Looking for some quick help with a blown amp!

[CarnahanBB]

Hey folks! I'm considering the purchase of a pair of B&K M200 monoblock amplifiers. One of the amps had it speaker outputs shorted (positive speaker wire touched negative speaker wire) according to the current owner. He says the rail fuse blew and he replaced it a couple times and it continued to blow (duh!). In any case, my question is can this be repaired? I'm not sure what output devices are used in the M200 and whether or not they are still available? Will the sound of the amplifier be altered by this repair? Any and all help is greatly appreciated as time is of the essence.

 

[ryuuoh]

Just about anything is repairable, the question is if you have documents and the proper parts. I hear B&K are a bit anal about their service manuals.
A repair and alignment shouldn't change the sound for the worse.

 

[sfox52]

I think B&K have been out of business for a while, though service info must still be around. Let us know how it works out, that would be a nice set of amps!

 

[CarnahanBB]

Thanks guys. I just didn't want to put my self in a situation with unobtanium parts. The tech I've taken all my gear to just always seems to fix things and never mentions repair manuals or anything. I've always wanted M200s so I may take the plunge I just want to make sure they'll be in tip top shape after repair.

 

[RossW]

According to my research they should be 2SK504 and 2SJ115 outputs. Out of production so you'll probably be stuck replacing all of them with a substitute part or risking counterfeit parts on ebay.

 

[CarnahanBB]

Ross, thanks so much! That's what I was looking for...Damn how did you figure that out?

 

[CarnahanBB]

Follow-up question: If you short an amp by touching the - and + speaker wires is it a sure thing that you are going to blow the output transistors if the rail fuse blows? If you replace the fuse and try again...and again I'm guessing the likelihood is only increasing?

 

[cdfac]

what probably happened is that the output blew to a short, which then blew the rail fuse. replacing the fuse isn't going to help because the shorted transistor is still there. a quick check once you have the amp would be to pull all of the output transistors and then check whether a new fuse still blows. you can then test the transistors for shorts with a DMM (not sure which leads to look at for this MOSFET). this wouldn't necessarily narrow down the problem completely as there could be further problems upstream, but it's a start.

 

[CarnahanBB]

Thanks cdfac! I'm not 100% sure if I want to pull the trigger on these amps anyway. I've always wanted M200s because I really like the other B&K amps I've had but I don't want to end up with two amps that sound different or have different parts.