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

--- Quote from: Harry_22 on June 11, 2024, 06:56:25 am ---Ether is something that does not exist. This is a medium in which radio waves, gravitational forces and other phenomena incomprehensible to modern science propagate.

So, we have -5 volts from nothing.
Check the resistor R241 -1MOhm.
Look for flux residue around the trace from R241 to JFET Q29.

--- End quote ---
I checked the connection lines, please see the picture.
Most of it is clean, except for the two yellow ceramic capacitors.I used PCB cleaning water to clean the bottom of the two ceramic capacitors.

Harry_22:
What about -5 volt? Still exist?

If yes please connect your DVM through the clip to the trace R241-JFET Q29.
Take the cocktail straw.
Blow through the tube to different places on PCB where the trace runs and observe changes in the voltmeter readings.

There are 3MOhm leakage resistance between this trace and -15v rail. You can see that the voltage is variable every time you measure it: 4,48v 5,2v 5,32v  5,69v
My guess is that this resistance depends on the ambient humidity.
You will try to increase the humidity through a cocktail straw.
daisizhou:

--- Quote from: Harry_22 on June 11, 2024, 08:19:45 am ---What about -5 volt? Still exist?

If yes please connect your DVM through the clip to the trace R241-JFET Q29.
Take the cocktail straw.
Blow through the tube to different places on PCB where the trace runs and observe changes in the voltmeter readings.

--- End quote ---

Q29 -5.14v voltage is always present
I do not quite understand what you mean.

 "cocktail"--Do you mean alcohol?What concentration of alcohol solution?
daisizhou:

--- Quote from: Harry_22 on June 11, 2024, 08:19:45 am ---What about -5 volt? Still exist?

If yes please connect your DVM through the clip to the trace R241-JFET Q29.
Take the cocktail straw.
Blow through the tube to different places on PCB where the trace runs and observe changes in the voltmeter readings.

There are 3MOhm leakage resistance between this trace and -15v rail. You can see that the voltage is variable every time you measure it: 4,48v 5,2v 5,32v  5,69v
My guess is that this resistance depends on the ambient humidity.
You will try to increase the humidity through a cocktail straw.

--- End quote ---

Is C204 C205 possible?Is it necessary for me to remove these two capacitors?
Harry_22:
No, please don't do any hardware manipulations until we find the malfunction.
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