Electronics > Repair
Please help, FLUKE 8920A Multimeter Repair
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daisizhou:
I measured all the transistors in the area,And the resistance value is less than 800 ohms.

I checked all areas pointed by the green arrow,Does the area with the red arrow need to be inspected?
I have marked the location points and resistance values in the green area. Are they abnormal?
Harry_22:
You measured JFET transistors they are used as relays here. The low resistance is Ok at normal (disconnected) conditions. Q28 and Q29 are in low resitant section and also in parallel it is possible to have about 40 Ohm.
You malfunction is impermanent. It is very hard to find because all parts are good for a long time.

Please check if falure persists if you press "LO RANGE ENABLE" button. If yes plase measure the same voltages:
TP1:
R40:
R41:
R42:
C24:
daisizhou:
My original plan was to disassemble these 120 ohm JFET transistors,Detach the PCB circuit board and measure to confirm whether it is normal.After reading your message, I suspended this plan.

I don’t know why, but today the 8920a always turns on normally.What I mean is that when I press the "LO RANGE ENABLE" button, there is no fluctuation.I have been waiting for the failure to appear, preparing to test TP1, R40, R41, R42, C24

The fault appears to be the same as what you described,Much like the capacitor aging, the leakage current,All I can say is it looks like,But for the power supply, I tested the electrolytic capacitor offline and confirmed it.In the signal part, many are red tantalum capacitors and ceramic capacitors.
(https://www.circuitsonline.net/forum/view/165140)I noticed this author "blackdog" who had trouble with tantalum capacitors.It looks different from mine. What I mean is the malfunction.

Now I can only wait, I'm confused........ :-//
Harry_22:
It is a normal situation. Currently I am waiting for RF amplifier malfunction more than a week. it is very important not to do any manipulations with the hardware while you detect and localize malfunction.
Please don't unsolder any parts including capacitors.
daisizhou:
ok .i will wait for the error to appear again
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