Keysight 34450A Help

[Louis_C]

Hello all. I'm looking for some help on a Keysight 34450A. All calibration tests pass except for 100mV AC @ 100kHz. It reads 94.837. The Low limit is 96.700 and the high is 103.3. I tried performing the internal calibration and entering the new corrected reading for this test point and the unit rejects it and fails. I flashed the firmware to the latest version available ( 01.03-01.02). I'm not sure what else to do here. Can anyone give me some advice as to what to look at next? Thanks!

[Greybeard]

Are you sure your source voltage is correct?
Have you checked with another DMM?

[Louis_C]

I had the 34450A connected to our Fluke 5500A during the internal cal/adjustment procedure.

[floobydust]

Is the ACmV reading stable?
What about different (lower) frequencies. What about linearity - how is it at 25, 50, 75mV; still -5.16% ?

We don't have a service manual or schematic to troubleshoot the ACmV path, and it's a custom DMM IC. Right to repair nah.
The relays are kinda cheap so try working them, I don't think they have a lot of palladium lol. But I think the cmos muxes are doing the range switching work. If it was grossly overloaded on ACmV the H/W could be damaged, that's why I suggest seeing if it's just a span problem or more.

There are two firmware loads - CPU for the main and MCU for the DMM portion and not sure if any F/W update covers both processors.