The reason I worded the posting in that fashion is because "if" what was suggested did not make any difference then an internal "detailed" investigation has to be made from the power supply backwards to find the reason for the tripping out. The problem can be anywhere, maybe even the power unit itself at fault! or possibly the amplifier IC partially shorting out causing excessive power to be drawn from the supply (this causing it to cut out) or a secondary component at fault, usually (but not exclusively) a capacitor. Its really a case of a methodical procedure that has to be gone through to isolate the problem and which really requires diagnosing by a suitably equipped engineer armed with the service sheet. It should be appreciated that at least 90% of modern day equipment failures requires bench repairs to make whatever serviceable again.