Removed and disassembled controller. See details at Motor controller disassembly, Gem e2, T6.
The good news is that I think I have finally found the problem.
One of the MOSFETs has clearly exploded. It has jettisoned two of its legs (still to be found), taken out a bit of circuit board, left sooty deposits over a significant part of the PCB and left its mark on the inside of the plastic case.
This discovery vindicates the decision to risk opening up the motor controller.
Aside from that the news is clearly bad.
I still need to use some solvent to clear away the sooty deposits, but the presence of surface mount components suggests to me that there were copper tracks on that side of the board. I suspect these are long gone in the proximity of the explosion and it remains to be seen if I can work out how to re-instate them.
I can see the markings on other MOSFETs.
These markings differ only in the bottom row which I am hoping is a batch number.
At this stage, speculation might be moot as there is probably only one way this is going to go, but we’ve come this far so I will press on in the next post.
In the meantime here are some more pictures of the carnage.
