akai tx700 system amp fault

[andy9466]

ihave a akai tx700 system with a ax700 amp/tape deck. the problem is when i put power to it you can hear a relay tick then when i turn it on it lights up for around 7 seconds then shuts down! and will not turn back on again unless i remove the mains plug. then it does the same again.
i bought another one of these today from a second hand shop and coupled it to my speakers, worked fine for five minutes and has done exactly the same as the first one.
so have now found a speaker fault!
can anyone advise me on what i could have blown on the amp, i am quite experienced in delicate soldering and am willing to undertake the repair myself as there is no one near me that does repairs.
any advise welcome
andy

[andy9466]

managed to get wiring diagram and schematics but still dont know what to look for.
any ideas welcome

[andy9466]

now sorted

put two new amp chips in

andy