Perhaps an evil spell??

[Charlie Papa]

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?

[Andy[_10_]]

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

[Grider Pirate]

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.

[jsbrake[_2_]]

> 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!

[Whiskey Delta]

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?

[Andy[_1_]]

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

[bildan]

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.

[seventripleone]

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.

[Andy[_1_]]

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

[Andy[_10_]]

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/meddelanden/TM5_Dittel_SB_FSG2T-1-061281718159.pdf

9B

[Mike the Strike]

On Mar 2, 2:02*pm, Andy > wrote:
> 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/meddelanden/TM5_Dittel_SB_FSG2T-1...
>
> 9B

Our company makes a very good living tracking down electromagnetic
compatibility issues like this. Radio frequencies impinging on
unshielded control circuits can end up being rectified and appearing
as a spurious dc signal. We've seen this a lot in electrical control
and industrial process control equipment (a few years ago I watched a
robot throwing gearboxes across a car assembly plant instead of
handing them gently to the next robot in line!). I would strongly
suspect something similar is happening here - 120 MHz is a great
frequency for the purpose.

Mike

[seventripleone]

On Mar 2, 9:05*pm, Andy > wrote:

> 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.

I'd generally fully agree with you on this one, but there is no signal
outside of the electronics box (case mostly metal and made by Ilec
BTW). Except that you can connect an external voltmeter to act as RPM
indicator on older units and on new ones there is perhaps an internal
DVM module to do the same.

The box senses the RPM as ignition pulses via the earthing lines from
the two ignition modules (coils) and does the conversion internally.
Depending on said signal three LEDs are lit to indicate in which PRM
range (green, yellow, red) the engine is turning and the ignition is
switched off (earthed) when a threshold of ~7000 RPM is exceeded.

The above does contain some informal reverse engineering concerning
the internal workings of the box on my side to be honest but i'd
happily buy you all a round if i'm wrong.

(IMHO it's much better to try to contain the RF in the radio and
antenna cable than try to harden everything in the glider against it.
Otherwise i'd end up with tinfoil around my b**** :-)

[Charlie Papa]

On Mar 4, 3:27*am, seventripleone > wrote:
> On Mar 2, 9:05*pm, Andy > wrote:
>
> > 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.
>
> I'd generally fully agree with you on this one, but there is no signal
> outside of the electronics box (case mostly metal and made by Ilec
> BTW). Except that you can connect an external voltmeter to act as RPM
> indicator on older units and on new ones there is perhaps an internal
> DVM module to do the same.
>
> The box senses the RPM as ignition pulses via the earthing lines from
> the two ignition modules (coils) and does the conversion internally.
> Depending on said signal three LEDs are lit to indicate in which PRM
> range (green, yellow, red) the engine is turning and the ignition is
> switched off (earthed) when a threshold of ~7000 RPM is exceeded.
>
> The above does contain some informal reverse engineering concerning
> the internal workings of the box on my side to be honest but i'd
> happily buy you all a round if i'm wrong.
>
> (IMHO it's much better to try to contain the RF in the radio and
> antenna cable than try to harden everything in the glider against it.
> Otherwise i'd end up with tinfoil around my b**** :-)

Thanks for the replies, - at least the reasoned and helpful ones. I
am at Seminole Lake and spent a half hour yesterday with the very well
informed TA discussing the mystery. Additional information, that may
be relevant:
• I don't know if the problem has existed from the beginning, as with
the engine running I can't hear myself think. It was only recently,
while flying with a friend, I got low and advised I was going to light
the engine. He asked me to advise him when it was running, and so
even though I knew I would not hear a reply, when it lit as it very
reliably has, I pressed the PTT and had an Oh Sh*t moment. I released
the button and the engine caught again. I again tried to transmit,
and the engine died. The following day I verified while just off tow
that each push killed the engine.
• I did not look for the effect on the LED's which might have been
showing an 'overspeed' signal
• I tried the PTT when the radio was removed for the recall, and there
was no effect
• I don't have the knowledge to trace ground leads and the like, and
so did not

TA theorized, if I can explain it accurately, that RF interference was
picked up by the wires from the rev sensor and the sensing unit
interpreted these as excess RPM, and grounded the magneto. This is
similar to the speculation from seventripleone. 711 has offered me
his unrepaired radio to try to again induce the problem, and eliminate
the possibility that it arose from frayed wires in the harness.

Me, I like the explanation that I let the smoke out. Thanks all.

Charlie Papa