Microair M760 Intermittentent Transmit

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

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.

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

SLB

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

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

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.

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

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

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

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