Microair M760 Intermittentent Transmit

No luck with the new wiring. And no
luck finding the service bulletin.

Microair removed all the SBs from public access. I think that
happened when ownership changed but not sure of that.

I have several of the SB, including this one, on file and can send you
if you pm me.

Andy

Thanks, Andy, but I'm not sure that will be necessary.

Microair sent me the applicable SB *and* put me in contact with the Rick at
Microairusa.com.

When I bought my glider it had a rather delicate master switch and, since
then, I've added a transponder. I'm wondering if the switch can not handle
the extra current of the transponder and/or is slowly increasing in
resistance and failing. I find that the transmitter works first thing and,
after everything is up and running, it stops modulating.

I'm going to try connecting the radio directly to the battery bus, via fuse,
upstream of the master switch and see if that takes care of the problem.

I've been wanting to replace the single DPDT switch with two SPST switches.
Then I can switch batteries without interrupting power.


"Andy" wrote in message
...
No luck with the new wiring. And no
luck finding the service bulletin.

Microair removed all the SBs from public access. I think that
happened when ownership changed but not sure of that.

I have several of the SB, including this one, on file and can send you
if you pm me.

Andy

Does anyone know the negative effects of connecting the mic ground to power ground instead of pin 2 on this radio? Previous owner wired my glider like that...

Does anyone know the negative effects of connecting the mic ground to power ground instead of pin 2 on this radio?

None: According to the M760 manual Rev-P that is how it's supposed to be done. I recall hearing from the repair shop that either is okay and to use what's easiest for your installation.

Interesting.

The manual for my radio calls for pin 2 to be used for the mic ground. A
friend at the airport has a later version and his has pin 2 open. I may ask
him to loan me his radio (since it's not installed in his project yet) for
troubleshooting and I've asked Graham at Microair in Australia for guidance
on wiring.


wrote in message
...
Does anyone know the negative effects of connecting the mic ground to
power ground instead of pin 2 on this radio?

None: According to the M760 manual Rev-P that is how it's supposed to be
done. I recall hearing from the repair shop that either is okay and to use
what's easiest for your installation.

I switched the dc input to the radio to the hot side of the switch (on a
terminal strip) and it seems to be working. I'll need a few successful
flights before I call it good. If it fails to modulate again, I'll ship it
to microairusa for repair.


"Dan Marotta" wrote in message
...
Thanks, Andy, but I'm not sure that will be necessary.

Microair sent me the applicable SB *and* put me in contact with the Rick
at Microairusa.com.

When I bought my glider it had a rather delicate master switch and, since
then, I've added a transponder. I'm wondering if the switch can not
handle the extra current of the transponder and/or is slowly increasing in
resistance and failing. I find that the transmitter works first thing
and, after everything is up and running, it stops modulating.

I'm going to try connecting the radio directly to the battery bus, via
fuse, upstream of the master switch and see if that takes care of the
problem.

I've been wanting to replace the single DPDT switch with two SPST
switches. Then I can switch batteries without interrupting power.


"Andy" wrote in message
...
No luck with the new wiring. And no
luck finding the service bulletin.

Microair removed all the SBs from public access. I think that
happened when ownership changed but not sure of that.

I have several of the SB, including this one, on file and can send you
if you pm me.

Andy

On Apr 1, 6:29*pm, "Dan Marotta" wrote:
I switched the dc input to the radio to the hot side of the switch (on a
terminal strip) and it seems to be working. *I'll need a few successful
flights before I call it good. *If it fails to modulate again, I'll ship it
to microairusa for repair.


Dan - It seems hard to believe that the switch is your glider is so
"weak" that it cannot handle the amperage of your instruments. When
you say "delicate" could the switch be damaged? If it is intermittent
it could have built up some oxidation or carbon which is acting like a
resistor limiting the voltage to your devices. I've never seen this
myself but it is possible. Of course replacing the switch with
something NOT from Radio Shack is the next approach. Look for name
brands like Switchcraft, Alco or C&K. Maybe I am stating the obvious.

- John

Thanks, John.

The switch was already installed in my glider when I bought it and I've
upped the current demand with the installation of the transponder.

It's my intent (someday) to replace the DPDT with a couple of SPST switches
(one for each battery) and I'll buy them at the local electronics supply
store, not Radioshack (and they'll be beefy, literally and figuratively, and
designed for dc).

In the mean time, I find a 1.1v drop when all equipment is turned on and I
key the mic (down to about 13.9v), but that shouldn't prevent modulation.
My 14v battery is about 2 years old and is maintained on a smart charger.


"JohnDeRosa" wrote in message
...
On Apr 1, 6:29 pm, "Dan Marotta" wrote:
I switched the dc input to the radio to the hot side of the switch (on a
terminal strip) and it seems to be working. I'll need a few successful
flights before I call it good. If it fails to modulate again, I'll ship it
to microairusa for repair.


Dan - It seems hard to believe that the switch is your glider is so
"weak" that it cannot handle the amperage of your instruments. When
you say "delicate" could the switch be damaged? If it is intermittent
it could have built up some oxidation or carbon which is acting like a
resistor limiting the voltage to your devices. I've never seen this
myself but it is possible. Of course replacing the switch with
something NOT from Radio Shack is the next approach. Look for name
brands like Switchcraft, Alco or C&K. Maybe I am stating the obvious.

- John

On Tuesday, April 2, 2013 at 9:38:04 AM UTC-7, Dan Marotta wrote:
Thanks, John.

The switch was already installed in my glider when I bought it and I've
upped the current demand with the installation of the transponder.

It's my intent (someday) to replace the DPDT with a couple of SPST switches
(one for each battery) and I'll buy them at the local electronics supply
store, not Radioshack (and they'll be beefy, literally and figuratively, and
designed for dc).

In the mean time, I find a 1.1v drop when all equipment is turned on and I
key the mic (down to about 13.9v), but that shouldn't prevent modulation.
My 14v battery is about 2 years old and is maintained on a smart charger.


"JohnDeRosa" wrote in message
...
On Apr 1, 6:29 pm, "Dan Marotta" wrote:
I switched the dc input to the radio to the hot side of the switch (on a
terminal strip) and it seems to be working. I'll need a few successful
flights before I call it good. If it fails to modulate again, I'll ship it
to microairusa for repair.


Dan - It seems hard to believe that the switch is your glider is so
"weak" that it cannot handle the amperage of your instruments. When
you say "delicate" could the switch be damaged? If it is intermittent
it could have built up some oxidation or carbon which is acting like a
resistor limiting the voltage to your devices. I've never seen this
myself but it is possible. Of course replacing the switch with
something NOT from Radio Shack is the next approach. Look for name
brands like Switchcraft, Alco or C&K. Maybe I am stating the obvious.

- John

1.1 V is a very large voltage drop. I would find where in the power distribution the largest portion of this drop is occurring and fix it. You are probable drawing 1 A in transmit, so 1.1 V equates to 1.1 ohm, a huge number for any power distribution component. If you have a good DVM you could just measure the resistance of the wiring. If not, just measure the voltage drop of each part of the wiring.

Tom