KEITHLEY 2010 2R / 4R not working.

[tube_lism]

  Hello Everyone...
         I have the problem with K2010. Only frequency reading are accurate and working well. but VDC measure alway reading above 2 time with actual source voltage.
         And when select 2R or 4R the K2010 would be hang up, and press any key will not response, require to off and power up again.
        Temperature mode always shown @ 22.9xx 'C.
 
The PCB look clean, I have to checking DC voltage supply at all point and found are within the range..

*Anyone, please help me to investigate on this problem which parts on the PCB should be specify for checking first. 
 

[TiN]

Welcome to forum. I'd start with running self-test procedure and following with troubleshooting of errors that it throws. Check repair manual for hints.

[tube_lism]

Hi thank for you comment. 
OK, have to done the K2010 self test..
And found a lot of Fails : 100.1 /100.2/101.2/101.3/200.1/200.2/201.1/300.1/300.3/301.1/301.2/301.3
302.1/302.2/303.1/303.2/304.1/400.2/401.2/402.2/403.2
*With short input : 500.1/500.2
 Anyone have error like on these fault code ?

[saturnin]

You have to start solving 100.1 error. It means the multimeter can't perform the A/D conversion properly (for whatever reason). If this is the case, the rest of the tests will fail too. As first thins I would check the main reference (LM399) and infamous resistance network TF-245 (R271).

You can use Keithley 2000 service manual and schematics as a good starting point (since its ADC section is quite similar to 2010 model). At some point you might end up with reverse engineering of 2010 circuitry. There are schematics available for 2010 too, but they are not so accurate/complete...

[picburner]

For the error codes the Keithley 2000 repair manual can help you a little (the K2010 repair manual is not on the web).
Some error code is missing but it is better than nothing.

[saturnin]

Keithley 2010 service/repair manual is available too (directly on Keithley, ehh Tek website: https://download.tek.com/manual/2010-902-01(D-Oct2003)(Service).pdf), but it lacks built-in tests description. Still, it can be useful since it contains block diagrams and tables with the analog signal switching states...

Luckily, models 2010 and 2000 are quite similar (the main difference is the low noise input section in K2010), so one can repair K2010 even with the K2000 service documentation (personal experience) 

[tube_lism]

  Hi, many thank for all guys comments 

I have tried to checking and focus on around TF-245 and U139 first, then LM339 Ref...

On K2010, not sure the voltage quite difference from K2000 schematic or not ?

Using DMM to AGND TP-102 ..

U141 LM399...Ref voltage...
pin1 : 3.672 V
pin2 : GND
pin3 :+15.20 V
pin4  :-15.98 V
 
U139
Pin1: AGND
Pin2: -15.99 (-Vcc)
Pin3: -1.275
Pin4: -1.345
Pin5: -0.983
Pin6: 15.820 (+Vcc)
Pin7: -9.58
Pin8: -1.054

*It possible U139 have to defective, i feel quite hot by hand touch ?

On the attached image seem the +V to TF-247 below the range ?

[TiN]

I would perhaps remove U139 and test if you get +7V out of LM399.

[Kleinstein]

U139 is highly suspect.

The Lt1124 has a relatively high power consumption (around 4.5 mA), so a slightly elivated temperature is normal.
There is also slight chance that the circuit around U139 oscillates and this way create the odd lokking voltages.

Instead of the LT1124 a more common LT1013 can be possible replacement with the same, non standard pin layout - it is even slightly lower noise for the relevant low frequencies.

The voltages around the TF245 should be relatively similar to the ones at the K2000, but with the extra zener diode somewhat (e.g. 8%) lower.