thanks Elizabeth, hoping they'll stand behind their product. I'll report back my experience in resolving this issue. Pretty inconvenient packing up a heavy amp and even worse.... no music for awhile.
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Dave & Andrew, thanks for your replies. Considering it’s happened twice, I’m going “by the book” on this. Boxed it up and returned to the dealer. Microprocessors are way outside my wheelhouse. The manual recommends holding down the power button and allowing the amp to cycle. This did not work so I’m reluctant to attempt a fix that McIntosh or the dealer does recognize. (no offense). If I discover the way to do a (McIntosh sanctioned) firmware update to correct the problem, I’ll post it on the forum. Guessing others may have experienced this issue.
I'm back in business. Turned out to be an issue with the firmware again. Pretty simple fix... un-bricked the 7900 by shorting (depressing) the TST which is a (labeled) button on the circuit board, plugging it in for 15 seconds (while holding down the button) then unplugging it. Once the unit was put back together, AC power was applied (just the LED light was lit/ no display) and a USB cable connected between a PC and the 7900 was used to upload the firmware update. After the firmware loaded.... viola ! This was performed by a trained McIntosh technician, however I think anyone who has basic skills and can follow directions could do this for themselves. Not sure if McIntosh will provide firmware updates (via email/drop box) to consumers.... I certainly hope so as it's not a difficult procedure and re-boxing a 75 lb. amp and hauling to the dealer is not too convenient.
I would like to know if anyone has opinions on what might be the cause of the firmware issue and whether or not a power conditioner would help to address any power fluctuations that may cause this ?