Perhaps an evil spell??

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?

On Feb 28, 5:35*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?

Wow! I had the same repair done.

Now I am looking forward to discovering some unexpected glider
performance improvement as a result of reversing a capacitor in my
radio.

9B

On Feb 28, 6:33*pm, Andy wrote:
On Feb 28, 5:35*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?

Wow! I had the same repair done.

Now I am looking forward to discovering some unexpected glider
performance improvement as a result of reversing a capacitor in my
radio.

9B

Wow! I'm thinking a 1000 foot gain maybe.

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

Yes, Charles... those of us still in the middle of winter at your
home club have sacrificed a PW-5 to place on curse on all those who
fly in Florida while our runways are covered in snow!

On Mar 1, 11:05*am, jsbrake wrote:
So what flaw in this radio can cause such an effect? *A black curse?

Yes, Charles... *those of us still in the middle of winter at your
home club have sacrificed a PW-5 to place on curse on all those who
fly in Florida while our runways are covered in snow!

A PW-5.....? Runways still covered in snow are they?

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?

You didn't say if the glider had this problem from new or if it only
developed since the last inspection.

It would have been a lot easier to diagnose the problem if it was
still present. Did you measure to see if the radio PTT had any
affect on the mag lead while on the ground with the engine not
running? Did you measure the PTT affect on mag lead on the ground
with the engine running? If there was any affect did you repeat the
tests with the radio powered off, and then with the radio removed or
disconnected? If any of these test showed that the PTT switch was
grounding the mag lead it should have been fairly easy to work through
the wiring to find the sneak path.

The only magic that really exists in electronic/electrical systems is
how the parts are manufactured with smoke inside them. The black curse
causes the smoke to escape.

Andy

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.

On Mar 1, 2:35*am, 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?

No, the engine electronics will shut the ignition down when max. revs
for the prop are exceeded. The revs are present in the instrument as a
proportional voltage signal (1V = 1000 RPM) and i'd bet that somehow
the electronics got tricked into thinking that it was the case. A
voltage drop in the power supply from the battery during radio
transmission or an induced spike from the radio's RF power could have
been the reason.

On Mar 2, 11:25*am, seventripleone wrote:
On Mar 1, 2:35*am, 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?

No, the engine electronics will shut the ignition down when max. revs
for the prop are exceeded. The revs are present in the instrument as a
proportional voltage signal (1V = 1000 RPM) and i'd bet that somehow
the electronics got tricked into thinking that it was the case. A
voltage drop in the power supply from the battery during radio
transmission or an induced spike from the radio's RF power could have
been the reason.

Anyone that designed a system to transmit a critical parameter as a
fraction of a reference voltage but did not also provide the reference
voltage to the receiving system would be better employed flipping
burgers. In other words, a properly designed engine speed monitoring
system would be independent of the battery voltage.

RFI could have strange results though. Maybe the incorrectly
installed capacitor allowed RF on the radio power line and that
coupled into the engine monitor.

Anyone know the function of the problem radio capacitor?

Andy

On Mar 2, 12:05*pm, Andy wrote:
On Mar 2, 11:25*am, seventripleone wrote:





On Mar 1, 2:35*am, 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?

No, the engine electronics will shut the ignition down when max. revs
for the prop are exceeded. The revs are present in the instrument as a
proportional voltage signal (1V = 1000 RPM) and i'd bet that somehow
the electronics got tricked into thinking that it was the case. A
voltage drop in the power supply from the battery during radio
transmission or an induced spike from the radio's RF power could have
been the reason.

Anyone that designed a system to transmit a critical parameter as a
fraction of a reference voltage but did not also provide the reference
voltage *to the receiving system would be better employed flipping
burgers. *In other words, a properly designed engine speed monitoring
system would be independent of the battery voltage.

RFI could have strange results though. *Maybe the incorrectly
installed capacitor allowed RF on the radio power line and that
coupled into the engine monitor.

Anyone know the function of the problem radio capacitor?

Andy

I know only that the capacitor was installed incorrectly and that it
affected transmission output. Here's the link:

http://www.eaa.se/dokument/tekniska/...1281718159.pdf

9B