main issue fixed. The point is than the do the self test again and see if errors remain there.For the small offset it is than about reading the manual and maybe do a partial recalibration of needed/ possible to trim an offset. Many meters allow for a small offset to be trimmed - this needs a good (low thermal EMF) external short and can thus not be done by the AZ mode alone. Ideally this offset step could be outside the normal calibration. If possible it could make sense to save the calibration data - just in case they get lost or corrupted during repairs.

author: coppercone2
author_rank: Super Contributor
timestamp: May 13, 2025, 08:38:32 pm
content: OK maybe I will give it a rest, I got the parts of the PCB that I feel flex the most when you install that daughter cardthey have a reasonable numebr of those chassis protrusions which the board rests on that seem to focus the flex in a smaller areaif you pull back the wedge on the plastic standoff, insertion force is light. If you don't pull the wedge back its like very high and it "thumps' the board. If a previous repair man did not figure to pull back the wedge I feel like vias might literally be 'hammered 'If they really wanted to use that design the living hinge should have been weakened or they should have put a light spring to pull the wedge back when you push a board into it. The way it works is that at high pressure it receedes and then the board flies down at high speed until it hits the ledgeIf you rotate the white bits 90 degrees you can expose vias right under neath some of them. These will take the full force of the thump. To me it seems like installing a fence post directly under electrical wires in the ground and then beating it down with a mallet

author: coppercone2
author_rank: Super Contributor
timestamp: May 14, 2025, 02:52:18 am
content: I cleaned it with flux remover can and it seems only a few splotches remain (white smears)It was -2uV. I discovered if you put graph paper over the chassis the AZ go within 0.0 to 0.3uV (sometime jump to 0.4). remove it, jumps to 2uV. I know there is still some crud near some chips, I was hoping the ultrasonic will take care of this, or a few more rinse cycles with the can, But Anyway, I think this might mean that its stable enough for other proceduresrear terminals however is -2uV, with the paperWhy is it offset from rear terminals? Maybe something to do with dirt?my short has plastic gripper (its dual banana jack with copper wire short), I am not heating in moving it around (build like good micrometer with thermal isolator). I can repeat this when I push button and swap.or something with the fan?The effect from the paper is sudden, I put the sheet on, then nudge it (so it covers the whole chassis) and then the front panel tanked to 0I don't understand the back panel. The wiring lenght seems almost the same. What the heck is happening here, why is there such a big offset?But anyway, the same errors are in place, for current, ac amps switch and protection.IDK if I should be adding rear volts offset to the repair list? Its teflon wiring, it looks clean and OKHMM actually I looked carefully with a bright flashlight, the wires for the rear panel go behind a relay on the bottom of the board, where the unit was tilted during flux remover spray clean. It does look like there is a substantial amount of white residue right on top of where those wires are soldered to the PCB. I wonder if it could have accumulated there and made it past the wick tissues. I will need to hit that with a micro bottle brush and test again. Perhaps it just happened to really accumulate in that region. Its much dirtier then other areas. Or perhaps flux got into the switch... I can try to spot clean that and tilt the unit in the other direction towards the transformer where its easier to pack wadding and spray clean it again.Hmm but by bottle brush is not ESD safe, and I know that freon can do some really fucking bizzare shit with electricity (and oil too) of the static kind.

author: coppercone2
author_rank: Super Contributor
timestamp: May 14, 2025, 03:29:14 am
content: Also, what error do I want to try to start first with the manual testing ? The amps protection, amps AC switch or one of the ranges?To me it seems that the protection seems like it can effect all of them, making it the best starting point?Since the rear panel is likely a mechanical or contamination issue, and it looks like the front is stabilized so long you have paper on top, I think I can try to do the 'trace'

author: Kleinstein
author_rank: Super Contributor
timestamp: May 14, 2025, 04:13:09 am
content: An error of some 2 µV is easy to get from thermal EMF in the protection part and the terminals. This part can be different for the front and back terminals.For the self test errors, I would consider starting with the amps protection, as this looks like it could be relatively easy (e.g. shorted diode).If just in circuit testing of the diodes is not enough, I would do the self test in manual mode and measure in that state.The AC switch could have side effects on other ranges and may thus be worth working on, at least for the more simpler tests (not random soldering and replacing parts).

