On Feb 28, 6:35*pm, Charlie Papa wrote:
I have a Discus 2cT with about 650 hours on it. *Schempp-Hirth did the
instrument installation, and a more professional looking job you will
not find. *But there was one problem that confounded even the avionics
guy: when the engine was running, pressing the push-to-talk button
would kill the engine until the button was released.

The engine's ignition is a very simple magneto (Solo 2350), and the
radio a Dittel FSG2T radio, - yes, the one with a recall. *How to
explain the ability of the radio to ground the magneto?? *No one even
had a theory. *But when I reinstalled the radio after the recall
service (which was very efficiently and courteously handled by Dittel,
BTW), the problem was gone. *I tried to induce the problem several
different days, but it exists no more.

So what flaw in this radio can cause such an effect? *A black curse?

It's a fun mystery - one not unheard of with piston airplanes. It's
usually indicated by short, sharp "Yikes!" or "Oh S----" transmitted
on the tower frequency as the engine quits when the PTT button is
depressed.

Seriously, assuming the Solo magneto works like Bendix or Slick
airplane magnetos, shutting it down requires grounding a field wire.
I would disconnect the ground wire at the magneto and measure the
wires resistance to ground with the PTT on and off. If the wire goes
to ground when the PTT is pushed, keep measuring sections of the wire
until you isolate the problem. My top suspect is the magneto switch
in the panel with worn-through wire insulation as a close second.

Hypothesizing, EMF may be moving the wire or internal switch parts to
ground as the PTT switch is pressed.