[yestertech]

Thanks Gents, but sadly it would appear not !!
The fault is now solid and I CANNOT figure out what's going on with this ( expletive deleted ) Unit
So, as 'tis the season to be jolly, I'll offer £10 for a couple of festive beers if anyone can provide any tips which lead to a fix for this dreadful thing !!

I have now :
1. reflowed and checked all joints.
2. "bleep tested" all point to point connections on the copper side.
3. had all the transistors out and checked them on the Peak Atlas - predictably all fine.
4. Checked the mustard cap C9 and the OA5 diode
5. Rechecked all resistor values

I'm 90% certain this is a component fault - The thing is pulling 70-100ma quiescent current, depending on the setting of the variac up to about half mains.This pulls the normal rail volts of 24 down to about 19 v at full mains, so current is flowing around something. There is still a low distorted output.
There appears to be a low resistance path from collector of VT3 to ground ( around 170 ohms ) which doesn't seem right.
There is little or no bias voltage at the base of VT2 - In turn there is very little voltage at the base of VT3
I very much suspect the transistors may be breaking down under voltage, but as I have no substitutes this is hard to prove.
I am tempted to replace the lot with an IC, but even this would take too much time.
In the next 24 hours I will have to abandon this one, which is a shame, but other things are pressing.


Andy

PS If anyone knows any silicon transistors which may make good replacements for this lot, I'd be glad to know...