Yesterday I instrumented the glider 12V power bus with a digital
voltmeter (DVM) so I could independently measure bus voltage if I
experienced another intermittant CAI-302 shutdown. Of couse, the 302
worked perfectly the entire 5-hour flight and its voltage reading
matched the DVM the entire time.

However, upon landing I ran across some minor ruts on the rollout,
experiencing some fairly sharp bumps. When I stopped, I noticed the
302 had turned off. When I turned it back ON, its voltage reading was
7.7V while the glider 12V power bus stayed at 12.5V.

Today I had the glider out of the box to inspect the power & signal
wiring.

Attempting to replicate the 'sharp bumps' from the previous day's
landing roll, I smartly rapped the 302 with my knuckles on the left
side of the unit, and it instantly shut down - yikes! However, I was
only able to do this once.

Nothing was obviously loose, but I removed and re-seated the 10-pin
power connector anyway.

One last thing. After reading the manual, and seeing another poster
say the factory had recommended he change the power input from pin 2
(switched power via front panel button) to pin 1 (powered directly
from glider bus), I switched my setup from pin 1 to pin 2.

So, the only things I know for sure at this point is that the low
voltage readings displayed by the CAI-302 are NOT due to low glider
battery voltage, that there is no obvious external wiring issue, and
that rapping the unit smartly is not recommended ;-).

Anyone have additional suggestions/thoughts?

TIA,

Frank (TA)

Frank wrote:

> So, the only things I know for sure at this point is that the low
> voltage readings displayed by the CAI-302 are NOT due to low glider
> battery voltage, that there is no obvious external wiring issue, and
> that rapping the unit smartly is not recommended ;-).
>
> Anyone have additional suggestions/thoughts?

My 302 would sometimes lose the vario tone to the remote speaker while I
was flying. On the ground, tweaking the 10 pin connector gently would
restore it, though it sometimes restored itself before landing.
Cambridge checked it, couldn't find anything wrong, but resoldered
joints near the input connector anyway, and sent me a new connector for
the glider wiring just in case that was the problem. I put in the new
connector. I still don't know what was wrong, but no problems since then.

So, I suggest you replace the connector. It's easy and cheap. If you
still have problems, it probably means sending it in for repair.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

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

In article > ContestID67 > writes:
>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.

Actually, a high resistance in the power lead to equipment reduces
the current, and is unlikely to result in smoke -- the current is already
limited by the needs of the 302, and further limited by any resistance
in the line. It is not impossible (the resistance may be in a small wire
with poor thermal conductivity, and concentrated hot spot), but it would
seem less likely.

Another possibily that would seem worth considering is that the ground
path is good. If it is through the mechanical mounting to the panel, and
the panel is painted, there might be a poor ground connection causing the
voltage drop in the return path. This can be extra nasty if there are
connections to other equipment that are connected to the grounded case
of the 302, causing ground current out other wires not intended for it,
or causing ground voltage to rise on connections to other equipment.

Alan