I have a XTi1002 with ch2 not working, actually the amp dosn't complete the power up cycle.
It starts up puts CROWN on the display for 5 ish seconds then fires the crowbar and shuts down.
Things I've done so far:-
Removed both OP device heatsinks with devices attached, they all meter as good.
Removed both driver transistors Q132 & Q133 which have exploded.
Removed pre drivers Q129 & Q131 these meter OK, although I do have replacements.
Removed R225 & R226 340ohmRs as they are both open circuit.
Removed D189,D188,D187 & D190 as they are all short. Metered between collector connections of Q132 & Q133 and the 100ohm resistor R258 looks good.
Checked Zeners D160,D151,D158 & D150 with a 20vPSU, a 1K resistor as a load and a multimeter and they all correctly reverse bias at 16v, checked D155 & D153 while I was at it and there ok.
Metered the paralleled emitter resistors of the OP devices, all appear ok at 0.47 Ohms.
Checked all the other transistors of ch2 on the board and they all appear at least with two good junctions.
The amp now correctly powers up, all be it no ch2, but my question are:-
1. Should there be anything else I should check before putting new drivers Q132 & Q133, new pre drivers Q129 & Q131, new R225 & R226 340ohmRs, new D189,D188,D187 & D190 bias diodes?
2. Why did the drivers explode in the first place