[JD From LA]

Hi Everybody,

I am ready to lose it.  I was cosmetically restoring a great sounding McIntosh MC 250 for someone.  Unfortunately, I partially disassembled the unit--and forgot to reinstall an insulating standoff on one output transistor heat sink.  When I plugged in the unit, I got a heavy hum followed by smoking from the area of that heat sink.

I either wasted the Motorola Green Label 32-070 7539 output transistor fastened to that heat sink or the smaller Motorola 023 7452.  Here's the questions:

1.  What tests can I run to figure out which is blown?
2.  Is there any hope of finding these parts?  If no, what is the best audiophile replacement?
3.  If this is not the right place for this question, could you please direct me to the right place?

Thank you in advance for any help.

Jerry

[doodlebug]

Firstly, this isn't something that hasn't been done before - I'm guilty of it in a former career myself.

I'd be on the phone tomorrow to either Audio Classics or Terry Dewick in Tennessee.  Google those names for URLs.  I think Terry may be on vacation for another week, though.

Certainly call Audio Classics and see what they can do to help.  There are replacement transistors out there for these lovely old beasts and plenty of them still operate on a daily basis.  Also, you might want to examine things closer as I suspect there's a resistor or 2 that will have gone out, too.

Cheers,

David

[audiobasics]

1.  What tests can I run to figure out which is blown?
2.  Is there any hope of finding these parts?

I have not tried it for meltdowns, but some transistors can be tested with a DMM on the diode setting.

http://www.anatekcorp.com/qdmmvom.htm

I would check with McIntosh directly. Most certainly they will still carry parts or know what the alternative is.

Good Luck and don't beat yourself up too much.