GEM 1200 Problem

Our Seneca has a GEM 1200 - it was installed during an avionics upgrade about 2
years ago. Up until now it has worked fine BUT .....

I'm hoping someone out there has fixed a similar problem or has some insight (no
pun intended - into what the problem might be.

Anyway, the GEM has an intermittently flaky display. Sometimes it goes crazy
and the bar graphs and digital temp readouts start fluctuating wildly. It
isn't just one engine and it isn't just one cylinder. Its all of them.

So far I've not been able to associate any particular activity with the problem
except perhaps "heat".

Observations:
- It never shows a problem on the ground, even during runups to takeoff power.
- Usually it works fine for about 20 to 30 minutes on the first flight of the
day. However, I was just in Florida where I made three flights where the OAT
was over 80F. In all three flights the gauge was fluctuating within 60s after
takeoff. But then today I departed Sanford with the OAT at 62F and it worked
fine for about 20 minutes and then sporadically for the next 5 hours..... In New
Jersey (home base) the temperature has been 40F or below since this problem
started...
- On some flights the gauge is totally unuseable. That is, the fluctuations
are continuous. On other flights the fluctuations occur sporadically at
seemingly random intervals.
- I've tried turning on/off: mags, alternators (even both), heater, fans, all
other avionics, prop ice, overhead lights, dimmers, etc,. Nothing makes a
difference or seems to affect the flucatuations. Haven't tried shutting down an
engine.
- Pulling the breaker on the GEM and resetting it doesn't seem to help. I've
left it off for an hour, in flight, turned it on and had it "go crazy"
immediately.
- On advice from a mechanic, I tried pushing on the display to see if that
would stop the "jitters". No dice.

The avionics are cooled by a fan -- but there is no cooling directly on the GEM.
It gets warm to the touch. But then its been that way for two years and
certaily it is much cooler now than on a typical summer day.

It went back to Insight. They say they bench tested it and its OK. But I
wonder how thoroughly that was done?

My personal guess is that it is heat related but there isn't really that strong
a corelation.

We've also tried relocating the wire harness thinking that it was picking
something up -- like an antenna. No noticeable difference.

The only recent work on the airplane was that we replaced the aluminum cables to
the starters with copper cables. But then, they don't carry any current in
flight. The only aluminum cable replaced that carries current all the time is
the piece from the battery to the bus -- from the bus it goes to the starter
solenoids and to the avionics bus.

The wiring harness grounds have been checked. The wiring harness has been
inspected (both sides).

Jim Kaufeld

Jim Kaufeld