One possible clue, I thought in the steam PS2 upgrade wiring harness system, we have PV generated by 2 diodes on the tether socket PCB. Smoke heater and headlight I believe both use that PV source.
The key there is again, the way that works, there are 2 diodes that use the motor leads (white and yellow) to create PV that is on the purple wire to the smoke unit. Let's say you made a mistake and somehow while servicing the smoke unit, one of the resistors touches the housing that then is mounted to the frame- effectively frame ground AC.
It is highly suspect you may have pinched a wire or moved one of the resistors or some other failure that might inject AC from the frame or shell the smoke unit is mounted to back into the PV line and thus back into the motor. This would be extremely bad and could damage the PS3 board. Again, being you just worked on the smoke unit- that is the first suspect.
Again, you must make sure that no wire going to something like the smoke unit or any light, the couplers, the motor and so on- none of those ever can be shorted to frame.
The only wires that can touch frame are the black power wires in the harness system specifically meant to attach to frame.