Easy to test: read the PSU voltage levels with the Amiga turned on.
+5V must be on 4.85~5.05 range. More than this and you blow every chip on boards! Less than 4.85 and the Amiga wont boot at all!
+12V rail must be on 10.5 to 12.1V range. It affects drives (HD, floppy, SCSI) and audio.
-12V: same range (just negative, of course). Affect audio only.
-5V: dunno what for...:-?