author: coppercone2
author_rank: Super Contributor
timestamp: May 14, 2025, 04:19:31 am
content: do you know what page of the schematic amps protection is?https://xdevs.com/doc/Keithley/2001/doc/2001-902-06.pdfI see amps terminal connected to amps ranging.. I am sure I am missing something thoughLike the only place I see amps go after the switch is into the Amps ranging circuit. Is there another one? I think the block is just supposed to say | AMPS | not | AMPS IN | (amps in is something else)

author: coppercone2
author_rank: Super Contributor
timestamp: May 14, 2025, 04:29:26 am
content: Is this the first thing in the AMPS circuit after the switch? Circled in red

author: coppercone2
author_rank: Super Contributor
timestamp: May 14, 2025, 04:37:33 am
content: CR309 looks OK with 0.5V drop in forward bias, and testing the bridge from 309 (connected to bridge corners) and front panel amps in and out seems to show all the bridge diodes of CR305 have a drop of around 0.5 when the individual paths are tested. THey are damn close too, within like 2 milivolts on the diode testerreverse bias shows around a little over 1V for everything, which IMO is pretty normal for in circuit diodesCR323 and CR324 also have something like 0.6 volt drop on them.I see why you find the amps error so interesting. I want to replace U317 again because it totally looks like part of the problem . I should do a pin trace from all the parts of 317 to whereever the circuit goes to make sure there is no degraded traces or something. The path that goes through the JFET is the one that is passing the test I think. Usually I think people say JFET are the worst. I guess I should also probe the switches to see if their control signal is working

author: coppercone2
author_rank: Super Contributor
timestamp: May 14, 2025, 05:28:38 am
content: Hmm the 900 ohm resistor reads as 600 ohms in circuit. But its near alot of analog switches. I wonder if the DMM is causing a problem or if its possibly shot. I guess i need to run a test current through it on the front panel and measure it. All the other divider resistors read OK in circuit. Changing polarity changes it by 30 ohms so it indicates some semi conductor might be causing trouble.,.. protection diodes on the switches or ACA ?Is it time for the HP current sauce to finally do something after the crazy repairs I did on those.... and it has the new output uA range mod on it

author: coppercone2
author_rank: Super Contributor
timestamp: May 14, 2025, 07:10:24 am
content: hMM i did a experiment I am not sure if its valid but I put the 34401A in ohms mode into the amp jack to measure resistance.It only measures 14 ohms when its set to the 200uA range. Not sure if you can probe DMM this way but I can see there is range switching from 2A all the way down to eventually 14 ohms, where the shunt should be 900. The K2 is only measuring 14uA from the meter for some reason... it should be OL? I manually cycle the ranges on 34401a to change the current but it never get past 14uA. It also measures that from a fluke 289 in ohmsmaybe a little suspicious now?I need to get the real current source and just measure it tommorowIts really late and a real long day but I am not seeing why it can't measure the shunt with the ohm metermust be something with all those diodes... I cant be going to the equipment library rnI think for the first time in maybe a decade (or two?) I was thinking that it would be exciting to get up early (to get the current source in the morning) lol

author: coppercone2
author_rank: Super Contributor
timestamp: May 14, 2025, 08:01:15 am
content: Hmm I could not wait so I got a 1k ohm resistor and put it through 1V and put it into amps, I got 14uA on K2001. I put it up to 5V and it was only reading 100uAmaybe something source impedance but I need to sleep before i destroy somethingbut even if its 2k ohms from 900 and 1000, I htink it should be in the mili amps

