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Comm won't transmit

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mbrenner(at)htc.net
Guest

Posted: Wed Aug 01, 2007 10:06 am Post subject: Comm won't transmit

I just started flying off the test hours on my  Zodiac 601 HDS.  Everything seemed to be operating normally

  until I realized today that I'm getting a  very weak transmission on my ICOM A200 Comm.  The reception is  fine

 but today when I was trying to communicate with  another aircradft at my non-towered field it became obvious that

 the other pilot couldn't hear me.  When I got  back on the ground I asked another pilot to see if I was  transmittting.

 He said the signal was very weak on the first  transmission and then non-existent on subsequent transmissions.   The

 radio is wired through a Flightcom intercom.   I have the transmission problem regardless of whether I have the intercom  

 switched to "All" or "Iso".  Reception is fine  either way.

  

 I did notice that when I push the PTT button, the  LED on my Ray Allan trim indicator goes out, which seems rather odd  

 but may be a clue as to what is going on .  When I release the PTT button the LED comes back  on.  I'm guessing I have 

 a short in the PTT circuit but before I start  ripping things apart I'd like some opinions on  what to check first.  Thanks.

  

 Mike Brenner

 Zodiac 601 HDS

    [quote][b]

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larry(at)macsmachine.com
Guest

Posted: Wed Aug 01, 2007 11:07 am Post subject: Comm won't transmit

Mike,

Though you didn't say the trim and com buttons are in near proximity on 

the stick, I'd check that proximity and work toward isolating the com

from any wires or common connections.  It could be a wire crossing 

another, but the most logical is a connection near the switches.

Look carefully at your comm wires first working back thru to the radio 

if it's involved and fuses.  I'm using a A200 with a Sigtronics intercom 

that

had problems with the main Molex plugs and Molex Connector in the back 

of the radio.  Making good connections back there is crucial.  None of

the Molex plugs and wires in the rear of the A200 should be loose or 

wobbly.  My reception and transmit were soft until that Molex Connector and

the Molex plugs (purchased from Mouser components ) was replaced by a 

professional.



Larry McFarland 601HDS at www.macsmachine.com

Mike Brenner wrote:

 	  Quote: 	
		   I just started flying off the test hours on my Zodiac 601 HDS.  

 Everything seemed to be operating normally

  until I realized today that I'm getting a very weak transmission on 

 my ICOM A200 Comm.  The reception is fine

 but today when I was trying to communicate with another aircradft at 

 my non-towered field it became obvious that

 the other pilot couldn't hear me.  When I got back on the ground I 

 asked another pilot to see if I was transmittting.

 He said the signal was very weak on the first transmission and then 

 non-existent on subsequent transmissions.  The

 radio is wired through a Flightcom intercom.  I have the transmission 

 problem regardless of whether I have the intercom

 switched to "All" or "Iso".  Reception is fine either way.

  

 I did notice that when I push the PTT button, the LED on my Ray Allan 

 trim indicator goes out, which seems rather odd

 but may be a clue as to what is going on . When I release the PTT 

 button the LED comes back on.  I'm guessing I have

 a short in the PTT circuit but before I start ripping things apart I'd 

 like some opinions on what to check first.  Thanks.

  

 Mike Brenner

 Zodiac 601 HDS

 *



 *

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frank.hinde(at)hp.com
Guest

Posted: Wed Aug 01, 2007 11:17 am Post subject: Comm won't transmit

My first guess is you have a bad ground. The ICOM will  consume the most power when it is transmitting. The fact that it does something  weired with a totally unrelated piece of equipment  when demanding a lot of  current normally always means bad grounding.

  

 Frank Rv7a...Ex Zenair Zodiac  601HDS.



   From:  owner-aeroelectric-list-server(at)matronics.com  [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Mike  Brenner

Sent: Wednesday, August 01, 2007 10:58 AM

To:  aeroelectric-list(at)matronics.com

Subject: Comm won't  transmit

 

 I just started flying off the test hours on my  Zodiac 601 HDS.  Everything seemed to be operating normally

  until I realized today that I'm getting a  very weak transmission on my ICOM A200 Comm.  The reception is  fine

 but today when I was trying to communicate with  another aircradft at my non-towered field it became obvious that

 the other pilot couldn't hear me.  When I got  back on the ground I asked another pilot to see if I was  transmittting.

 He said the signal was very weak on the first  transmission and then non-existent on subsequent transmissions.   The

 radio is wired through a Flightcom intercom.   I have the transmission problem regardless of whether I have the intercom  

 switched to "All" or "Iso".  Reception is fine  either way.

  

 I did notice that when I push the PTT button, the  LED on my Ray Allan trim indicator goes out, which seems rather odd  

 but may be a clue as to what is going on .  When I release the PTT button the LED comes back  on.  I'm guessing I have 

 a short in the PTT circuit but before I start  ripping things apart I'd like some opinions on  what to check first.  Thanks.

