Keithley 2001 with burned analog board.

[overvoltage]

Hello everyone,
I recently got this Keithley 2001 that would not power on.
I checked the fuse and found it was blown so went inside to investigate.
The fault was easy to spot as it had burned the PCB right below the power input jack.
Two SMD resistors (R123 and R250) got so hot they charred through the board. (Shematics and Pictures attached)
Obviously I want to save the analog board and thankfully this is the least densely populated area.

R100 reads open so the thermal fuse in it probably got triggerd, was this heat transfered from R123 and R250 or is R100 involved in the fault?
I suspect VR100 went short and overloaded these resistors, Q528, Q101, R102 and R103 seem fine so I doubt VR101 was directly involved.
The transformer thankfully appears unaffected so it does not seem like the fault lays on the secondary side, that inspires some hope.

How do I clean this board properly to check the traces?
Any insight into the cause of this disaster?
What is the appropriate cause of action? Desolder all components in the general area?

PS: I know all Electrolytics in this meter need replacement but I dont want to invest into a new set of caps until I can power it on to check the precision analog section.

[Kleinstein]

This looks really burnt. The chard black part of the PCB may be no longer isolating. So it may may need something like a dril or dremel to "clean" / cut away the bad parts.  So get to the area one would need to desolder a few parts, like the MOSFET, even if not brunt.


For the cause of the desater I see 3 possible scenarios:
1) the automatic 110/230 V dedection did not work and did not switch the relays right
2) a relay of the 110/230 V switching got stuck
3) supply voltage was too high or maybe frequently switching on off (e.g. bad cable) to cause the switch over to fail

I think the 110/220 V switching by relay deserves a few extra  .

[Gyro]

What ridiculous complexity! 

As you're in the EU, wouldn't be simpler just to depopulate the area and hardwire the transformer for 230V mains?... or am I missing something?

[Kleinstein]

Removing K101 and hard wire to 220 V is likely a good idea to reduce the chance for future damage. The root cause may be on the control side, or maybe a stuck relay.

K100 has 2 more settings for the voltage. Likely something like 220 and 240 V.  Chances are the input circuit would survive if K100 is in the "wrong" setting. So I think it should be OK to keep K100.