Radio not transmitting

[kgwilson]

I have a Microair M760 Revision Q radio which has been performing well since 2015. On Wednesday I landed at Casino on my way around local aerodromes doing a leaflet drop for our Wings and Wheels on 20 June & I turned on the radio after startup as normal & got a lot of noise in my ears. The green receive light was on and the noise did not stop. Squelch made no difference. I tried to transmit but the indicator light did not turn red as normal even though I heard a click when pressing the PTT. The green receive light stayed on and the noise continued through the process. I heard a couple of distant transmits and then a clear local transmit when someone joined the circuit. During the receipt of this transmission the noise went away & came back at the completion of the transmission.

 

I haven't investigated this yet but thought I'd ask if anyone else has had a similar issue.

[RFguy]

Likely :

 

The microprocessor got really confused by a spike high or spike low

or

The frequency you had dialed up had alot of interference, white noise interfering signal.

or

The your radio was overloaded by a nearby transmitter (AWIS?) that caused your radio to generate noise on your listening frequency

 

[kgwilson]

Thanks for that. Personally I think it  is likely to be something close to the first option because it doesn't matter what frequency is used the problem is the same. I've now checked the radio operation without the engine running after a day in the hangar & there is no change.  If a spike has damaged rather than confused the microprocessor what then? Microair are out of business. Is there anyone who can repair them? Maybe a replacement radio would be better than spending money on getting someone to look at & not be able to fix it.

[cscotthendry]

KGWilson:
I think your suggestion of a new radio is the go.
I had a trike with a rev Q microair radio and I'm not a fan. A really good sub that will fit in the same hole is the Trig.

[RFguy]

KG. If it is still sick (wasnt clear about whether it fixed itself when you departed casino)

 

send it down to me to look at.  PO Box 5231 Lyneham ACT2602

 

[kgwilson]

Yes it is still sick. I checked all my wiring though I didn't think that was a problem & it isn't. It is connected via a 5 amp circuit breaker but I also have an in line 2 amp fuse for it and an in line power filter between the fuse and the radio power input. I did this plus ferrite chokes at the radio and headphone jacks on installation because I was getting a bit of engine interference originally. All the comms cables are single core sheilded. I thought all this should protect it against spikes but perhaps not. I'll remove it tomorrow & set it up on the bench & go from there. 

[kgwilson]

11 hours ago, cscotthendry said:

KGWilson:
I think your suggestion of a new radio is the go.
I had a trike with a rev Q microair radio and I'm not a fan. A really good sub that will fit in the same hole is the Trig.

Yes if it is U/S the Trig is likely to be the best replacement though it does have an extra avionics tray to find a place for.

[RFguy]

yeah no worries. if you send it to me, be sure to send NO accessories. I have the jigs and connector- test harnesses made up.  very worst case it might take an hour to fix. takes longer to get screws out.

[Blueadventures]

On 06/06/2021 at 9:04 AM, RFguy said:

KG. If it is still sick (wasnt clear about whether it fixed itself when you departed casino)

 

send it down to me to look at.  PO Box 5231 Lyneham ACT2602

 

Hi RFguy my mate with a microair problem solved the issue by replacing the radio. His aircraft flew today and radio is perfect and its also a microair.  I could send the u/s one down if you interested in looking at it.  It has a service certificate by microair but never worked from the first flight a year ago.  The radio had been serviced a few years back. Regards Mike

[RFguy]

yeah send it down.
there is really only one part in there that is unobtanium. - the power amplifier module. 
I think Microair has the only stocks. So far I have not seen any dead ones.

when they come back here, i usually install a spike protection diode in them.
 

[RFguy]

posted for other's benefit :

This model radio wont transmit when the receiver is active or in fault.... 
 

had a good look at it with a microscope, wiggled pins around to see any dry joints. nothing, unplugged replugged a few critical relevent plugs. 

But I DID find a few balls of solder rolling around internally !

maybe a bumpy trip down here will do the trick...

 

I put in the spike clipper diode. They have a spot for an internal fuse but it appears to have been replaced in this model with a wire link resistor ! 😞 so I would suggest it is externally fused. with some blade fuse .  2 Amps no more.. 

 

Ya know this is a very new model, a RevQ, I have never seen one. they've cleaned up a few things quite well, and replaced the unobtainium power amplifier with something modern. pretty robust actually.

 

they still  have an obession with hot glue ....... 

[RFguy]

the only thing I really dont like is that it will not transmit when the squelch is open....(signal or noise present) 

 

that's a dumb idea. How are you supposed to get your mayday call out with some interference from a USB charger, or a stuck TX 10 km away ?

 

cant  (easily) change it, the behaviour is in the program in the microprocessor. would need to modify the squelch circuit such that, at fully CW, the squelch is still closed, (which is isnt even on super strong signal) , so not much can be done, there .

Edited June 24, 2021 by RFguy