I've had 2 MTH engines do the same thing, one recently. 1st one the 5volt board was going bad. 2nd one, a 2-8-0 also a 5volt board I sent to GGG on a Monday. He indicated a short and installed the PS3-2 board. I had it back on Sunday. Amazing fast work, both have the new boards installed with no problems. GGG also returned the BCR I had installed. I highly recommend GGG for any work. 110% satisfied with his work.
What to me is amazing about these 5 volt boards how easy they go bad with no short, etc. Worked great, both the day before. Then next day after just sitting, develop problems and go bad.