MA6200 buzzing in left channel

[strymeow]

Greetings, McIntosh crew. I woke up on Friday, turned on my MA6200 like every day, and got some buzzing/humming in the left channel, which as I troubleshooted I was able to replicate across all three speaker-pair terminals. The volume of the buzz/hum stays constant regardless of volume, and it does not switch channels when I turn the Mode Selector knob to reverse. I also noticed some faint crackling in the left channel when I played some music, at which point I turned the unit off. The buzz/hum did increase in intensity & volume when I activated a second pair of speakers (i.e., the speakers were connected to terminal 1, and when I activated terminal 3, the speakers on terminal 1 exhibited increased buzz/hum).

This unit was last serviced by Audio Classics in 2017. Any thoughts on what the current issue might be? And any recommendations for repair tech in the central MA area? Closest certified McIntosh shop is near Hartford. Would like to avoid that drive, and don't want to mail it off if I can avoid it.

Thanks for reading.

 

[clinic-audio]

hello strymeow

on every input ?
on both channels ?

 

[strymeow]

Yes, on every input. Only in the left channel--see my post for details. Thanks!

 

[Bob the Tech]

The mode switch is early in the signal path, Can you pull the jumpers from the rear and feed the preamp outputs to another amp, or feed another (volume controlled) source into the power amp inputs and try to determine if the noise stays with the preamp or the power amp? This would help isolate the preamp from the power amp.

 

[strymeow]

Hi, Bob. Thanks for your Q. I removed the jumpers between preamp & amp, and the hum/buzz remained as before, and again increased in intensity when I activated more than one speaker pair. This would suggest that the problem is in the amp section, correct? Thanks again.

 

[Bob the Tech]

Yeah if it’s buzzing with nothing connected it’s in the driver or amp. If you’re motivated you could go in and swap the driver boards left to right to further isolate driver vs. heatsink.