author: Kleinstein
author_rank: Super Contributor
timestamp: May 14, 2025, 08:34:49 am
content: The low resistance measured for the 200 µA range points to a problem with the amps range switching, like Q311. A bad Q311 could also cause the amps-protection error - so this would definitely be a suspect. It could also be control signals for the 2 A and 200 mA ranges. One could also measure the resistance for the other current ranges, like 2 mA and 20 mA. The higherst ranges likely mainly measure the fuse and switches and not much to learn there.For testing the 900 ohms in circuit, one could use the 34401 in a higher resistance range, like 100 K, so that the test current is low and diodes (e.g. in the DG411 switches) would not contribute much.Normally the 900 ohm shunt should be well protected, so I doubt it is the resistor that is bad.A way to test the shunts and range switching could be setting the DMM to 200 µA range and apply some 200 µA of external current. Than use a separate DMM to measure the voltages along the shunt chain.

author: coppercone2
author_rank: Super Contributor
timestamp: May 14, 2025, 10:00:54 pm
content: right on going up 1 decade for the ohms to 10k got rid of the error and its 900.0

author: coppercone2
author_rank: Super Contributor
timestamp: May 14, 2025, 11:01:52 pm
content: Ok so when its 200 uA range, the signal from the front panel makes it to both terminals 7 and 11 of the U317 chip.The logic input for pin 8 (control of 200uA switch) is 0V when its set into the 200uA range.The logic input of pin 9 (control of 2mA switch) is 5V when its set to the 200uA rangeSo this chip is active low?The resistance from front input to pin 7 (200uA input) is 0.3 ohms with dmm in 2 wire mode (wire, banana jack, test leads, etc).The resistance of the switch for the same range is 18 ohms when measured with 34401A on pin 6So the resistance between pin 7 and 6 when measured from the front panel is 18 ohms. This seems typical. I think this means the U317 switch for 200uA range is fine.

author: coppercone2
author_rank: Super Contributor
timestamp: May 14, 2025, 11:08:59 pm
content: The resistance from the front panel to U317 pin 11 is 0.3 ohms when its in the 200uA mode.The resistance from the front panel to U317 pin 10 is ~90 ohms when its in the 200uA mode. Hmm. It should be 900 ohms.I wonder if this has something to do with that 90 ohm resistor and the JFET. I measured the jfet is closed when its powered off, and thought this means its good. But I wonder if the JFET can be shorted, or some how refuses to turn "on" and close the path.If that switch is closed, then the path to the front panel should be through the 900 ohm resistor and the U317 first switch , so it should be something like 918 ohms. But its like 90. The current has some alternative path that is not supposed to exist at this point. If U317B activated, the resistance should be 18 +-3 ohms by guarantee of the data sheet. So I think it has to involve the other part of the ceramic resistor hybrid. I need to eat dinner and check what the JFET might be doing. First one I ever interacted with. It seems like it might be failing to open. I think either the JFET is broken or the JFET controller is broken or not getting a commandIt says 5432 Jfet, TG-198

author: coppercone2
author_rank: Super Contributor
timestamp: May 14, 2025, 11:47:42 pm
content: I think this is the datasheet for the chip in question in TO92https://www.farnell.com/datasheets/69155.pdfthe 2n5432 is the wrong packageQ311 measures 4 ohms. It says 5 in data sheet for maximum, powered off. I will see what it does powered onIt has 0V on gate no matter what setting amps the meter is in

author: coppercone2
author_rank: Super Contributor
timestamp: May 14, 2025, 11:59:32 pm
content: Damn yeah, it works like it says, the gate is 0V the whole time, and the transistor is conducting the whole time. 0 Ohms from front panel to start of transistor ,4 ohms from front panel to end of transistorSo the 90 ohm resistor is always connected through the JFET Q311!!!! !but why. Gate should be at some voltage for it to turn off. What is going on here. It looks like its connected to U316 LM339 comparator.The 4.7 kohm resistor between 316 and 317 is intact. the voltage before the 4.7k resistor is 1.1mV. I dont think its making a signal. But now its convoluted and confusing, why is 316 not turning off the jfet?I don't think a JFET can short the 316 down to 0.001 volts through a 4.7k resistor. I think that the comparator has a substantial drive capability. And I don't measure any low resistance between JFET gate and grounds. I am thinking to replace the comparator. Then replace the logic chip that is connected to it, rather then trying to decypher that logic..... it looks like all those comparators should have a 2.5V signal going into one thing (its 5V with a 1:1 voltage divider). I can check for the presence of the 2.5V signal, then look at the other signal and see if the comparator is toggled correctly. Then its going to a bunch of 14094s

