Need help repair Keithley 2000

[f14]

Hi All,
I have problem with my Keithley 2000, Yesterday It work normal then suddenly the message " OVR FLW" appear in screen . in all DCI/DCA ,ACI/ACA ,Ohms , 2& 4 W
I open it and check power supply -15v , 15v ,5v is normal , no burn , no fire , smell normal
So what wrong with this ?
Thanks for help!

[Zucca]

Self Test? What errors is the device reporting?

[f14]

 Thanks for you reply
  have a lot of error code
100.1 101.2 101.3 200.1 200.2 301.1 301.2 302.1 302.2 303.1 303.2 304.1 400.2 401.2 402.2 403.2 600.1 600.2 601.1

[Johnny10]

Service Manual:

https://www.tek.com/digital-multimeter/broad-purpose-digital-multimeters-manual-5

[nidlaX]

So DCV and ACV working?

[f14]

DCV and ACV are not working . with a message OVER FLOW error on screen :|

[saturnin]

Since it displays OVER FLOW on the display, the ADC probably sends some data to the main MCU. Start debugging 100.1 test. Run it in "step mode". When the test is "paused", press SHIFT button and the result of the test will be displayed. What value does it show?

As the repair manual states there are several reasons 100.1 test fails: something could be wrong with A/D MUX U163, the A/D buffer U132 and associated circuitry, or almost any component in the A/D section. 

[f14]

Hi Saturnin
It show "Overload"
I will check  other error code . May 7V source have problem?
Thank for your help.

[saturnin]

Yes, references (+7V, +14V, -14V) are a possible suspect too. Read the 100.1 test description in the repair manual thoroughly. There is mentioned what components you should check. Schematics are also available: https://doc.xdevs.com/doc/Keithley/2000/K2000.pdf

[f14]

I have read repair manual about error code 100.1 and 301.x and check the voltage
after check two resistor R194 and R195 the voltage in R194 is around 19v in both end  ( normal is 14v and 7v?)
R195  is ~19v and other end is ~16v   
 I will desoldering TF-245 to measure value
Thank you!

[saturnin]

If you measure ~19V at common node of R195 and R194 then auxiliary references +/-14V are not working properly. Check R271 (TF-245), U139 (LT1124), and U141 (LM199). TF-245 is notorious to fail, but I've seen LT1124 and LM199 failed too...

[f14]

Hi All,
After measure TF-245 (compare with sheet https://dev.xdevs.com/issues/1178)lucky it normal
I just order Lt1124 and Lm399 . and waiting

[f14]

Hi All
After few week . I received some part for fix my k2000
First I replace LM399H(U141) and TL1124(U139) . good have 7v and almost 14v
But problems "OVRFLW" still appear . nothing better
Second I replace all U166, U132, U138, U137 and MUX U163 . and check some diode CR105 108 around AD section but dont have any better
In AD in (TP105) measure 0V in all self test ( first 100.1 )
Have any ideal ? Only U165 I cant replace
Thanks all

[f14]

New update. After remove  U133 (DG444DY) but i dont have this ic. So i replace by ADG412 (i know nothing change if add this ic  )from 34405a board. And self test 100.x and 200.x is pass. So i think problem is there.
now i order new dg444dy for replace

[Kleinstein]

The difference between DG444 and ADG412 is not that large. So even with the ADG412 the meter should kind of work (maybe lower performance, but still pass self-tests).

It is a rather odd way for a repair, changing parts more or less at chance. Especially changing the LM399 is one thing one should avoid, as this would definitely require a new calibration and the LM399 is likely not just an of the self version but a selected one with burn in. So one might consider changing back to the old 399. It would have been easy to check if LM399 is still ok even in circuit.