Garmin 225 Comm intermittent TRX failure

[ESW]

I have a 5 yo garmin225 comm. I am struggling with intermittent transmit failure for past several months. We've replaced PTT and cannot find anything obviously wrong with exterior wiring. The unit will test fine on ground with engine running, but fails early in flight. (This then requires aborting the mission, calling for light signals for return etc so not good!)There is no audio panel and the install just uses the internal intercom so it's quite a simple setup. The plane has an alternator and all lighting, strobe etc is modern lighting, new battery, so I beleive the issue is either in the radio or rack connections. Any suggestions on way to isolate this problem and resolve would be appreciated. ESW , Ifly out of LHD

 

[AvNavCom]

This then requires aborting the mission, calling for light signals for return etc so not good!

My first thought is that you should invest in a handheld radio so light signals are unnecessary. Great back-up in normal times, and essential if you're troubleshooting airborne radio problems, I'd say.

I'll leave the troubleshooting advice to the board A&Ps.

 

[Bell206]

I am struggling with intermittent transmit failure for past several months

So up to that point no other issues? Was there any work performed on aircraft just prior to that point?

The unit will test fine on ground with engine running, but fails early in flight.

By intermittant, you mean it always works on the ground via both PTT switches, but always fails just after airborne?

good!)There is no audio panel and the install just uses the internal intercom so it's quite a simple setup.

Does the intercom system still work when airborne?

 

[ESW]

1. There is no external intercom. The 2 place intercom is internal to the radio. And it is functional when TX function is failed.
2. I've had various failures before and after takeoff. I've had to abort about 6 missions.
3. There is a pattern tho of successful radio checks followed by a subsequent transmit failure, either before takeoff (i.e. after taxi and runup) or sometime subsequent while flying. Occasionally the TX function has returned during flight.
4. Receive always works.
5. When radio is working it works well, good reception and range etc.
6. I have a handheld radio

 

[ESW]

Reply continued:
7. I had some panel work some months prior not directly involving the radio. There was a time lag tho before these problems started showing up.

 

[MooneyDriver78]

I had a similar problem, turned out to be a bad circuit breaker.
It passed continuity test but when transmitting, the extra current draw the radio required it wouldn’t allow the current to pass.

 

[AvNavCom]

When you hit the PTT during transmit failure, does the "TX" symbol light up on the radio? That may help discriminate between a pre-device issue and an internal/post-device issue. Receive always works, which suggests antenna continuity.

Regarding my handheld radio comment, perhaps I misunderstood about the light signals, which suggested to me an inability to communicate via radio.

 

[ESW]

Thanks avnavcom
The TX does Not light up if tx has failed. So perhaps we are looking at internal to the radio,

 

[Bell206]

I had some panel work some months prior not directly involving the radio. There was a time lag tho before these problems started showing up.

In my experience, anytime there's work done behind the panel regardless the reason, its a good place to start looking. Given your description it could be as simple as a loose connection or similar issue. Perhaps start by removing the radio from the rack and check all the connections for cleanliness and obvious damage, both on the radio and in the rack. Then check the coax to the antenna. Once you're satisfied the radio is good and firmly secured in the rack and the coax is serviceable from the radio to the antenna, take it for a spin and see if there is any difference or if it stays the same.

 

[ESW]

Thank you bell206. We have been re racking cleaning contacts examining connections several times over the course of these failures and result is that we can pass a ground radio check afterwards both with engine off and while running, but then have a subsequent failure..

 

[wilkersk]

When you hit the PTT during transmit failure, does the "TX" symbol light up on the radio?

^^^This is the first thing to check. When the gripe is happening, look for the TX icon on the display. If it is illuminating consistently, your problem is not in the PTT circuit. If it is not illuminating then dollars to donuts it is the PTT circuit. But there's more to it than just the PTT button on the yoke. Gotta know how its physically wired to start with if that's the case.

 

[AvNavCom]

Thanks avnavcom
The TX does Not light up if tx has failed. So perhaps we are looking at internal to the radio,

That's actually very helpful. If you're seeing TX light up during normal function, but not during your transmission failures, that finding shows that the radio is not trying to transmit (hence the lack of a notification) vice trying to transmit (TX lights up) but the signal is not going out (which would suggest an antenna issue). That significantly reduces the probability space of where the fault is. As the esteemed @Bell206 suggests given the provided history, I agree with @wilkersk that my money would be on a loose connection somewhere in the PTT circuit. Logic dictates that something is intermittently failing between your digit on the PTT and whatever bit is getting flipped inside the radio to put it into a transmit state. Good luck!

