Thats pretty cool, and pretty much why I had been thinking of designing an isolation circuit for the PMD.
It could be BS, but they claim the lack of grounding on the sink surface and those thermal pads was causing issues. However the person says that you cannot ground the sink because the transistors collectors' are electrically connected. the transistor collector is tied to its case, but I have to believe its electrically separated from the sink. It doesnt make sense to push the power for the fuel solenoid through the entire sink, especially when it doesnt say anything about risks to placing the PMD on metal.
I just checked the spare PMD I have and it the transistors are isolated from the sink. The annodized coating does prevent electical continuity for the most part, but in the screw holes it is not perfect and there is some electrical continuity from screw hole to screw hole. I scratched off some of the annodized coating and still couldnt get continuity to the transistor. It could be that they were concerned about the internal isolation of the transistors failing and didnt want the fuel solenoid power going straight to ground, which would kill the PMD outright. I would be more interested to see an entire schematic of the PMD to see if anything else is tied to the sink.
Perhaps the best mousetrap is yet to be built.
