Keithley 2000 - Self diag fault 402.2 - Resistor ID?

[Macbeth]

Recently got a Keithley 2000 which consistently failed it's VAC test 402.2 in the self diag. I also found its AC volt measurement were around 4% out, while the DC is pretty much bang on within 0-2 counts with my chinese Hao Qi Xin volt ref.

I'm posting this because at least 2 others on the internet have had the same fault but not appeared to resolve it or document resolving it. Also, I wouldn't mind part identification too.

I pretty quickly found SOT23 resistor network R110 was reading 1.6k instead of 1k (in-circuit) on one if its resistors. There is another one of these devices nearby, R133 which read 1040 ohms in circuit.



The repair manual has a description RES NET, 9K-1K, MICRO DIVIDER and Keithley part number TF-246-2. As can be seen in the pic, its only identifier is A4E

Anyone have any idea what it is? The best I can come up with is Vishay MPMT10019001.

Before I get the right part I decided to bodge the existing high 1k6 junction with the closest to get it to 1k I had on hand - a 3k3 0805 in parallel.



  It appears to have fixed it. Measures 1070 ohms in circuit and I have ran the VAC tests in a loop for an hour - no problem.

I still have a 4% out on 10VAC range readings, so I guess a DIY recal is in order on the VAC only. When I get the proper part I may get a real calibration/adjustment.

[ketil b]

Hi

I had a similar problem but with R133 winch is the same part. It meant that U112 had a gain of about 8 instead of 10

I replaced it with a Vishay Thin Film MPM Divider,

thanks

ketil

[Macbeth]

Thanks. Confirmed what I thought it was. I've calibrated the low AC ranges up to 10V using my sig gen. I don't have 100 VAC or higher to play with. The high range seems to read ok (240 VAC makes an easy test  ) and all my low ranges now match up with my other meters and scope give or take a few counts.

Have added the proper part to my digi-key/mouser want list to be ordered when it eventually tops £50 

[Macbeth]

Necro update:

Vishay MPMT10019001 is the wrong part as it has the 9k/1k the wrong way around 
The correct part is MPMT90011001 as I found to Vishays cost thanks to their sample service 

It also seems the newer Keithley 2000 meters have a totally different (through hole?) SIL package instead. Perhaps the older SOT SMD's were not up to snuff?