WOW Mark, I am impressed! That helps a lot! It seems to be exactly the same as mine except on mine the current transformer coil is not on-board and there is a connector for it. I will study that page carefully and, indeed, the rest of your site. Thanks so much! I wish I had found it sooner.
BTW, these units with current transformer coils are supposed to go up to something like 100 A but they sell pretty much the same device with straight current measuring and they are supposed to go up to something like 10 or 20 Amps.
In your schematic the current sensing resistor is 0.68 ohm but I measured mine at something like 0.1. While the design could be different I am thinking it is also possible the value increased over time. I have found several instances in past repairs where SMD resistors had changed value or blown, probably because they were dissipating more than they could. It does not seem to be the case here with the 0.68 ohm resistor though. I will have to measure and compare the values of all components on the back board.
With your schematic I can proceed with testing much more. I was not quite prepared to spend the time to reverse engineer the thing. I have reverse engineered quite a few things, mainly SMPS, and it takes me many hours. Too much work.
Thanks again for that valuable info. I will keep this thread updated as I make progress.