Denon POA-2200 blew again

So one channel was blown, all four outputs. I replaced them, and it seemed to be working. First time I powered up with the DBT, then without when I thought it was good. Bias was reasonably close, I hadn't touched the pot. I'm letting it bias, and it blows again, taking two of the outputs. I'm replacing those outputs again, and putting in a new bias trimmer.

What else could have caused it to blow again? What can I do to ensure this won't happen again?

to prevent it again? go back to the power supply.

for interested the manual is here. http://www.hifiengine.com/manual_library/denon/poa-2200.shtml

Gave the manual a quickee and if you isolate the ps from the rest of it.. couple rectifiers there and quite a few components to check.. i'd check the same without another power up.

Ya know? wonder why a fuse didn't go? check the manual for fusistors, fuse type resistors, too. Only looked at a few denon schematics and yours is a little confusing as these were av's but denon used them like sony did, too. thing is they didn't usually fail but lost their resistance.. alas.

Binkman said:

to prevent it again? go back to the power supply.

for interested the manual is here. http://www.hifiengine.com/manual_library/denon/poa-2200.shtml

Gave the manual a quickee and if you isolate the ps from the rest of it.. couple rectifiers there and quite a few components to check.. i'd check the same without another power up.

Ya know? wonder why a fuse didn't go? check the manual for fusistors, fuse type resistors, too. Only looked at a few denon schematics and yours is a little confusing as these were av's but denon used them like sony did, too. thing is they didn't usually fail but lost their resistance.. alas.

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Fuses did go. Took the 8A rail fuses.

A power supply problem wouldn't blow the amp would it? Normally the supply voltage would just collapse if the supply blew.

Bogus replacement xistors?

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change the drivers and bias transistors and check all resistors and solder joints .

Pio1980 said:

Bogus replacement xistors?

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Nope. Sankens from Digikey, same number as original.

petehall347 said:

change the drivers and bias transistors and check all resistors and solder joints .

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Solder is good. I can change the drivers out with a pair from the the good channel of the last one of these I fixed.
when I first fixed it I changed one of the low resistance resistors. The others look fine. Emitter resistors tested good. In my experience the 1/4 watt ones normally show it visually when they are hurt.

I changed the bias pot, bias transistor, drivers, and touched a couple more solder joints. It played on the DBT for 30min with no issue, and me keeping a very close eye on it. Dare I plug it into the wall and do a power test?

Raccoon1400 said:

Dare I plug it into the wall and do a power test?

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Yes, I dare.

It passed a power test to full power yesterday, hoping it is good now.

Make sure you check traces when you have a tough one like this. I had a recent unit that kept blowing output trannies and main fuses. Checked every component THREE times on all 7 channels and every one was perfect. When eyeballing them with a loupe, I saw a weird reflection off a trace and went in for a closer look. Sure enough, there were tiny little cracks in a few traces (no doubt a drop victim). Bridged the cracks with a few jumpers, and I was back in business. Stands to reason: if the design is good (and why wouldn't it be) and all the components check out, the problem HAS to be the connections between components. We always check solder joints, but rarely look at traces.