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MC7205 - Power guard lights on, right front & rear channels silent - help!?

MJF

MJF

New Member
I have a McIntosh MC7205. Occasionally over the past few years, I would have an issue where the power guard lights would come on and I would get no sound out of the right front and rear channels. When that happened, I would power cycle the amp and it would immediately clear. A couple of times it wouldn't quickly clear but then eventually would. Whenever this happened in the past, each time I was watching a movie, so the amp was not driven hard and it was in the middle of working fine; never from the start and never during loud volumes. Today, the amp had been off for several months and when I went to turn it on, the right front and rear power guard lights stayed lit after the amp went through the start-up phase. Does anyone have any experience with this? Keep in mind, this has never happened when the amp was driven hard and before you ask, it's in a well ventilated climate controlled space as well. Any suggestions, or experiences would be most helpful. Thanks in advance.
 
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The PG lights come on when a internal comparison circuit "sees" that the amp channel indicated is exceeding a predetermined distortion level.

If a catastrophic failure happens it will try to cut the input to a level low enough to not damage your speakers.

That us why we test them into a test load box to protect speakers from damage.

It needs to go to a tech for a proper evaluation and repair.

As for what failed impossible but to guess which makes no sense without bench test results.
 
Thanks for the insight on the PG. I was thinking that there maybe an outside chance for simple fix to avoid taking it in for evaluation; probably not in this instance. I was also curious if anyone else rant into this same problem with a similar McIntosh amp. My hope now is that it doesn't correct itself prior to dropping off with the tech.
 
I have the same amp and so far have not experienced any problems with the power guard. Since the right front and rear terminals on the rear are next to each other, have you checked to see if anything might be touching between them? How about inside?
 
Duane said:
I have the same amp and so far have not experienced any problems with the power guard. Since the right front and rear terminals on the rear are next to each other, have you checked to see if anything might be touching between them? How about inside?
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Good advice. The PG lamps on these later model amplifiers also indicate a fault of some kind - the OP's dilemma would point to a shorted channel. So, yes - do check speaker wiring at both the amp and the speakers themselves. If you don't find anything, then disconnect the speaker wiring from the respective channels if the amp to see if the fault remains.
 
Thanks for the advise, I thought about the same thing. The PG fault is there without the speakers or source connected. The speaker terminals as well as the RCA inputs on the back are all clear and nothing appears to be shorting out. I have had the top off and have looked over the inside closely, just from a close visual inspection with flashlight, nothing appears to be loose, or burnt from a possible fault. All the solder joints "appear" to be good.
 
I live in the Indianapolis area, there is one authorized McIntosh repair center and there's another that used to be and for some reason isn't any more, however, I've had my MX121 there under warranty a few years ago
and they did a good job fixing it.
 
MJF said:
I live in the Indianapolis area, there is one authorized McIntosh repair center and there's another that used to be and for some reason isn't any more, however, I've had my MX121 there under warranty a few years ago
and they did a good job fixing it.
Click to expand...
Hi, my MC2705 amplifier currently experiences the random going Protection mode occasional on the Right Front and Right Rear channel. Some days it works fine even at very loud volume, some days it immediately goes into Protection mode as soon as powered up. How did you fix your amp's problem? Thanks
 
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