Re: Marshall Stanmore Repair

Hi.

I have tried to move the transformer between the two and the whining is not moving. This means that it is not the transformer that is "faulty". If i remove the rectifier diode on the 14V line that feeds the LM817 the whining disappears. Everything is working so what can be wrong, maybe something on the 5V?

Regards

Re: Marshall Stanmore Repair

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Re: Marshall Stanmore Repair

Hi.
I have successfully repaired two stanmore. Both had identical faults. 220 ohm resistor to optocoupler burned. I have replaced all capacitors on the hot side. I have changed Mosfet,pwm ic, various resistors including 0,1 ohm shunt. I have replaced everything between pwm ic transformer output and the pwm ic. All diodes except the full bridge. All rectifier diodes after the 3 transformer output. 7812 and power amplifier. Both are now working but one of them have a high pitch transformer whine that also leaks into the sound. If I mute the sound...