 

[wilkersk]

The standard way of wiring the PTT ground is through the mic audio low circuit on the mic jack which allows you to plug in an external PTT, like the ones we used to use when most aircraft still had hand-held mics. This wiring is often a source of intermittent problems with PTT because of poor soldering.

 

[Bell206]

We have been re racking cleaning contacts examining connections several times over the course of these failures and result is that we can pass a ground radio check

Did you check the coax connection at the antenna? Is your COMM antenna on the belly? Sometimes when the transmit system works on the ground but not in the air is can be a grounding issue at the antenna. Unfortunately, without a RF watt meter to see what power the radio is actually putting out tough to move forward. One option, is to see if you can borrow a similar antenna and see if that makes a difference.

 

[AvNavCom]

Did you check the coax connection at the antenna? Is your COMM antenna on the belly? Sometimes when the transmit system works on the ground but not in the air is can be a grounding issue at the antenna. Unfortunately, without a RF watt meter to see what power the radio is actually putting out tough to move forward. One option, is to see if you can borrow a similar antenna and see if that makes a difference.

If it was an issue with the coax connection to the antenna, would you still expect that to affect the TX notification on the radio when he hits the PTT switch? Genuine request for information, as I'm not sure if the transmit notification on the radio reflects just PTT input ("I acknowledge that you're trying to transmit") or whether it acknowledges that the output is functioning properly.

 

[Bell206]

would you still expect that to affect the TX notification on the radio when he hits the PTT switch?

Yes and no. If the radio transmit power is not fully "expelled" from the antenna, it can cause some interesting things internally. And considering the majority of transmit problems are antenna/coax/connection/corrosion related, checking these items can be done without any special equipment. And since the radio does transmit on the ground which can be a sign of low output power, the antenna coax, antenna, and antenna mount area are usually my first place to check after an initial review of the system.

 

[AvNavCom]

Yes and no. If the radio transmit power is not fully "expelled" from the antenna, it can cause some interesting things internally. And considering the majority of transmit problems are antenna/coax/connection/corrosion related, checking these items can be done without any special equipment. And since the radio does transmit on the ground which can be a sign of low output power, the antenna coax, antenna, and antenna mount area are usually my first place to check after an initial review of the system.

Thanks for the informative reply! I like to learn what I can from A&Ps when the opportunity presents itself!

 

[Clip4]

Who installed this radio?

 

[ESW]

Hi thanks for all the suggestions and trouble shooting. Especially information on grounding of PTT circuits. I have had the pilot PTT totally retired back to the tray and new PTT switch. Without materially affecting the outcome. Additionally I have a plug in PTT on the right side. They both are equally affected. That is when I cannot transmit both PTT are affected. And when I can both work. Also when working I have good reception and coverage. No flickering fading or loss of reception.The radio was installed by AP/IA and a radio tech. Not garmin dealer.

So as of today a garmin dealer is going thru the wiring of the radio tray wire by wire, and he shipped the radio to his home shop to run a bench test on the radio.

To me this seems almost like a temperature issue, i.e. when the radio warms up TX fails. however the radio is kind of by itself not in a stack, and it worked fine for approximately 5 years. Also ambient temperatures are low here in Alaska. Not like the windscreen is trapping a bunch of rays. So it's puzzling to say the least.

I'll keep the group posted on what I find out and thanks again for the suggestions.

 

[ESW]

Hi interim progess post:
1. Radio itself successfully bench tested at garmin dealer. Garmin dealer inspect wiring and all apparently ok and properly configured including PPT and earphone jacks.
2. Reinstall and use alternate antenna. (I have 2 antennas)
3. Same result.
4. Garmin dealer now believes that this must be a pin connector problem, and will inspect/troubleshoot again this week.
5. One more aborted mission and NORDO RTB. The tower has been v. good to work with, but I don't want to continue causing problems with them. So hopefully we'll make some substantial progress this week.
Cheers, Scott.

