Problem with Denon DRA-455

[smithy666]

I've got a friend's Denon DRA-455 receiver to look at which she said has blown her woofers twice (scan-speak 18w-8545). She said she wasn't playing it very loud (I think it is rated at 65W/ch).
I've hooked it up to an 8R load and run a 1kHz sine wave through. When I wind the volume up a bit it starts to clip at about 5V P-P - both channels are doing this. The output devices are 2SC4278/2SA1633. Collector voltages on these are around 48V and base voltage is about 0.56V (no load, no signal). The PS caps seem underrated at 56V (little room for error) and the top of one seems a little swollen. Could these failing cause it to clip at such a low level? Otherwise there is no sign of any damage to any components.

Does anyone have a schematic for this unit (or service manual) or can offer any suggestions for locating the fault.

Thanks