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Next round is to look at the multimeter board’s fail-d error. This indicates a problem with reference voltages according to the manual.
Round 2: magic smoke 😢
While I used the scope it suddenly started to have problems on the image: the sides of the image started to crawl to the center. After that I smelled magic smoke, so I quickly switched off the scope.
I fear some component in the PSU will have died.
To fix this I need to remove the DMM board. First remove all buttons from it (use a screwdriver to open them, then pull them back. Then remove the two flatcables and unscrew 3 screws that hold the DMM board connected.
Images for the wiring around the DMM board:
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