Comm radio Tx problem

[Piper J3]

I have a SL40 in my RV-12 per stock installation. The radio had a problem about twenty hours ago and then it went away and now its back again.

The radio has static and the Tx light flickers in rhythm with the static. It also seems to be in rhythm with engine speed. Faster engine ? faster flicker / static. No static and excellent radio operation with engine off. What could be making the Tx flicker on/off other than the PTT switch? I?m at a real lost here. Is there any radio adjustments that would effect this? Tomorrow I intend to remove engine cowl and look for loose plug wire. Would a high voltage ignition spark or bad sparkplug cause this? Problem is happening 90% of the time but about 10% of time radio works well even with engine running.

Any help appreciated?

 

[Piper J3]

I sent synopsis of problem to Garmin and got this reply....

I believe the SL40 squelch is opening due to noise in the aircraft electrical system. There is a procedure in the attached SL40 installation manual for adjusting the level at which the SL40 squelch opens. You should also verify all shield wires are properly terminate. If adjusting squelch and verifying no installation issues you?ll need to isolate which aircraft electrical system is inducing noise into the audio system causing the squelch to open.

 

[Mich48041]

Squelch is related to receiving. I do not know why the squelch setting would make the TX light flicker.
Pull the radio out of its tray and then slide it back in and make sure that it is fully seated. Others have had problems with the radio not fully inserted into the tray. It might look OK but could go back in further. The locking latch, that requires a hex wrench, is tricky to get seated correctly.
The majority of electrical problems are due to bad connections.

 

[Flying again!]

Fixed Problems with my SL40

I had problems with my SL30 and SL40 including intermittent reception, noise, no side tone. They were checked at the radio shop and were ok. I bought some DeOxit D5 and sprayed it on the contacts on the radio and tray side. I removed and replaced the radios a couple of times to make sure the D5 had a chance to clean any corrosions on the contacts. When powered up they worked like a champ with no further problems since then (over 2 years ago).

Here is a link to the DeOxit:

http://www.amazon.com/CAIG-DeOxit-C...ie=UTF8&qid=1461176772&sr=8-4&keywords=deoxit

I have used this to fix light bulb failure warinings on a 1995 BMW, my 20 year old washing machine lid contact, an old home radio etc. It is great stuff for cleaning corrosion from contacts and protecting them from further corrosion.

Cheap fix - Try it

TJ

 

[Piper J3]

Thanks guys. I also questioned Garmin's response. Perhaps they did not fully read my description or my wording was poor.

Anyway, I may be on to something... Yesterday I fiddled with the wiring bundle that comes up from the center tunnel and protrudes into the bottom of the radio bay. I can aggravate the problem, and better yet, make it go away just by moving some wires. So I think I either have an intermittent short to ground on the PTT (chafe or pinch) or bad connection up to the radio tray. Rain for the next four days so I?ll pull things apart and trace the problem to its source.

Thanks for ?listening?

 

[jdeas]

Tx trigger on the mic sleeve

Check your wiring to the mic sleeve as it is the trigger for the TX. I had a SL30 do almost the identical thing. It turned out to be a ground problem due to my paranoid grounding scheme..

Test by using a jumper to tie the mic sleeve to GND and see if the TX goes away.

 

[Piper J3]

Update... I fixed my comm radio Tx problem. See FlightCom 403 thread below where I found loose nut rattling around inside the FlightCom 403 intercom. Today I replaced the intercom with a used unit purchased on eBay and now my comm radio works great. Very solid Tx/Rx.