Electronics > Repair
Please help, FLUKE 8920A Multimeter Repair
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daisizhou:
Hi

I tested again today,I found that if you open the upper cover (upper shell) of the 8920a host,Pressing the "LO RANGE ENABLE" button will have no effect.In other words,When I closed the lid, I pressed the "LO RANGE ENABLE" button, the "2Mhz" indicator light came on, and I saw fluctuating numbers jumping on the display.When I remove the upper cover (upper shell) the "2Mhz MAZ" light will go out,Nothing happens when the "LO RANGE ENABLE" button is pressed.It seems that the "LO RANGE ENABLE" function is related to interference.

To describe exactly what I mean, I shot a video, please watch it


Although I'm not sure if the data is meaningful, I recorded the data anyway
Harry_22:
Probably I found your problem. This is leakage in C18 tantalum.
If I connect 10 kOhm resistor in parallel with C18 the same voltage imbalance is observed.

I attached .CIR file for Microcap below.
daisizhou:
Very good :-+, you have thought of using software simulation analysis.
Should I continue to wait for the fault to recur and then measure the resistance value of C18 online?Or any other better suggestions?
Harry_22:
The voltmeter now shows positive values ​​of 0.83 (or 1.35mV at Low Range). Try applying a hot soldering iron to C18 and check the change in readings.
daisizhou:
Do you mean, let me remove the C18 capacitor and observe the data on the 8920a display? (No components are installed at position c18 of the PCB circuit board)

I noticed that C18 is a 35V 1UF tantalum capacitor
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