  

 Mike Brenner

 Zodiac 601 HDS

[quote]



href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matronics.com/Navigator?AeroElectric-List

href="http://forums.matronics.com">http://forums.matronics.com



[b]

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aadamson(at)highrf.com
Guest

Posted: Wed Aug 01, 2007 12:07 pm Post subject: Comm won't transmit

Mike, it sounds like you are getting RFI into other things when

transmitting... I'd suspect the antenna connector(ions).  While it might RX

just fine, a bad connection will make TX flaky and will spew RFI around that

will make trim indicators do odd things and other things work funky too.

Check the Sheild on the connector and also the center pin and remember, just

because it shows good at DC, doesn't mean it works at RF.



Alan 



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mbrenner(at)htc.net
Guest

Posted: Wed Aug 01, 2007 1:51 pm Post subject: Comm won't transmit

Larry,

  

 The trim switch and LED are both on the panel and  PTT is on the stick so I'm pretty sure it isn't a switch crossover  problem.  I will check the ground and the connector tomorrow.  I also  have a headset with a PTT button on one of the ear muffs.  I've never used  it before but I'll try transmitting with that and see what happens.

  

 Mike Brenner

    [quote][b]

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mprather(at)spro.net
Guest

Posted: Wed Aug 01, 2007 3:12 pm Post subject: Comm won't transmit

Hello Mike,



I sort of doubt that the problem is actually with the PTT button.. 

Looking at the manual for the radio:



http://www.icomamerica.com/downloads/manuals/avionics/ic-a200.pdf



I notice that the display has a "TX" indicator which should be visible

whenever the transmit circuit is being selected by the PTT button.  I'd

guess that a problem with the PTT would cause the "TX" indicator to

flicker, and the output to be noisy, but have normal strength..



I agree with the other posters that have suggested checking the RF side of

things.  It appears that energy broadcast from the antenna is low, and

likely is being lost within the airframe - as evidenced by other circuitry

being affected - trim circuit.



A few questions:



 - Is this overall installation typical of other 601's?

 - Is the antenna mounted to an aluminum skin?

 - What kind of antenna are you using?

 - What's the cable routing like?

 - What kind of coax and connectors are you using?

 - Do you have a copy of the Aeroelectric Connection?



Good luck..  Let us know what you find.

Thanks,



Matt-

 	  Quote: 	
		   I just started flying off the test hours on my Zodiac 601 HDS.  Everything

 seemed to be operating normally

  until I realized today that I'm getting a very weak transmission on my

 ICOM A200 Comm.  The reception is fine

 but today when I was trying to communicate with another aircradft at my

 non-towered field it became obvious that

 the other pilot couldn't hear me.  When I got back on the ground I asked

 another pilot to see if I was transmittting.

 He said the signal was very weak on the first transmission and then

 non-existent on subsequent transmissions.  The

 radio is wired through a Flightcom intercom.  I have the transmission

 problem regardless of whether I have the intercom

 switched to "All" or "Iso".  Reception is fine either way.



 I did notice that when I push the PTT button, the LED on my Ray Allan trim

 indicator goes out, which seems rather odd

 but may be a clue as to what is going on . When I release the PTT button

 the LED comes back on.  I'm guessing I have

 a short in the PTT circuit but before I start ripping things apart I'd

 like some opinions on what to check first.  Thanks.



 Mike Brenner

 Zodiac 601 HDS

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larry(at)macsmachine.com
Guest

Posted: Wed Aug 01, 2007 4:01 pm Post subject: Comm won't transmit

Mike,

The grounds on that Molex plug need to be solid and not wobbly.  Frank 

is right about the grounding. Molex contact terminals in that plug

are easy to bend and foul.  The wires should feel secure and not "loose 

in a hole".  Placing the wiring for these plugs is something I screwed up

badly. The Molex plug that is part of the A200 mounting rack is one that 

the buyer/builder gets to wire and that was the part that

gave me all the trouble. See image of Molex plug on mount rack.  I have 

a removable forward top skin, so the fix was only difficult

to get to from above between tank and radio rack.  I found the 

transmission signal would go quiet to very loud when I fingered the 

loose ground

wires coming out of this Molex plug which ultimately was replaced as 

were the contact terminals. I'd suggest you turn it on and "finger those 

wires"

coming out of the plug to see if your signal strength changes on transmit.



http://www.macsmachine.com/images/electrical/full/encoder.gif



Good luck,



Larry



Mike Brenner wrote:

 	  Quote: 	
		   Larry,

  

 The trim switch and LED are both on the panel and PTT is on the stick 

 so I'm pretty sure it isn't a switch crossover problem.  I will check 

 the ground and the connector tomorrow.  I also have a headset with a 

 PTT button on one of the ear muffs.  I've never used it before but 

 I'll try transmitting with that and see what happens.

  

 Mike Brenner

 *===============================



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