The buzzing is from the H-bridge that powers the IGBT’s. Half of the
fets are not getting a gate signal. The driver is not getting one of
it’s two gate signals. So I spent alot of time trying to buzz out the
board to find the pwm source for the H-bridge but could not. Anyone?

I’m glad I have a functional board now for reference. I can complete
my test fixture in minute detail. I’d like to duplicate the truck on
my bench so I can more completely test and characterize the board.
I’ve learned from rebuilding motor controls that just because
something spins a motor does not ensure that the various voltages and
pwm signals are at their nominal values. I’ve seen that a few times.
So I have a list of “test points” on my customers hardware that I go
thru and make sure are meeting spec. This took some time to figure
out. Our Dolphin boards need the same thing. I noticed that the pwm
firing the 300v supply chopper fet was 12v on one board and 10v on
another. Something is up. The board functions fine, but it strikes me
as trouble waiting to happen. A detailed test fixture makes looking at
these things much more thorough, accurate and repeatable, because
sometimes the tech gets tired 😉

Now where’s my celebration beer?