The system runs O.K. with the Tuner removed from the bus. It is not possible (easily) to run the Tuner seperately since it is both controlled and powered from the Quadbus. There are individual on / off buttons on the Tuner, CD player and preamp but they all turn the whole system on and off, it is not pssible to power units seperately while they are on the Quadbus. The problem occurs between 20 minutes and 5 hours after switch on depending on ambient temperature but I have been unable to recreate it with the top off the Tuner so that I can poke around looking for clues. In my experience heating and cooling this type of fault is often highly misleading and I am reluctant to return the unit to Quad since it is likely to result in a "no fault found" report and a bill for £££.
This is why I was hoping someone might have previous experience or knowledge of Quadbus systms.
Barry