 

[WDD]

I had a somewhat similar issue with my COM 2; an intermittent failure when transmitting. Turned out it was an old / bad connector plug for the antenna wire to the radio. Worked fine on the ground, but in the air with the vibrations and what not it would cut out. Have you replaced that / wired a new one in by any chance?

Did you check the coax connection at the antenna? Is your COMM antenna on the belly? Sometimes when the transmit system works on the ground but not in the air is can be a grounding issue at the antenna. Unfortunately, without a RF watt meter to see what power the radio is actually putting out tough to move forward. One option, is to see if you can borrow a similar antenna and see if that makes a difference.

 

[AvNavCom]

5. One more aborted mission and NORDO RTB. The tower has been v. good to work with, but I don't want to continue causing problems with them.

How are you NORDO if you're carrying a hand-held radio?

 

[MackMooney]

hmm, may be a dumb question, but have you checked the ptt buttons? could one or both be faulty

 

[ESW]

Avnavcom, I do have a hand held. But I spose I lack confidence in it. It doesn't transmit very well and others have a hard time hearing me. In this instance I felt it was better to land at a nearby uncontrolled field, call the tower and proceed inbound relying on receiving their calls and using transponder ident to reply. Which the tower suggested. I do now have a remote antenna connection for handheld and finally got the earphone jack adapter. I checked it from the airport and it does work. So if this occurs again I'll use it. Thanks.

 

[AvNavCom]

Avnavcom, I do have a hand held. But I spose I lack confidence in it. It doesn't transmit very well and others have a hard time hearing me. In this instance I felt it was better to land at a nearby uncontrolled field, call the tower and proceed inbound relying on receiving their calls and using transponder ident to reply. Which the tower suggested. I do now have a remote antenna connection for handheld and finally got the earphone jack adapter. I checked it from the airport and it does work. So if this occurs again I'll use it. Thanks.

Sounds good. I was a little confused, as I know a fair number of people fly with a handheld as their primary radio in older planes with no electrical systems so the NORDO thing threw me off. The remote antenna connection is awesome. I imagine it will give you much more range. Personally, I have a PJ2+ handheld specifically so I can plug my headset directly into it if I have a comms failure. Thanks for clearing that up. Interesting scheme with the transponder ident to acknowledge tower directions. I haven't seen that before.

 

[theplanesalon]

We just removed a faulty PTT button from a customer's plane yesterday - intermittent.
One of the wires had come off on the other end - no environmental splice/solder sleeve, just a barrel crimp.
One of the Comm Radio Pins was also bent at the tray in the connector.

Things happen....

 

[ESW]

Plane salon. Thanks for this reply. I have had PTT replaced wired back to the tray by a garmin dealer. Next plan is to investigate the connector pins.

 

[dmspilot]

You haven't tried a different radio yet?

 

[ESW]

See my #20, item.1. The radio was successfully bench tested.

 

[dmspilot]

See my #20, item.1. The radio was successfully bench tested.

You also said it only fails in the air and not on the ground. So that doesn't count.

 

[ESW]

Thanks DMS,
It's a complex set of observations over 6 or 7 occurrences. My OP summarizes the issue, also see my #4, 5 and 20.
1. We have two new PTT, one completely newly wired to tray , and one a jack plug-in type.
2. The comm will at times fail on ground and at times in air after a few minutes to half hour or so.
3. The radio itself has been successfully bench tested by Garmin dealer.
4. I have a plane power alternator (6 years old) and panel voltmeter and am getting good charging and good voltage readings. Also battery is only about 8 months old as well.
5. I have attempted a sortie using a separate antenna that was already installed in the plane. With no change in result.

Could you clarify your post "bench test doesn't count in air" Im not really understanding what you're getting at there?
Thanks ESW

 

[dmspilot]

What I'm getting at is a bench test proves nothing when you have an intermittent problem. Swapping out the radio with a different one and testing it in the airplane for an appropriate amount of time is the only way to ensure the radio is not the problem.

 

[ESW]

Hi I wanted to report that I have a working radio. Thanks for timely advice thru the forum. Results were: tighten ground, tray mounting, back of tray screws, and pin connector screws and bench test radio as good. So overall a simple problem of screws working loose over 5 00 hrs.. looking back it seems I should have been able to sort this myself w/o engaging a mechanic. But when looking at the installation I kind of lost confidence I could work this out successfully myself. So live and learn I spose..thanks for the helpful advice, Scott.

 

[ESW]

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