OK, in your previous post you mentioned IB, OB, and KReg being 0V. This is on the larger C4S board, not the smaller one (it doesn't have a Kreg).
IB on the larger PC board wires into the high voltage power supply at 34U, and you need to do a DC voltage check of 34U. If it's 0V that is significant. If it's more like 380V and IB is 0V, then they are not connected.
