Update
I figured out a way to make the 8642B stop reporting A6 counter fault in FM mode when I go from internal to external dc. I turn on AM modulation and set it to internal then turn on FM and there is no problems switching from int to ext dc, weird. I have a A3 processor board on the way, from the troubleshooting I have done in the manual it suggests swapping out the A3 board after I already swapped out A4.
