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Hi, I have a stage 160 which came from another engineer who gave up with it. If you switch it on it has what sounds just like AC mains buzz through the speaker, more buzz than hum if that helps? No fuses blowing, no excessive current draw (Im running through a limiter lamp which is glowing but only very dimly which it sometimes does with a big transformer anyway). No audio coming through, controls make no difference whatsoever. It sounds like its about to blow up but it will happily sit there with nothing overheating if I let it.
Thought the obvious of main smoothing caps but nope, mains rec diodes all check ok. All low voltage rails measure correct and all channel switching lights etc work ok.
I know these amps are prone to smoothing caps and cracks around them but there is nothing.
Only anomaly I can find is the main HT rails are low at around 38 volts when they should be 45 (+ & -). Checked out all six output transistors and all check perfectly ok.
Board and all soldering is clean and in good condition, no dodgy previous repairs etc.
There is no DC on the speaker output and about 0.2 vAC which is the buzz.
Its so pronounced Im sure I must be missing something obvious. Ive attached the schematic. I think!
Any thoughts appreciated.
Thought the obvious of main smoothing caps but nope, mains rec diodes all check ok. All low voltage rails measure correct and all channel switching lights etc work ok.
I know these amps are prone to smoothing caps and cracks around them but there is nothing.
Only anomaly I can find is the main HT rails are low at around 38 volts when they should be 45 (+ & -). Checked out all six output transistors and all check perfectly ok.
Board and all soldering is clean and in good condition, no dodgy previous repairs etc.
There is no DC on the speaker output and about 0.2 vAC which is the buzz.
Its so pronounced Im sure I must be missing something obvious. Ive attached the schematic. I think!
Any thoughts appreciated.
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