More on intermittent CAI-302 shutdown

Frank,

Intermittents can be FRUSTRATING! From your symptoms it would appear
that something is giving you a high resistance path from your battery
to your 302. This *CAN* be a dangerous thing because high resistance
can mean high wattage which leads to high temperatures and smoke. You
don't report any smoke or "hot smells" so this seems unlikely in your
case.

Your "smart rap" on the case of the 302 points away from things like
battery, battery connections, master power switch/fuse and the wiring
between these items (watch out for wiring strung like a banjo between
two points). So what is left?

1) 10 Position Connector at the 302 - Everyone always suspects
connectors so lets look at this first. Generally speaking this type
of connector (what is it's proper name?) is a pretty robust animal.
As long as the original wiring connections were properly made in the
first place then I doubt that it would give up the ghost.

Does the voltage reading on the 302 change (or the unit power off) if
you hold the case and connector of the 302 steady and wiggling the
wires leading into it? The connections are made by tightening small
screws. Unscrew each one and check each connection and wire. There
are many strands to each wire - are they all in their proper place? I
strongly suggest that the strands be twisted together and then
soldering ("tinned") into a single "wire". That gives something solid
for the screw to bite into.

Try wiggling the connector while holding everything else steady. If
you get voltage fluctuations, this points to a bad connector, either
the female connector on the wiring or the male connector on the 302.

A rare problem is the wire breaking INSIDE the insulator somewhere
along the wire's length. The two ends of the wire are intermittently
touching and arcing inside the insulation. You find this by wiggling
the wire at many places along its length. I have seen that last one
and it can be a real problem to locate.

2) Pin 2 1 Change - This bypasses some of the circuitry in the 302
and might make a difference if there is an issue inside the 302.
Pretty simple to do and it can't hurt to try.

3) Interior Problem with the 302 - Unfortunately, if the above fails,
this is the most likely candidate for a cause. The internal
connections between the 10 pin connector and 302 circuitry may have
broken or come loose. Having never seen inside a 302 (heaven forbid!)
I don't know how likely this is. If you get to this point, then you
need to send the unit in for repair.

My $0.02. For some more general rules on avionics wiring see
http://derosaweb.net/aviation/presentations.

Good Luck,
John DeRosa