Fluke 8920a Voltmeter Repair Need Help

[daisizhou]

Hello everyone,My fluke8920a voltmeter has been under repair,It's malfunctioning very strangely,I tested it for a long time,it's still faulty now.

Below I will describe its failure phenomenon,After power on,Press the "LO RANGE ENABLE" button，The analog pointer keeps swinging back and forth,I don't know what's broken.
I try to plug in a 50 ohm load,And press the "LO RANGE ENABLE" button again,The malfunction is still the same.
In order to explain the fault more clearly, I took a video,Please let me know if you know or you have the same glitch, thanks

https://youtu.be/l_2e7JcHB2g

repair manual-->https://www.elso.sk/media/download/pdf/fluke/man/Fluke_8920A_8921A_Manual.pdf

[daisizhou]

S202 switch

[coromonadalix]

check the logic going into U205, it may have been damaged

[daisizhou]

thank you for your reply。I checked U205 it is working，Sometimes press "LO RANGE ENABLE" it is normal, sometimes it is faulty
I wiped the motherboard with ethanol and baked it, the fault disappeared for a while, but the fault reappeared after a while