author: coppercone2
author_rank: Super Contributor
timestamp: May 15, 2025, 12:55:26 am
content: Comparator positive is 2.5V (from the divider)Comparator negative is 5Voutput is 0.001VSo I think it should be that the output is the lower rail, since V+(input) is less then V-(input)But this comparator is +-15V. Should it not be -15V ..... Whhy is it 0V. Should this chip not be +15 or -15VAm I missing something here? I am pretty sure the 339D will output something close to the rails on high/low, regardless if its loaded down by 100k resistor . The rails are measured to be +-15V on the chip. I think the only way this chip could do 0V is if the output is fried and its just leakage pulled down by the 100k resistor?The JFET should turn off from a negative output voltage on the gate.Could it really be a fried comparator?? I wonder why that would break, when its powering a load connected by 4700 ohms. Its like doing nothing, on a dead short its only 3 mili amps through the 4.7k resistor

author: Simmed
author_rank: Frequent Contributor
timestamp: May 15, 2025, 02:37:29 am
content: i guess you need to remove jfetto check comp output if it will goto -15

author: coppercone2
author_rank: Super Contributor
timestamp: May 15, 2025, 02:51:09 am
content: the machine is not flagging any problems after the comparator was replacedI think the jfet is fine

author: coppercone2
author_rank: Super Contributor
timestamp: May 15, 2025, 02:51:52 am
content: Now I will wait for the gallon of cleaner to come in so i can clean the board in ultrasonicAs far as I can tell, one or a handful of VIA and a bad comparator that basically drives nothing at all caused this big messI am not convinced the flux is being removed well under soic chips with the flux remover. Not to the level of these impedances need.Why did the comparator that drives 3mA peak die?

author: Kleinstein
author_rank: Super Contributor
timestamp: May 15, 2025, 03:33:51 am
content: The LM339 comparators in old DMMs have a tendency to fail. It is not clear why - they often don't see excessive voltage or current.The Lm339 may show latch up, that could be triggered (and destroy the chip) when power supply sequencing is not OK (e.g. the -15 V going positive initial, e.g. from load between +15 V and -15 V and the neg supply coming up slow for some reason). Another option could be some poor qualtity batches from the old times.The positive thing is that the comparators are readily available and cheap.

author: coppercone2
author_rank: Super Contributor
timestamp: May 15, 2025, 03:41:14 am
content: the offset for DC I is 7 microamps with a open box, 5 with paperaci is 100nA

author: coppercone2
author_rank: Super Contributor
timestamp: May 15, 2025, 03:47:45 am
content: For DCI, the offset stays at .004 on every range too0.004uA0.00004mA00.0004ma000.004mA0.00004Ai thought everything would explode like highlander

author: Kleinstein
author_rank: Super Contributor
timestamp: May 15, 2025, 04:01:03 am
content: It is normal to have some offset in the AC ranges. The analog RMS chips are limted for the very low end. So it is not just the offset, but also poor accuracy at the very low end (< 0.1% of FS). The observed offset is still well below that.

