618 DC HV attenuator failed (no surprise here- I hit it with between 1100~1250VDC while in the DCV AutoRange, yes this was dumb ...
I don't understand this expression..
What exactly happened? Did you apply 1250Vdc when in Ohm mode, or simply when in DCV / Auto mode?
The instrument should withstand such overvoltages to some degree in both modes.
The meter does work in several other functions such as the DCV all except the 100V and 1kV range so I figure it is worth some time and attention. When it is in these two fried ranges it is not accurate at all on low V inputs and only registering 70% of actual higher up ie. a 1000 volt input will only read 700v. (It will not accept a new calibration this far out fyi- I tried this first)
Are 10Vdc, 1Vdc, 100mVdc accurate?
I would have expected that you damaged these lower ranges by applying the overvoltage..
Anyhow, the overvoltage might have damaged the input path, somewhere in between the input jack, ESD circuit, relays K101, L101, K104 , towards U102-A, that is the 100:1 divider.
I propose that you chose 1000V DC range, apply 10V to the input jacks, and measure with your 34361 in high Z mode at first the input voltage to U102-A, i.e. pin 1.
If you don't see 10V, you have to check the components and PCB traces of the mentioned input path.
If 10V are present on the input, check pin12, if the divided 100mV are correct. If not, the input multiplexer, pin 8 of U101-B may have been damaged.
I first thought I blew up the 9.9M and 100k ohm voltage divider resistors in u102-A, but they are fine so I checked all the rest in:
u102-C: 2k, 2k 2k-All Good
u102-D: 20.57k, 5k, 50k, 500k, 1M-All Good.
I assume, that you unsoldered U102, before making these measurements?
I checked all the voltages that I could (attached). I highlighted red only values with significant deviation from what the OP had (Zucca I believe) and in black I have additional readings in case they were to help me down the road, but most of my values turned out to correlate with TiN's working meter leading me to think this IC u102 may be OK?? Hoping anyway. Where my confidence stops is after checking u102-B I get 2k Ohm (pin11-14), 17.3k (13-14), and 84.8k (13-15)instead of 2k, 18k, and 180k. But I didn't really expect any values to be in tolerance since its still in the circuit and I'm measuring resistance which I know is fundamentally wrong to begin with.
Correct, you will only get the proper values by unsolder U102...
Very probably, U201-B is damaged, pushing current from its + input into the node between Q201 and pin4 of U102-D.
This low bias OpAmp in many cases already, fails after years, or maybe the overvoltage killed it, as the 100:1 divider is sitting in the same package U102.
Anyhow, replacing U201 probably will solve this problem.
The second issue I found here is that my output Ohms Current test did actually have 0 current from the low terminal to the anode of CR202. I was measuring with a 77IV so I will try it again to confirm with a 3458 tomorrow I guess just to be sure.
That may also be caused by a failed U201-B
Frank