LieboOSBA wrote on 2020-12-09, 16:26:

You can hear normal windows sounds etc through the noise. I assume there is a bad component on the board if anyone can point me in the right direction.

First thing to check in my oppinion: Do all the voltage regulator (P2, likely also U16 and U18) operate properly? If they are voltage regulators (recognizable by part numbers 78xx, 78Lxx or 79Lxx), the three leads should carry

1. the input voltage (+12V for 78-type chips or -12V for 79-type chips)
2. the output voltage (given by the number after the 78/79 prefix: The big 7809 is supposed to regulate to 9 volts; 79-type regulators provide a negative output voltage)
3. ground

The order of the pins is different for 78-type and 79-type regulators, but for the basic check, just seing +/-12V on one pin, 0V on a second pin and the nominal voltage on a third pin is good enough. If one of the small chips is a 78L05, it is possible, although not likely, that the input voltage of the 78L05 is not +12V, but the output voltage of the 7809 (i.e. 9V).

Thanks. I will need to get a multi meter on the pins whilst it is running on a test bench PC then I think.