author: coppercone2
author_rank: Super Contributor
timestamp: May 15, 2025, 04:10:53 am
content: Sorry, I meant DCI.Now its down to 400pA offset DC after being on since the last post. All 0's on higher ranges. 200uA is the worst. Those values should be in pA dohhhhh. not used to being able to see pAFor ACI, ITS300nA, 4uA, 22uA, 220uA, 2mA. So its worse

author: coppercone2
author_rank: Super Contributor
timestamp: May 15, 2025, 04:17:31 am
content: If I switch between ACI and DCI the DCI offset gets little worse. like it was settled at 400pA with some noise, after a switch it seems to dance a littleI am so curious about what ultrasonic wash, di rinse and careful dry will do. I should probobly desolder the relays and the switch for it. I can give that range switch a clean while I am at it toonow actually when I removed the paper is at 000.0001uA unless I move my hand near it. It does not like the fan, having the fan blow on it with the paper over it to focus the air after its warmed up makes it worse!

author: coppercone2
author_rank: Super Contributor
timestamp: May 15, 2025, 04:35:51 am
content: And is there anything about evaluating the performance of relays in this kind of sensitive stuff?Like characterizing settling time, stability or something?Can contact bounce for instance like cause a disturbance perhaps?

author: Kleinstein
author_rank: Super Contributor
timestamp: May 15, 2025, 06:32:48 am
content: The relay switching will inrtoduce some heat pulse and this may need some time to settle. I don't know how long the pulse the latching relays and how sensitive the inputs are to thermal effects. With quite some FETs in the path, it can be a bit more sensitive than other meters.Contact bounce is a really short time effect of maybe a few ms. So nothing one would really see with the DMM.For the residual offset in the current ranges, I would consider the 400 pA very good. The DG411,DG211 and switching FETs can have leakage current in this order of magnitude. So no need for additional cleaning. If one really wants to measure very small currents one should use a special pA meter / electrometer. Even a DIY build with just an OP-amp and MOHm range resistor is not that bad. The difficult part would be range switching.For the relay performance it is about getting a good dry contact, so low resistance already with low current/low voltage (e.g. < 10 mV).Another parameter could be the sensitivity to thermal EMF from temperature gradients. Here latching relays are definitely better than classic nonostable.It is however a bit tricky to find a metric to quantify the sensitivity to thermal gradients.

author: coppercone2
author_rank: Super Contributor
timestamp: May 15, 2025, 06:49:10 am
content: OK I will just try to do a little extra work with freon flux remover to get the white splotches off. The idea of removing the board from the chassis, cutting the current wire (again), desoldering the relays, etc.... its one I can go without if you think those numbers are good enoughI want a new electrometer, I could theoretically buy another Keithley 616, but only if someone has a 100% parts list of what the hell the components are. I have the boards from the old one. The requirement I want is analog output so I can see the signal on a scope. For some reason the 616 gives me anxiety. The boards have a weird coating too. I often wondered about re-making them with some kind of material like Rogers PTFE. I thought one of the newer ones with auto ranging would actually be usable. The 616 has a impressive spec of 200Tohm, but I never really need to measure resistance, and its not worth the INSANE 'knob' it has on it. And the sensitivity settings are confusing too. Maybe I would not hate one that's not dumpster damaged etc, but I still really think I want something newer. And something that would beat the K2001 in leakage of voltage measurement (for working on composite amplifiers that have high impedance, only the K616 kind of worked, when I tried some other meters it would full-scale the thing). But oscilloscope hook up is critical, no BS with computers.Does such a meter exist? I know I can make a adapter box of some kind, but it was kind of cool to have a bench top unit I can plug into it to get a low-effect oscilloscope for things like chopper amplifier feedback loop.And I have no idea how evil repairs or reliability is on a 617, 619, whatever else. If it's the same BS with a list of like 50 keithley only chips, I don't care for it. It will just give me stressThose damn electrometers make me feel like I need to be some weird ass expert in reverse engineering to get anything done. Like one easy mistake and then you have 2 months of work. At least with RF stuff you need to hook up everything etc even if the EQ is complicated (setup is like a big deal)... the EM is just like a benchtop DMM that you probe around with haphazardly when some circuit has been pissing you off enough to turn it on. Usually on a messy bench. At least that's how I would probobly end up using it. I want one thats like robust enough to be a realistic tool. Not sure if it exists yet. I feel like the 616 is something for a physicist that spend like a year working on some radioactive crap to finally install a meter at the end, turn it to some dial and leave it untouched for a decade while it does its thing counting ions or whatever they use it for. Probobly with a complex custom control panel to do anything that needs to be done. Maybe I am saying it has a 'system' vibe. Kind of like those system HP power supplies no one likes to use in a lab (but they are cheap), the size of a VCR with hookup only on back ,terrible UI, terrible display, meant to be installed in a rack mount and remote controlled by a labview program that has 3 head engineers for an assembly line behind it... Those newer EM have the ports on the back, which scares me a little. But it could be HV regulations in industry...

