Electronics > Repair

FLUKE 8920A RMS AC meter failure needs help

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daisizhou:
Hello,everyone.My 8920a meter is malfunctioning.

Fault description:
8920a as long as it is not turned on for a long time(Half a month or 1 month),First time booting,The screen displays "700" flashing,Simulate pointer swinging back and forth.Sometimes the "mv" and "V" gears automatically switch back and forth.
Please see the malfunction video-->

,Video of booting in faulty state--->

I don't know how to repair it, if you know please tell me, thanks



Video of normal startup--->


Service Documentatie
www.bramcam.nl/8920/Fluke_8920A_8921A_Manual.pdf

Marketing Folder
www.bramcam.nl/8920/Fluke-8920-Folder.pdf

daisizhou:
I uploaded the malfunction video, thanks

It seems that the fault seems to be related to HOLD/AUTO,(To protect the analog pointer table, I disconnected the pointer table),
See my test video below
https://youtu.be/sO-RI9zRX3c

I'm lost, this is the latest test video, the flashing frequency seems to slow down and eventually return to normal. I don't know where the fault is.
https://youtu.be/zhFRpJvMZdY

daisizhou:
According to the inspection steps in the manual, it is found that the TP201 fault condition is 1.01V fluctuating voltage.

daisizhou:
Can anyone help me? I need help

blackdog:
Hi daisizhou,

Check the Powerrails, are the voltages correct and is er noise on the Powerrails?
There are a number of tantalums across different power rails.
I repaired my 8920 a month ago, it also had bad tantalum capacitors.

Bad power rails can put the processor in the wrong state.

Do you have a Scoop to look at different power supply voltages?

Kind regards,
Bram

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