Keithley 2000 repair [Solved], but with my own induced booby trap

[Satbeginner]

Hi all,

I just want you to inform about my self induced Booby Trap while repairing a nice Keithley 2000 I bought on eBay "for parts or repair"
I don't know what they did with it, but man, soo many things were broken....

It gave about all errors during the selftest that exist, 100.1, 100.2 101.2, 200.1, 201.1, 400.1, 500.1,  etc. etc.

First I did check and replace the power supply capacitors, although they looked OK, but since they are the usual suspects, better safe then sorry.
Supply voltages were OK, but like I said, all the Self Test errors were there.

I started with the first error 100.1 :
As stated in the repair manual one should start looking around the reference, Supply Voltages, and then U163, U165.
Long story short: the were both "dead".

I ordered a long list of replacement parts at Mouser, and during this period I sensed that U137, U138, U142 and U145 were getting really hot, so I ordered these too.
When the Mouser stuff arrived, I replaced the removed parts, double checked my soldering work and powered it on.

Within one second U163 (the Analog Selector Switch) sort of exploded with sparks and smoke..... 
Oops, what to do now: I removed the remains of U163 and powered the unit on again (without U163) and things looked OK-ish, that means no sparks, no smoke, levels measured at the pins of the U163 location looked normal, so, WTF??? Was it my soldering after all??

OK, I got courageous, and put in a new U163, crossed my fingers, and POOFF!!! Again minus one on the scoreboard.... :-( WTF !!

I checked the partnumbers, and they were OK, but were they really??
The original U163 was a DG408DY, the ones (two..) I got from Mouser were labeled DG408LEDY ?? Could this be important??

Oh Yeah!!

The original part (DG408DY) has a +/- 20V rating, my parts (DG408LEDY) only have a +/- 8V rating!!! and U163 get both +15V and -15V as power supply
It was my own mistake, I ordered the wrong part 

I corrected my mistake, and a week later I was able to continue my search.
The 100.1 error now was solved, but the next one was 100.2.
They were all related to U132, U166 and U129, they were replaced as well.

There were more errors, like 101.2 etc., they were related to U137, U138, U142 and U145, and finally, there were some fine tracks on the board to and from the Front/rear switch that were missing. (400.x and 500.x)

I replaced the switch (also Mouser) and corrected the missing connections.

In the 2000 design, Keithley made sure only low current connections run through the switch, the Common and Amp wires are directly connected to the board.

Although it was very close (within specs) to both my HP 34401A, HP 3457A and the other K2000, I did a DC calibration, mostly to check if that would work without errors, and it did.

The good news: I now have a second K2000 working as it should be.

I must say, the way Keithley has documented the repair steps is (IMHO) 200% perfect!!
It takes you step-by-step through the meter.
If you run the diagnostics in the "Pause on error" mode, they specify the control signals, tell you were to look for them, etc.
This, with the help of the reverse engineered schematics, makes a repair very well possible.

This is a great source for repair info on the Keithley 2000: https://xdevs.com/fix/kei2000/
Especially this repair manual: https://xdevs.com/doc/Keithley/2000/2000-903-01_B_Dec_1999_QRG.pdf

Great work, well done design people at Keithley!

Un saludo,

Satbeginner (Leo)

[alm]

Funny, I usually found Keithley service documentation inferior to HP. Less detailed theory of operations. They stopped publishing schematics (both component level and block diagram) earlier and even removed schematics from some old manuals available on their website. The only positive is the (partly reverse engineered) schematics for the Keithley 2000 and 2001. But good that the Keithley 2000 documentation helped you!

[Samogon]

Maybe he didn't deal with hp/agilent 34401a which service manual is handbook for repairs snd service.
Also calibration procedure of keithley is quite complex if done manually, compared to 34401a