A little unfair there - there's a long way to go before this works again, and I'm carrying cost and risk in repairing it - for some the downtime wouldn't warrant the cost of replacing with new. Also, to be absolutely honest, I don't think it's cost-effective for me to have spent trying to clear some form of metal debris from the fan supply solder pads for the last hour (finally resolved with a 0.4mm drill - which I managed to snap in the hole) - it was clear on inspection that the fan wiring was a bodge job with the assembler unable to poke the wire through the hole - silicone hides a whole multitude of sins on PCB assembly in china.

If it wasn't for this damned lock-down I'd throw the controller in the bin and be done with it, but being forced to spend time either with the wife or with a soldering iron, there's some curiosity value for trying to repair. But I do have some rather expensive tools to support that curiosity. Also for many in this game there's a lifetime of experience of feed rates and chip loadings that I just don't claim to understand, but then I wouldn't expect them to understand the behaviour of a h-bridge and failure modes of a MOSFET.

Horses for courses.

(but I'm determined now to get this sucker working again)