Thanks Paul. Yes, the 0R22 resistors don't seem right. R27 (TR10 side) is showing as 0.4 ohms, and R26 (TR9 side) is showing a negative value that changes and contradicts itself as I change measurement range on the meter. I've never seen anything like that before - could it be an effect of being in the circuit with the blown transistors?
As for the transistors, using the continuity tester mode on the multimeter I can say that:
TR7 has a closed circuit from collector to emitter in that direction only and nothing else
TR8 has a closed circuit from collector to base in that direction only and nothing else
TR9 has closed circuits between all terminals in both directions
TR10 doesn't have any closed circuits at all
So it looks like I need to take the board out, desolder some components and test and replace them as necessary.
Just out of interest, I'm curious as to the cause of all this. The amp worked flawlessly for several years, and was doing so when I last used it. It then lived on a shelf, and has suffered no physical or environmental insult that I'm aware of. When I plugged it back in to the system, I did so observing all the usual rules - I never connect or disconnect interconnects or speaker cables with the amp on, and the amp is always the first thing to be turned off, and the last thing to be turned on. When I turned it on, there was no thump, pop, crackle or magic blue smoke, and none of the components look burnt or damaged in any way. I'm not aware of solid state components expiring of old age while off. Any ideas what might have caused this?? I'm just concerned that since I've no idea, I have no confidence that replacing the components and putting the board back in won't just 'expire' a bunch more!