PAS3 with PC-7A, Chassis Vibrating
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| Posted on June 9, 2024 at 18:35:33 | |
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Posts: 3
Joined: June 9, 2024 |
I'm working on a friends PAS3 with CAE PC5A, PC6A and PC-7A boards. This was upgraded at CAE several years back. Over time it's developed a mechanical buzz. As soon as you turn on power the cabinet starts to vibrate. The buzz is audible with nothing connected to the inputs or outputs, inputs shorted, and hooked up in the system. If the covers are off you can barely hear the vibration. As you install the top cover the vibration increases, and installing the screws doesn't help. - Replaced the quad cap, no help. - There were no 10 ohm resistors left over from a previous rebuild of the input/output terminals. I corrected that, no difference. - one of the large Wima caps has a crack in the case but it seems to be doing its job of blocking DC and passing AC. Voltages on PC-7A CD - 250.4VDC, <0.2mVAC CB - 287.2VDC, 122mVAC CA - 317.8VDC, 907mVAC 16 - 250.4VDC 0mVAC 14+15,18+19 10.85VDC, 300mVAC Any ideas on troubleshooting this further? My gut is saying it's one of the transformers vibrating but I don't have spares to replace with. PC-7A is two systems on one board, filament regulation and B+ regulation. I was thinking of disconnecting the filament regulation section and substitute with the original Dynaco circuit to isolate that section as the problem.
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