Author Topic: Keithley 2001 Repair Log (Making Progress Now. Unit Powers On.)  (Read 1364 times)

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Offline FRR

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Keithley 2001 Repair Log (Making Progress Now. Unit Powers On.)
« on: September 14, 2018, 01:46:52 am »
I picked up a Keithley 2001 for reasonably cheap a while ago and finally found some time to start working on it. Unfortunately someone has already been inside the unit since the ADC board is missing along with a few components from the analog board.

When I first received the unit the fuse was blown so I took a look inside. Not surprisingly the capacitors had leaked and covered a very large region of the board. Unfortunately it shorted CR109 and CR110 creating a little explosion. I went ahead and disconnected the transformer for that part of the board and powered on the unit. It powered up so now I knew at least some of it still works (screen & digital board).



I pulled the analog board and de-soldered all the capacitor. Only C114 leaked all others were good. Interestingly C114 was 2 years older than all others and had the older style seal. Once I removed CR109 and CR110 I needed to clean out all of the burned area as that is conductive and it can't be left there. I carefully lifted two pads so that I could thoroughly clean everything out. There are three traces running through that area, but lucky I was able to clean everything without much fuss. The damage is almost going through the entire board. This will later be filled.





The next step will be to check all traces / vias and make sure nothing is broken as I don't want to end up chasing my tail later. I still need to remove some additional components from the board and do a through cleaning. I also need to source the missing ADC board. I have already started a parts list of what all is needed and will place the order soon.
« Last Edit: October 04, 2018, 06:23:27 am by FRR »
 

Offline TiN

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Re: Keithley 2001 Repair Log (Need ADC Board)
« Reply #1 on: September 14, 2018, 05:05:55 am »
I maybe have one ADC but it need some parts (DG4xx switches and some JFET perhaps).

Also it's a bad idea to power on meter with open traces in that area, because that part of circuit is bootstrap capacitor multiplier supply. Chances are that now you killed bunch of opamps/parts in input front end which uses boostrapped +38/-38V supply to provide high impedance input that this meter have.  :-BROKE
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Offline FRR

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Re: Keithley 2001 Repair Log (Need ADC Board)
« Reply #2 on: September 14, 2018, 05:24:05 am »
I maybe have one ADC but it need some parts (DG4xx switches and some JFET perhaps).

Also it's a bad idea to power on meter with open traces in that area, because that part of circuit is bootstrap capacitor multiplier supply. Chances are that now you killed bunch of opamps/parts in input front end which uses boostrapped +38/-38V supply to provide high impedance input that this meter have.  :-BROKE

I must have explained it wrong. I never powered the unit with the parts removed. I powered the unit before removing anything from the PCB and I disconnected the transformer from the analog board so no power was going through that area.
 

Offline FRR

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Re: Keithley 2001 Repair Log
« Reply #3 on: October 04, 2018, 06:23:01 am »
I managed to acquire additional parts (including an adc board) needed for the project so making a bit of progress now. The PCB was repaired and all missing components have been soldered into place. Now was a good time to power up the unit and see where we are.





The unit powered on without any issues, but when running self test there were 11 errors. Not too bad.

304.6 ohm
304.7 ohm
405.2 abs ckt
405.4 abs ckt
405.6 abs ckt
407.1 front end
407.2 front end
407.3 front end
410.1 trms
411.1 trms filter
411.2 trms filter

Now that I know the boards are functional at least to some extent I am going to remove a large area of components cleaning any remaining contamination on the board. This will require a very large amount of components to be de-soldered and re-soldered. Below is a picture of where all I found electrolyte from the capacitor leaking. I have considered putting this into the ultrasonic cleaner, but I am not sure it will get everything out from under all of the SMD components.

 
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Offline coromonadalix

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Re: Keithley 2001 Repair Log (Making Progress Now. Unit Powers On.)
« Reply #4 on: October 04, 2018, 10:37:46 am »
Not sure i would go all the way to remove parts, you may create more problems, i would focus on the remaining problems if there is, after a good cleanup.

You have good cleaning products who can go under the parts and do a very good cleaning.

At my job we use liquid flux who goes everywhere, we rince to board fully after in de-ioniozed hot water with Atron SP200 and or Atron AC205, it remove any greassy stuff and flux residues, and with air spray we remove any water excess and put it in an pcb dryer.
 

Offline Le_Bassiste

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Re: Keithley 2001 Repair Log
« Reply #5 on: October 04, 2018, 07:23:31 pm »
I managed to acquire additional parts (including an adc board) needed for the project so making a bit of progress now. The PCB was repaired and all missing components have been soldered into place. Now was a good time to power up the unit and see where we are.

I have considered putting this into the ultrasonic cleaner, but I am not sure it will get everything out from under all of the SMD components.

well, unless you have definitive information on all exposed parts being suitable for ultrasonic cleaning, just don't do it.
as coromonadalix already said, proper (and repeated) cleaning will most likely do the trick. i can confirm that from my own repair experience on several stone-old 200x units.
patience is the key.

« Last Edit: October 04, 2018, 07:26:01 pm by Le_Bassiste »
 

Offline TiN

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Re: Keithley 2001 Repair Log (Making Progress Now. Unit Powers On.)
« Reply #6 on: October 06, 2018, 01:47:15 am »
If that would be me, I'd go with desoldering/cleaning/soldering new components (not old ones! When not custom parts) path. With care and patience, it does not sound so bad. Also meter must need full recalibration anyway, so that doesn't matter anymore. 304.6/304.7 errors are often result of excessive board leakage, cleaning of ohms area and area around switches near LTC1043 may help on those.
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