author: coppercone2
author_rank: Super Contributor
timestamp: May 15, 2025, 11:35:32 pm
content: I went through the entire 19oz can of electro wash on this thing (like $40!!). It looks like my re-work and chips I replaced is clean, but a decent amount of white crud came out from under some KS original chips. I don't think its my flux because the stuff I got is usually yellow and when it swells from the freon or whatever it gets like still somewhat off yellow and this stuff is white... so I went through every IC with dash of alcohol on a brush followed by wicking on a tissue and it looks like I finally got it clean after two hours scrubbing it with tiny 'sushi rolls' made out of cotton towel in a pair of very fine tweezers. I don't think these things came out atomically clean from the factory when manufactured.If I could I would get tiny shoe laces tied to tiny strings so I can pull them under the chips too, I bet there is some residual white haze there, on the side I flushed under the chips less. But at this point I can't even tell if there is extra dirt on the wicks. I will reassemble it fully now. I got the area between all the PCB wires cleaned too.

author: coppercone2
author_rank: Super Contributor
timestamp: May 16, 2025, 12:56:28 am
content: I don't think its performance changed very much. I guess that's how it is. I don't like how it seems to be slightly disturbed after switching functions but IIRC the 7.5 digit keysight does the same thing when I was playing with one and a multi function calibrator, and its like 25 years newer..And the ACV noise is 60uV rms..Hmm. Actually the 34401A reads 000.000 mV for AC V when shorted with the same short immediately after power up. I guess that's what people mean by the keithley being noisier? Or is it another repair?And, I wonder how much the drafts in this room are effecting it

author: coppercone2
author_rank: Super Contributor
timestamp: May 16, 2025, 06:08:54 am
content: some hours later the offsets are on the lowest range000.0001 with some jitter on mVDC (left it here)80uV with ACmV-700pA on IDC330nA ACAIf you range switch it looks interrupted. I guess it all has to settle. When I cycled through it and went back to DCv, it was like 800pV offset. I guess this meter needs a do not disturb light on it . And it drops slowly back down. Near the vents I feel the meter built up some heat over 5 hoursAnyway, I think it's good and from experience normal. Other then AC noise. But maybe thats just how keithleys areI left it alone on ACV for a hour, it looks like its 60uV rms now.Not that impressive considering the 34401A is 60x better for offset. But perhaps this is where calibration comes in.If I did not see the 33470 do something similar, I would still be cleaning the board, but I really think that this is just how it is. Because I was trying to figure out why 7.5 digit calibration is so expensive (after leaving a new 34470A on for 3 hours and trying to check it with a calibrated new fluke mFC), and I saw that it is just slow to settle when you switch stuff. It relaxed me a little because I thought that perhaps everyone is gouging, but it looks not trivial. But like a 3.5 digit meter is kinda trivial, and the calibration cost is like if you slice a zero off and divide by 2. And of course if you actually look at the cal sheet, the actual counts to be in spec is much higher then 1, and its disappointing to learn this)I think 1 count is 0.1ppm. But this thing is like 20ppm. It needs to be 200 times betterA 3458A with option 002 says it does 4ppm. But it has another digit. I think we have a long way to go here.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 16, 2025, 07:38:34 am
content: The difficult to remove residue from flux can be some wax / parafine like part of the flux. This is hard to remove, but also not a problem at all, as it is non conductive and more protecting surfaces.Quite some AC noise is normal. The meters are made for wide band AC and have a relatively high impedance (e.g. 1 M divider) at the AC coupling. This naturally includes some noise, especially with a higher bandwidth.If some meters really read a stable zero, this can be an artifact from the RMS chip. The RMS chips are limited at very low signals (like < 0.01%). The RMS chips essentially stop working below a certain level and the output depends on the indiviual unit. It can be zero (neg signal from analog part that the digital parts clamps to zero), but also a different meaningless low value, that could still show a bit noise.The AC input amplifier part looks rather low noise for K2001. So in principle it could be low noise. The problem is likely more the limitation of the RMS chip at low signal and the high bandwith.I think the reputation for being a bit noisy is not for the AC part but more from the extra low frequency noise (e.g. 0.1 Hz range) many of the Keithley meters show in the DC ranges. For the K2001 part of the relatively high noise is from the need to also measure the stable 7 V ref (LM399) due to the separate ADC reference. This needs the extra steps in the AZ cycle and these add noise from loosing time for the main signal and also as noise in the gain. The ADC of the K2001 is also not made for super low noise. The positive points of the K2001 are more the 20 V high impedance range, peak measurement function and high BW for the AC ranges.

