This may or may not be relevant but I have also had an irritating crackle in both speakers, independent of volume for many months but hadn't got around to investigating. Could this be something on its way out which has finally gone.

Odd that it came back to life just once last night.

Open it up and see if something looks suspect - remember to disconnect it from mains.

If you are lucky, it could just be a blown fuse. Otherwise, I would suspect capacitors on the power board first.

A blown fuse would be lovely but it came back on briefly and fuses, once blown, tend not recover.

Really need someone's help. Had it in pieces, power in rectifiers checked out fine, as did main power caps and many of the transistors around the main power in circuits. Decided to put it back together to see if I'd disturbed anything for the good and am still getting no front panel lights but a constant noise from the speakers like very distant machine gun fire or a fast tickover diesel engine. 

Can anyone point me in ANY direction 

Please !

Bad capacitors in the low-voltage power supplies, dead voltage regulator and/or dead CPU.
Some versions have a fuse on the processor board, check it if present.

Martin

There is a fuse but it's ok, still trying to FIND a voltage regulator !

By low voltage circuit I assume you're referring to the 5 volt circuit supplied to the microprocessor board ?

All voltages apart from the ones feeding the amplifiers.

The voltage regulators are on the cooling fins, right side.

Martin

On the cooling fins I've got 4 Darlington transistors, which I assume are 2 for each channel, and 4 standard transistors TR5, 8, 13 and 16. If I'm missing something obvious please forgive me.