Microair M760 Intermittentent Transmit

[Dan Marotta]

Reception is good and, until recently, transmission has been good, as well.
Lately, transmission has been intermittent. The radio transmits carrier,
but no modulation. I have gotten a few false starts since one time moving
the boom microphone caused it to transmit again. Thinking of frayed,
chafed, or broken wires, I dismantled the mic but found nothing wrong.
Looking further, I found numerous splices in the mic wire and I'm in process
of replacing it in its entirety.

With the mic wires cut, I measured around 9.5 Vdc between the conductor and
the shield (pins 1 and 2 of the DB15 connector.

A friend happened by and told me that he had heard that Microair radios of
my vintage had a known problem wherein there were two circuit boards mounted
at right angles to each other and, over time, vibration could cause a
connection to break. Has anyone else heard this?

Is there a Microair repair facility in the US?

Thanks,
Dan, LAK-17a, 5J

[Martin[_5_]]

I'd suspect the wiring before the radio's internals. I just repaired this very problem on my identical radio this weekend. It was one broken wire (mike audio ground) and one frayed wire (mike audio signal). Look for bad crimps or solder joints all the way to the back of the radio.

[slbair]

I've had the same problem which was caused by low voltage from the battery. Micro air is sensitive to this.

SLB

[[email protected]]

Hi Dan,
I have the same glider and radio. Nick can fix basic stuff on it, as he did for me.
Nick Popovski
Peninsula Avionics, Inc.
www.peninsulaavionics.com

On a previous glider I had the carrier wave only problem on a Becker 4201 (twice). It required a s/w reflash, twice.
~Bruce

[[email protected]]

On Tuesday, March 26, 2013 8:35:26 PM UTC-4, Dan Marotta wrote:
> Reception is good and, until recently, transmission has been good, as well. Lately, transmission has been intermittent. The radio transmits carrier, but no modulation. I have gotten a few false starts since one time moving the boom microphone caused it to transmit again. Thinking of frayed, chafed, or broken wires, I dismantled the mic but found nothing wrong. Looking further, I found numerous splices in the mic wire and I'm in process of replacing it in its entirety. With the mic wires cut, I measured around 9.5 Vdc between the conductor and the shield (pins 1 and 2 of the DB15 connector. A friend happened by and told me that he had heard that Microair radios of my vintage had a known problem wherein there were two circuit boards mounted at right angles to each other and, over time, vibration could cause a connection to break. Has anyone else heard this? Is there a Microair repair facility in the US? Thanks, Dan, LAK-17a, 5J

This is a common symptom of a problem with the socket that the main processor chip seats in. There was a tech note on how to clear this symptom by removal, cleaning of contacts, and reinstalling.
A later service bulletin defines a more permanent fix to be done by repair shops.
UH

[Dan Marotta]

Thanks.

As I said, I've found at least three (3) splices in the mic wire and, where
the mic wire connects to the Microair supplied harness behind the panel, the
connections are made with crimps. I'm in the process of replacing all of
that with new shielded mic wire.

I'm the duty tow pilot today but, since there's nothing on the schedule,
I'll be working on my glider. Maybe I'll get lucky.


"Martin" > wrote in message
...
I'd suspect the wiring before the radio's internals. I just repaired this
very problem on my identical radio this weekend. It was one broken wire
(mike audio ground) and one frayed wire (mike audio signal). Look for bad
crimps or solder joints all the way to the back of the radio.

[Dan Marotta]

Batteries freshly charged. I get strong carrier transmission but no
modulation. Of course I have no proper test equipment.


"slbair" > wrote in message
...
> I've had the same problem which was caused by low voltage from the
> battery. Micro air is sensitive to this.
>
> SLB

[Dan Marotta]

Do you have any information on the tech note? I'll be searching the web...

<snip>

This is a common symptom of a problem with the socket that the main
processor chip seats in. There was a tech note on how to clear this symptom
by removal, cleaning of contacts, and reinstalling.
A later service bulletin defines a more permanent fix to be done by repair
shops.
UH

[Dan Marotta]

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

I've brought the radio home and will be shipping it off for repair and or
updating.


"Dan Marotta" > wrote in message
...
> Do you have any information on the tech note? I'll be searching the
> web...
>
> <snip>
>
> This is a common symptom of a problem with the socket that the main
> processor chip seats in. There was a tech note on how to clear this
> symptom by removal, cleaning of contacts, and reinstalling.
> A later service bulletin defines a more permanent fix to be done by repair
> shops.
> UH

[Dan Marotta]

Update: Taking off the front panel and pressing the processor chip into its
socket seems to have solved my problem. Thankfully there's no need for
shipping.


"Dan Marotta" > wrote in message
...
> No luck with the new wiring. And no luck finding the service bulletin.
>
> I've brought the radio home and will be shipping it off for repair and or
> updating.
>
>
> "Dan Marotta" > wrote in message
> ...
>> Do you have any information on the tech note? I'll be searching the
>> web...
>>
>> <snip>
>>
>> This is a common symptom of a problem with the socket that the main
>> processor chip seats in. There was a tech note on how to clear this
>> symptom by removal, cleaning of contacts, and reinstalling.
>> A later service bulletin defines a more permanent fix to be done by
>> repair shops.
>> UH
>

[[email protected]]

On Friday, March 29, 2013 11:30:30 AM UTC-4, Dan Marotta wrote:
> Update: Taking off the front panel and pressing the processor chip into its socket seems to have solved my problem. Thankfully there's no need for shipping. "Dan Marotta" > wrote in message ... > No luck with the new wiring. And no luck finding the service bulletin. > > I've brought the radio home and will be shipping it off for repair and or > updating. > > > "Dan Marotta" > wrote in message > ... >> Do you have any information on the tech note? I'll be searching the >> web... >> >> <snip> >> >> This is a common symptom of a problem with the socket that the main >> processor chip seats in. There was a tech note on how to clear this >> symptom by removal, cleaning of contacts, and reinstalling. >> A later service bulletin defines a more permanent fix to be done by >> repair shops. >> UH >

That is what the service bulletin described.
Problem will eventually return, but this works until you get permannt mod.
UH

[Dan Marotta]

I spoke with the man at Microairusa.com and he told me that the problem was
with radios manufactured with the older black socket and not the newer brown
socket. Mine has a brown socket.

