Fried B&K Amp

Brasiliaflyer

So I just got a used B&K 7270 that was working fine. I had tested it briefly and left it alone on the carpet. Well, my wife noticed a strange smell coming from the basement, and I found my amp idling on. I don't know if I left it on or if the kids turned it on. The problem is that on carpet there is no airflow. The thing was HOT. So, I shut it off, and then (curiosity killed the cat) turned it back on to make sure everything was ok. As soon as I connected the cd player, there was a puff of smoke, and the red light faded away.
So, I cool it down, take the cover off, test all the caps to make sure they are dead with a multimeter, and start exploring to see what happened. I found a tell tale mark of one of the resistors overheating, and the inrush fuse is blown. I replace the fuse, and briefly turn it back on and I notice one of the caps is smoking. Shut it back down, and now I am perplexed. The caps look fine (no bulging or leaking) but there is that resistor. . . Is it possible that the resistor is causing one of the caps to act up, or am I in over my head? I could easily solder it out and find a new one to replace it, or am I screwed?
Anyone know a good amp repair shop in SLC Utah?

The first picture is the overheat mark, the second is underneath. The resistor in question is the white one behind the little green ones.

Crazy there is no thermal protection on that monster amp!

Thanks for any input!

Brasiliaflyer

Yeah, one of the big blue ones was smoking on the very top.

Brasiliaflyer

Thanks for the advice. I put it all back together and dropped it off at an electronics place who specializes in audio, and has a 5 week backlog for work. Couldn't find any authorized B&K shops anywhere

dorokusai

I'm looking at the thermal protection in your picture, it's called a fuse. The secondary thermal protection are the heat sinks and it sounds like you created the condition that blew it up. I'd send it back to Eastern Elite A/V not some generic shop. It's basically the old service department from B&K. George is the guy you want to talk to there.

FTGV

Brasiliaflyer wrote: »

Crazy there is no thermal protection on that monster amp!

The thermal protection will most likely be in the form of a thermal switch attached to each heat sink.They will activate only when the output transistors create enough heat in the heat sink to exceed the temp rating of the switch.A fault in the power supply such as with your unit would not normally be thermally protected.

Brasiliaflyer

I tried calling Elite A/V but the recording referred me to email. I sent one, but have not heard back for a week. Started wondering if they were even still in business. I'll keep trying. Problem is that shipping will be about $200 for the round trip, but considering that the local guys quoted me $500-$700 for the repair, I will see what they have to say.

shawn474

George is great to work with. They seem to lag about a week in emails, maybe 10 days. That is coming from a few experiences. Once they get to you, they are pretty helpful and accomodating.

Brasiliaflyer

Anyone have any personal experience with eeav service?