Well, started with following the grounding scheme through the amp, and I suspect there may have been a Muppet in there, didn't take long to find the missing link so to speak, the regulated supply board now has ground reference, so once I sorted that I was able to trim the voltages up to perfect, then of course everything fell into place around it, so the power amp is running well now.
We have an issue when the Head amp boards are installed, I am about to check these out to find what the issue is exactly.....There's some kind of imbalance putting huge DC through the signal path...
So anyway, working away methodically from the top to the bottom....I am praying I don't have any of those small relays playing up, that is not going to fun or cheap to resolve....
Looks like this at the moment....
View attachment 962841