It's a much smaller price to remove a couple of screws and push than to pack
and ship the unit (which I will do if the "push" doesn't restore it to life
should the problem resurface).

> wrote in message
...
On Friday, March 29, 2013 11:30:30 AM UTC-4, Dan Marotta wrote:
> Update: Taking off the front panel and pressing the processor chip into
> its socket seems to have solved my problem. Thankfully there's no need for
> shipping. "Dan Marotta" > wrote in message
> ... > No luck with the new wiring. And no
> luck finding the service bulletin. > > I've brought the radio home and
> will be shipping it off for repair and or > updating. > > > "Dan Marotta"
> > wrote in message >
> ... >> Do you have any information on the
> tech note? I'll be searching the >> web... >> >> <snip> >> >> This is a
> common symptom of a problem with the socket that the main >> processor
> chip seats in. There was a tech note on how to clear this >> symptom by
> removal, cleaning of contacts, and reinstalling. >> A later service
> bulletin defines a more permanent fix to be done by >> repair shops. >> UH
> >

That is what the service bulletin described.
Problem will eventually return, but this works until you get permannt mod.
UH

[Andy[_1_]]

> 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

[Dan Marotta]

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

[Dan Marotta]

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
>

[dbrunone]

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...

[[email protected]]

> 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.

[JohnDeRosa]

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

[Dan Marotta]

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.

[Dan Marotta]

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

[[email protected]]

Hi Dan, I also found interesting/scary the differences in the radio and manual revisions. To end my worries of the unknown radio version (last owner had it updated at Microair) I pinned it out with a meter and finally used pin-2. This helped me terminate the shield easier.
Regarding your power switch, replace it with new ones from Craggy , A-C Spruce, etc. The one on my 24 literally sprang open at the back; Yikes!
If you have any generic I/P wiring questions Richard at Craggy is very nice and knowledgable, so is Rick at Erie aviation. I hope your recent fix works full time, I'm still struggling with the crappy antenna installation, sigh.......
~Bruce
Lak17AT

[[email protected]]

On Tuesday, April 2, 2013 at 4:46:45 PM UTC-7, wrote:
> Hi Dan, I also found interesting/scary the differences in the radio and manual revisions. To end my worries of the unknown radio version (last owner had it updated at Microair) I pinned it out with a meter and finally used pin-2. This helped me terminate the shield easier.
> Regarding your power switch, replace it with new ones from Craggy , A-C Spruce, etc. The one on my 24 literally sprang open at the back; Yikes!
> If you have any generic I/P wiring questions Richard at Craggy is very nice and knowledgable, so is Rick at Erie aviation. I hope your recent fix works full time, I'm still struggling with the crappy antenna installation, sigh.......
> ~Bruce
> Lak17AT

I Trailered my Safari Helicopter over 150,000 miles in support of the Experimental Helo Magazine that I produced. The only "trailer induced" failure I ever had was the MicroAire Radio. I got to the point that I would carry a spare in a foam filled box and just change them out at the airshow. I'm sure that my MicroAire qualified for "Frequent Flyer" miles from its trips to AU. I'm again looking at them because some of their features are quite nice for HOTAS helicopter operation. Looking for more recent experiences with the MicroAire (Q)
stu fields

[Charlie M. (UH & 002 owner/pilot)]

On Wednesday, March 27, 2013 at 8:40:46 AM UTC-4, wrote:
> On Tuesday, March 26, 2013 8:35:26 PM UTC-4, Dan Marotta wrote:
> > Reception is good and, until recently, transmission has been good, as well. Lately, transmission has been intermittent. The radio transmits carrier, but no modulation. I have gotten a few false starts since one time moving the boom microphone caused it to transmit again. Thinking of frayed, chafed, or broken wires, I dismantled the mic but found nothing wrong. Looking further, I found numerous splices in the mic wire and I'm in process of replacing it in its entirety. With the mic wires cut, I measured around 9.5 Vdc between the conductor and the shield (pins 1 and 2 of the DB15 connector. A friend happened by and told me that he had heard that Microair radios of my vintage had a known problem wherein there were two circuit boards mounted at right angles to each other and, over time, vibration could cause a connection to break. Has anyone else heard this? Is there a Microair repair facility in the US? Thanks, Dan, LAK-17a, 5J
>
> This is a common symptom of a problem with the socket that the main processor chip seats in. There was a tech note on how to clear this symptom by removal, cleaning of contacts, and reinstalling.
> A later service bulletin defines a more permanent fix to be done by repair shops.
> UH

You can follow-up with UncleHank, but I did a "fix" on his MicroAir (2 years ago?) to resolve this issue. Basically a through cleaning and used a "stereo enhancement fluid" for the chip pins.
He can let you know if it's still fixed.

[2G]

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