author: coppercone2
author_rank: Super Contributor
timestamp: May 16, 2025, 08:25:42 am
content: oh wow so the 34401a might be lying about the AC volts noise? like a discriminator?It sounds like you should use a pre-amp for low volts AC signals on some meters to make sure its in the correct operating range for measurements

author: Kleinstein
author_rank: Super Contributor
timestamp: May 16, 2025, 09:22:06 am
content: It is a well known limitation of the analog RMS chips like used in the 34401 and many other DMMs. The specs are usually only for > 0.1% FS and the performance below 0.01% can get really bad. The limitation is long known, though not everybody is away of this.So there is no such easy way to measure the noise in AC mode.For really small signals one would want extra lower ranges like 10 mV or 1 mV.Another problem with the noise is that the bandwidth with different meters is different and with many of the analog RMS chips the BW also goes down with amplitude.So for really small signals I would prefer an scope or if a reference is available a lockin amplifier.It gets better with digial RMS, like in the DMM6500 , HP3458, KS3446x.

author: coppercone2
author_rank: Super Contributor
timestamp: May 16, 2025, 09:37:35 am
content: speaking of which maybe its time to fix those molten capacitors in the lock in amplifier filter I melted a long time ago (the one that had what look like a battery leak through the vent in the middle of pcb and got mis handled in the oven)all the filters are off by like 5% or more aand the dial meter meltedthat might be a better project then prototyping electrometers

author: coppercone2
author_rank: Super Contributor
timestamp: May 24, 2025, 10:58:40 pm
content: Out of curiosity, if you take these instruments apart, resocket things, solder things, replace parts, etc. How long do they need before it stabilizes. I think I am mainly thinking about the soldering stresses. A month?Like how long should you wait before you try the comprehensive calibration (or maybe a full factory cal)? I imagine things are off-gasing residual cleaning solvents and there is things like screws being at different tension, solder joints pulling and pushing and alot of other changes. It must be a substantial strain to the PCB to under go rework.I believe in this one the reference is through hole, so it is kind of insulated from these things... however none the less there must be something going on in there.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 25, 2025, 05:18:05 am
content: How long it takes to really stabilize depends on the parts. The soldering stress would usually be the same, but it still depends on the temperature in the instrument. When warmer stabilization is expected to be faster.Most meters are made not burned in for a very long time before calibration. So no really long burn in is needed to get to a similar state.I would expect some 24 h of operation to do get sufficient stabilization.A lockin amplifier should not be very sensitive. The point of the instrument is to reduce the need for critical parts. So no special burn in needed for such an instrument.