SX-880 in Protection

am wondering if pa3004 was damaged when q36 shorted

I was also wondering something along these lines, but I wasn’t sure if I had done an adequate enough job of ruling everything else out.

Does PA3004 have a substitute? Do I need to look for a good used one?
 
seem to remember you changed c417 and verified its polarity .
i would check the soldering then if still no use try a new pa3004 .
 
You could just lift C417 and see if the voltage at PA3004 Pin 8 comes up at all.

Also, that seems to be a LOT of AC on Pin 7. Are the two resistors in the divider (R403/404) intact?
 
Also, that seems to be a LOT of AC on Pin 7. Are the two resistors in the divider (R403/404) intact?

R403 and R404 both measure .5M ohm in circuit. 1M ohm - Brown, Black, Green, Gold.

Maybe I need to lift one leg to get a proper reading?
 
And did you pull C417? That will, of course, eliminate any timing delay of the protection circuit, so be sure the volume is at minimum and/or there is no signal present - Or disconnect the speakers.
 
Finally getting back around to this project. I’ve been looking for a PA3004 replacement, but so far no luck.

I went ahead and pulled Q35: PA3004 today and found this installed. Is this part equivalent to PA3004? I was expecting it to say PA3004 not HA1457. I think HA1457 is an opamp, isn’t it?

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Different animal, in the same skin.
HA1457 is a high voltage low noise pre-amp.
I bought a few PA3004 on ebay to try out, I will let you know if that source is legit or not when they arrive.
Make reference to where that HA1457 part is used, assembly #,reference designator, you might have pulled the wrong part.
I have used the Hitachi HA12002, it is Hitachi's version of a speaker protector IC
 
Yes I did find the other two that are supposed to be in the unit, but why is HA1457 also installed at Q35? Someone must have installed this by mistake during an earlier repair attempt? Am I correct in thinking that HA1457 is not going to work at Q35, and that this is what’s causing my protection issues?
 
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yes looks like you found the issue ..i wonder how it managed to work at all . :idea:

It never did for me. I can only assume it was a failed repair attempt by someone before me.

Geez, first wrong sized emitter resistors in one of the power amp boards of my SX-980, and now this! I guess I should have verified what was installed at Q35 as a first step.

Should I try one of the eBay PA3004 ICs?
 
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