Hi, I have avt275 about 12-15years old. Problem is when the is switched on there is an immediate buzzing sound, seems to be coming from the amp itself with all volume controls at '0', doesn't seem to be coming through the speakers and remains at a constant volume regardless of any adjustments with channels and volume controls.
The amp can be played through but the buzzing is loud enough to be a problem if mc'd up for stage use.
I've not yet stripped into it to investigate yet, but before I do was wondering if anyone might know what could be causing this and is it a common fault/easily fixable?
Comments
Hello Dave!
Check the power supplies, look with an oscilloscope for AC component content. Also check the supply of the electron tube circuit, if you have a spare electron tube, replace it for a test. Check the soldering of the potentiometers and jack sockets, there may be a ground fault.
The error can also be caused by old capacitors with a loss of capacity.
See the schematic diagram:
https://elektrotanya.com/marshall_avt150_avt275.pdf/download.html
https://elektrotanya.com/marshall_avt50_avt100_avt150_avt150h_avt275_mod...
Good luck with the repair.
Regards: Tony
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