Connecting an external PSU will temporarily disconnect its primary power supply. If it was previously powered by battery, this will be seen as a main power interruption to Vbatt. If the internal switching PSU is not stable, you'll get the effect you're seeing. I think this is the same phenomenon that Randy Kindig is experiencing on one of his units that I didn't have a chance to look at at the last Tandy ASM (sorry Randy).
So, I'm going to agree that your theory about power circuit issues is correct, but will submit that your intended fix may be insufficient. The service manual has a great section on diagnosing power circuit issues, and indicates a number of parts which may be faulty and should be checked (or, simply replaced as a diagnostic). I've also had to replace the transformer on a unit, though that one was exhibiting complete power-on failure. -Josh On Tue, Apr 2, 2019 at 2:06 PM Eric Miller <[email protected]> wrote: > > It was working fine last night. Today, the display goes blank when plugged > into power adapter. If it’s on battery power and displaying the menu, and > then I plug it in, it goes blank. If I plug it in and then turn it on, it’s > blank. Unplugging does not enable the display. I have to unplug and turn it > off and back on again. > > > Power circuit caps? > > > > -- > Eric Miller > http://pragmaticpizza.blogspot.com/ > https://github.com/eric-john-miller
