Nope. Never resolved.
I think the answer lies in a mosfet blowing. But without the schematics it is very difficult to tell. I've tested all the resistors and fuses on the boards that I have and they all seem to be conductive, although of course without schematics I cannot tell whether there are any that are partially failed and therefore at the wrong value.
If anyone has copies of the schematics online I can test further.