Well I couldn't have asked for a cheaper or easier repair. I plugged in a patch cable between FX Send and Return and voila, good volume. I then took out the patch cable and no change. One of the jacks must have been stuck open, routing the signal away from the inboard path.
There are a couple of little things to fix on it, nut and washer on FX Return jack, new 1/4" plug for the remote switch, but for $50AUD plus $20 in fuel and tolls to pick it up it's been a great investment.

Thanks DrGonz78 for the schematic. Yes, I don't know if it is really a safety issue they are concerned about "We don't advise consumers working on our goods as they contain lethal voltages" or if they just find that a convenient excuse. Thanks for the tips on isolating the pre and power etc., I will try that tomorrow and see what I can do with the schematic at hand.
I'm not a very knowledgeable electronics person, but I can pick things up reasonably easy, have built a small tube amp etc.

I picked this up yesterday with a problem. Very low volume, what I would regards as around 1w. Marked on the chassis as August 98. I contacted the distributor here Music Link Australia, for a copy of the schematic (which is what Peavey advised) but they won't supply one to an amateur. Service technicians only. Would anyone please have a schematic for this?