I had a solder connection failure on the unit as Mike did not
use spacers and long screws to mount it on the instrument
panel. He used only the front plastic panel.
Fortunately I caught this before I flew the RV4 again.
Mike had about 50 hours ground running and flying.

In some cases the flat head 6-32 screws will wind up partially
under the knobs and perhaps under the switch lock washers.

The reason it probably failed is the cantilevered weight of
the harness and DB15 connector off the back side of the unit.
That puts a strain on all the solder connections.

I am in the process  redesigning the PCM to make it much smaller
and to fix this problem in the bargain. If you have a PCM
mounted only by the plastic PCM front panel I suggest adding
these spacers and long 6-32 screws to better support the PC
board.

Paul Lamar

Be careful- I put four nylon screws with nylon nuts  through the circuit
board where you indicated, and through the faceplate. When I tightened
them up (and gently, no less) to take the stress off of the solder
connections, it put a little too much pressure on the solder connections
where the mixture pot solders to the circuit board. Consequently, I had
an intermittent missing problem when I would put any pressure on the
mixture pot while running. It is now fixed, but it is a possible issue.
I've always thought that the PCM panel should be enclosed in a case so
that there isn't any stresses on the circuit board. Whatever can go
wrong, will go wrong. The solder connections are taking the entire
stress that the wire harness might be putting on the connector.

So, you've got the plane flying now, Paul? What do you think of it?


Brian Trubee


Close but not quite flying. I am still working on mounting
the new PCM.

I had to make  new spacers from aluminum tubing for the PCM.

Paul Lamar