Hi Red,
I seriously doubt that the "quality" of the AC has much to do with the failure of the logic circuit. It could help things along but I'd venture to guess that aging IC's and power supply caps have more to do with logic circuit failure.
I always have to wonder about the accuracy of the claims I've read about the source of machine issues. It's one thing if someone says that a problem can be traced to "such and such" a circuit because they've corrected the problem by repairing that circuit, but it's very common for folks to say that they've heard that a particular circuit is a common problem based on 2nd or 3rd hand accounts.
Now I'm not accusing you of spreading rumors but rather warning you to take this stuff with a grain of salt. If you want to learn about this particular machine, I suggest you ask someone who's corrected the issues that are being blamed on the logic circuit. Otherwise, it' just talk.
Regarding the reverse engineering of this circuit,.. anything is possible given the time and funds. The question in my mind is "would this machine be worth going to all that trouble"?
I remember when these machines were new and I have to admit that I lusted after them for a bit. I used a buddies a number of times and it was nice for a consumer machine. Later on I got a chance to use an Otari 5050 and my impression was that it was 10 times the machine that the Tandberg is.