B&K Reference 3220 amplifier--one channel not working

[christ1]

I have a B&K Reference 3220 amplifier (that I purchased from the Garage Sale) and one of the channels is not functioning. There is some sound coming from the channel but it is very low. I have done the usual troubleshooting to isolate the problem to the amp. The volume dial on the back of the amp does change the volume. It seems like the amp is not actually amplifiying the signal.

Looking at the manual it lists seemingly this problem and says a blown rail fuse as the possible cause. There are 3 pairs of glass fuses (2 pairs on the left vertically orientated boards and a pair on the right vertically oriented board). Are these the rail fuses for the 3 channels? I have popped them all out and there is nothing obviously wrong--they all look the same (2 of the channels function correctly). Though I have not yet checked with a multimeter to confirm an open or closed circuit through the fuses.

Are there any other causes it could be that would be simple to fix? Any help would be appreciated.

Thanks.

Edited May 16, 2014 by christ1

[willland]

I had a B&K Reference 4430 and it had a very similar problem, very low volume on center channel even when gain knob on back was at max.

I took it to my repair guy and he replaced the mosfet output transistors for that channel and set the bias to factory spec and it was as good as new. I am not saying that is definitely your problem but it sure sounds familiar.

Bill

[christ1]

I had a B&K Reference 4430 and it had a very similar problem, very low volume on center channel even when gain knob on back was at max.

I took it to my repair guy and he replaced the mosfet output transistors for that channel and set the bias to factory spec and it was as good as new. I am not saying that is definitely your problem but it sure sounds familiar.

Bill

How much did that cost to fix?

[Youthman]

Try swapping fuses to see if fuse is the problem

[christ1]

Good idea. Is there directionality to the fuses, i.e. current should flow in one direct but not the other? They have a purple band on one side and the wire in the fuse is asymmetric--one side is coiled like a spring.

Edited May 16, 2014 by christ1

[willland]

Posted 16 May 2014 - 05:07 PM willland, on 16 May 2014 - 5:01 PM, said: I had a B&K Reference 4430 and it had a very similar problem, very low volume on center channel even when gain knob on back was at max. I took it to my repair guy and he replaced the mosfet output transistors for that channel and set the bias to factory spec and it was as good as new. I am not saying that is definitely your problem but it sure sounds familiar. Bill How much did that cost to fix?

I think I paid around $90.00 out the door, but that was four years ago.

Try swapping fuses to see if fuse is the problem

Good advice Michael.

Bill

[Youthman]

Fuses typically can go either way

[CECAA850]

Just check them with a meter while they're out. One could be blown on the end where you can't see it.

[derrickdj1]

I think I paid around $90.00 out the door, but that was four years ago.

I wish some of the repair work up this way was that cheap!

[christ1]

Try swapping fuses to see if fuse is the problem

I swapped fuses and generally poked around inside. It was not the fuses but when I tested it all the channels magically worked. I am guessing there is a loose wire or other connection somewhere which I "fixed" when I was poking and prodding the wires. Hopefully it stays working. Thanks.