Microair M760 Intermittentent Transmit

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

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

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.

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