Tektronix 2430A occasionally fails some tests

user920
 

Hello, I recently bought this oscilloscope as partially working, the owner said it worked fine but once it failed some tests (PA and TRIGS). At home, no errors appear and the scope seems to be working. While I was trying some signals using an android app for function generation, the signal disappeared from the screen. I proceeded to make the self diag and there were two fails (CCD and PA, all relative to gains). Here are the pictures: https://imgur.com/a/DNgRcPG
After I restarted the scope, however, there were no errors and I continued to test the scope without trouble. I am not sure what the problem can be, if there is any. Do you have any ideas of what I can check? Thank you

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