@mitch2 your last bullet point is very relevant. We have amplifiers in use by customers that are now at their oldest over 40 and at their youngest nearing 30 years of age. We have seen similar issues with an input circuit board that over the years either through misuse, exposure to heat (poor ventilation) or aging is no longer useful or completely gives up the ghost. Unfortunately we sold out of replacements a couple years ago and made a difficult decision not to produce them any longer. It is interesting to note that these days many of the repair requests we receive come from people who have tried to modify or upgrade the amp themselves or through a third party with not so good results, or bought a modified unit unknowingly that was butchered. Unfortunately the cost to repair what was done and return the amp to original spec outweighs the value of the amp itself. There is something to be said for leaving well enough alone and trust that the designer of the unit knew what they were doing.
Don’t buy used McCormack DNA 1990s amps
This is a public service announcement. There are some yahoos on other sites selling 1990s McCormack DNA amps, sometimes at ridiculous prices. While they’re great amps, and I happily owned a DNA 0.5 RevA for 20 years, they’re all gonna fatally fail. Why? Because their input board is at the end of its useful life, and when it fails your amp is dead and not repairable by anyone — not even SMcAudio. It’s a boat anchor. The only option is to sell it for scraps or get an SMcAudio upgrade that’ll cost around $2000. Given my love of my amp I chose to do full upgrades given what else I could’ve gotten for the same same price and just got it back and will forward thoughts if anyone cares. But the purpose of this post is to warn off any prospective buyers of a circa 1990s DNA amp that it’ll fatally fail soon, so unless you get a great price and plan on doing the SMcAudio upgrades just avoid these amps on the used market. You’ve been warned.