McIntosh MR78 Tuner In Need of Repair

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McIntosh MR78 Tuner In Need of Repair

Postby nineno » Thu Jul 19, 2012 9:54 pm

Hello DIY Tube community -
It's been awhile since I've checked in here and it looks like I've missed a lot of interesting audio (and non-audio) related conversation. I hope to catch up with many of the threads in the coming weeks.

However, I am seeking some analog hardware repair help. 3 or 4 months ago I went to use my McIntosh MR78 FM receiver for the first time in about a year. I had received a new Leaf antenna and I wanted to see if it had enough overlap with the FM spectrum to work as a good radio antenna because I don't have my aerial antenna coax cable run to where the Mac tuner sits.

I fired up the receiver and was dialing in some of the stronger FM stations in the area and everything seemed to be going fine until I lost the tuning and I smelled something foul. Something inside of the Mac let go of the magic smoke. A small trail of vile smelling smoke rose out of the chassis. After I got everything unplugged I had to leave the living room for a while to let things air out.

Eventually I popped the bottom of the chassis off. Some of the fried components were plainly visible on the very bottom of the tuner. The main failure looks like a ceramic bodied power resistor on the power supply board (McIntosh part number 044-453).

Of course, I don't know if something upstream of the PS board (filter caps, or transformer?) failed first which ruined the P/S board.

Since that initial inspection I haven't gone back to look at the tuner because I got distracted by a new job and summer house work. (Lame but true excuses...)

Does anyone here have experience repairing these tuners? Or, can you recommend someone that is expert in repairing them? I don't mind trying to fix the turner myself, but if anyone could give me some pointers to help ensure my success I would certainly appreciate it. I can always send it to an authorized dealer or back to Mac, but I expect that will be a ridiculously expensive affair.

The serial number is AD2422 which means it falls into the "early" MR78 build, I believe.

If any of you are McIntosh gurus, please drop me a line. I can provide some specific details and pictures of what's going on. I really appreciate the help, everyone.

All the best!
nineno
 
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