SL30 "COM FAILURE"

[Jim_R]

Unfortunately, while my plane was down for an engine overhaul, some rodents got inside it and did some damage. We repaired everything we could find, but knew that some checkouts would have to wait until after the engine was reinstalled and go fly.

On my first post-overhaul flight, my COM2 SL30 appeared to behave as normal (display looked normal, was able to change modes/freqs, etc.), but I soon realized it was not transmitting or receiving. Unfortunately, I did not notice if the TX indication lit up when PTT was pressed.

On my second post-overhaul flight, I confirmed the same (bad) SL30 behavior at the beginning of the flight. (Again, I did not notice if the TX indication lit up.) At some point several minutes into the flight, I noticed that the SL30 display was now showing COM FAILURE. This message did not appear at all during the first flight, nor was it there at the start of the second flight.

Since the message first appeared, the SL30 consistently shows COM FAILURE shortly after powerup.

I have not called Garmin, but they announced mid-last year that they would stop performing SL30 repairs by the end of 2025, so that ship has probably sailed. However, it seems more likely that there's a wiring issue external to the radio caused by the rodents.

My local avionics shop has a 4-month backlog of work. In the meantime, I'm trying to think of simple things I / my A&P could try to look at. Beyond re-racking and tracing antenna connectivity, I'm not sure what else we might be able to reasonably do.

I don't have a service manual. Anyone have any knowledge of what a COM FAILURE message might indicate?

 

[FORANE]

maybe this guy can help?

BARNSTORMERS.COM Find Aircraft & Aircraft Parts - Airplane Sale, Jets, Helicopters, Experimental, Warbirds & Homebuilt

Aircraft for sale. Find the best new and used aircraft for sale such as business jets, helicopters, Experimental, Warbirds and more.

www.barnstormers.com

 

[Jim_R]

"Avionics Design Engineer / Event Coordinator" is an interesting combo, and also interesting that he felt it necessary/appropriate to include the EC title in his ad for avionics repair.

But like I say, I think the problem is more likely outside the radio due to the rodents, so that's where I'm going to focus first.

 

[Ryan Klems]

I kind of suspect that perhaps your coax got gnawed on. This may have resulted in a high SWR that may have cooked the power transistors for the transmit RF. The radio may either be detecting the failure of the transistors, or perhaps has detected a short or open in the coax. It's also maybe possible that the com side of the unit doesn't have power. It's been a while since I worked with an SL30, but on some avionics units that use 2 separate power inputs (like the GNS430), the nav side powers up all but the actual RF section of the COM board, so if you had power to the nav side, it might look normal (unit powers on, display functions) but gives a com failure message. The SL30 has a separate power input for the nav and com, so it might act similarly.

edit: Found the MM for the SL30, and it does sound like perhaps the com board isn't getting power, either external power not reaching unit, internal fuse is blown, etc. Still could be coax issue that then triggered high power through transistors which popped the fuse internally. But at any rate, I'd say verify power to tray on both the com and nav power inputs, and expand from there, but the problem is likely ships side from the rodent damage (though it can have then cascaded into an internal failure of the radio).

 

[Jim_R]

I kind of suspect that perhaps your coax got gnawed on. This may have resulted in a high SWR that may have cooked the power transistors for the transmit RF.

Yeah, the change in behavior over time does worry me that maybe some fault outside the box ultimately led to a failure inside the box. That's definitely a possibility.

All the more reason to try to positively exonerate all the external wiring before trying out a replacement SL30, though. I'd hate to stick a "new" (to me) unit in the tray and have it spit out all its magic smoke a few minutes later for the same reason the first one did.

 

[Jim_R]

edit: Found the MM for the SL30, and it does sound like perhaps the com board isn't getting power, either external power not reaching unit, internal fuse is blown, etc. Still could be coax issue that then triggered high power through transistors which popped the fuse internally. But at any rate, I'd say verify power to tray on both the com and nav power inputs, and expand from there, but the problem is likely ships side from the rodent damage (though it can have then cascaded into an internal failure of the radio).

Ah, those troubleshooting steps provide a very useful clue. Thanks very much for that!