I did a lot of surfing in search of an answer and experimenting. In my case it wasn't:
the power cord
the power supply
the latching transistor (Q4 I think)
It was just the mainboard battery CR1220!
The battery holder is both tenacious and fragile. So be careful when removing the battery. Prying it up from just below the battery while putting some outward pressure on two of the four "clips" should do the trick.
BTW. There are two knurled knobs on the back of the unit that hold in the mainboard which slides out.
After replacing the battery, the unit powered up with no problems. It must be a required input to the power-up sequence. Live and learn.
