Intermittent 'TX' problem.

Discussion in 'Electrical & Instrumentation' started by richdolby, Jan 28, 2018.

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  1. Jan 28, 2018 #1

    richdolby

    richdolby

    richdolby

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    Hi, I had a new Trig radio fitted recently. The engineer who fitted it reported that initially he had a problem with an intermittent unprompted TX with the radio. He said that he'd fixed it, but couldn't identify exactly what the problem was.

    I flew the aircraft a couple of times & then the problem resurfaced. I took a look at the install and wasn't entirely happy with it. I have now made a complete new loom (see photo) and the problem is still there.

    When first switched on the radio seems fine, and responds to either P1 or P2 PTT correctly. Then after a minute or two these ghost unprompted 'TX' surface, and get steadily worse until the TX is almost continuous. The only other possibility is the P2 PTT switch that was added at the same time as the new Trig. I checked the switch with a circuit tester and it seems fine.

    So, what could be the cause??

    View attachment IMG_5955.jpg
     
    Last edited: Feb 4, 2018
  2. Jan 28, 2018 #2

    marquartflyer

    marquartflyer

    marquartflyer

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    Can issue be duplicated on a bench setup?
     
  3. Jan 28, 2018 #3

    PittsDriver68

    PittsDriver68

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    Since the problem has occurred with two wiring harnesses, the next step is to send the radio back to the manufacturer for warranty service. Intermittent switch failure is unlikely. Sounds like when a connection in the radio warms up it malfunctions.

    A competent radio technician should be able to take one of the harnesses and see this occur on the bench. But a new unit should have a warranty and messing around with it locally just lengthens the time to repair.

    Best of luck,

    Wes
     
    richdolby likes this.
  4. Jan 28, 2018 #4

    richdolby

    richdolby

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    Wes,

    Your right - the next step is to return the unit to the manufacturer, as it's still under warranty.

    I will certainly post the outcome of this one, as I know how how these intermittent faults can be a right P.I.T.A.

    Cheers,


    Rich D.
     
  5. Jan 28, 2018 #5

    IanJ

    IanJ

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    Realized I just wrote out basically everything Wes just said, so instead: me too! I second getting it in to the manufacturer for some warranty love. :D
     
  6. Jan 29, 2018 #6

    cgzro

    cgzro

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    Peter Ashwood-Smith P

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    Only thing I could add is to check if your headset has a PTT button on it. Some have a secondary ptt .. oh and of course check the wiring at the mic jack end as shorting two of those pins is what triggers TX.
     
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  7. Feb 4, 2018 #7

    richdolby

    richdolby

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    Solved!!

    On the P2 mic jack-plug the insulation on the two electrical terminals was just touching. When the radio was switched on a short-circuit slowly developed (maybe moisture in the insulation used) causing the ghost 'TX' issue.

    Also, one of the washers that insulates the jack-plugs from the panel was missing, which may or may not have contributed to the issue.

    The radio that was in the aircraft previously was a Bendix-King. The engineer that fitted the Trig radio seems to have adopted the existing wiring loom to suit the new radio. When I made the new loom I followed the Trig Installation Manual circuit diagram.
     
    Last edited: Feb 4, 2018
  8. Feb 4, 2018 #8

    Guido Lepore

    Guido Lepore

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    Well done Peter. Mine are all converted to single helicopter jacks, seem to have less problems. Dual jacks are from the days you can't remember, of speakers and hand mikes. Trig is a pretty good unit.
     
  9. Feb 4, 2018 #9

    cgzro

    cgzro

    cgzro

    Peter Ashwood-Smith P

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    Whenever you have radio problems its always good to start cheap with some fine sandpaper to both the plug male and also the female terminals. Ive seen people waste big bucks hunting these things.

    Does not hurt to put several layers of heat shrink at those terminals also and to solder rather than just crimp. They wont break if they are well supported and stray strands wont cause strange problems.
     
    Last edited: Feb 4, 2018

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