Turning your SL40 into an expensive paper weight

Please no admonishments -- I'm really not in the mood this morning.

I am willing to suffer a little self-ridicule if it will save someone else a little time and money. First of all, I know virtually nothing about radios. I'm not a ham operator and I've never messed around with anything that transmits, but I've just learned what will probably be a very expensive lesson.

Take my advise on this -- do not power up your COM until you have the antenna connected. I did this and the intercom (DRE 244E) push-to-talk wires were shorted and the radio transmitted without the antenna. I didn't think it would be a big deal. Surely these radios are built for this, right? Well -- wrong. They are not. You lose your antenna off the back of your COM and try to transmit and it will fry it. I guess that's one of the many reasons why avionics manufacturers use those big right-angle coax connections -- they are critical to the life of the unit. I read the SL40 manual cover to cover and there was nothing about this in there, in spite of the fact that other elementary tidbits are there. Seems like this would have been covered. I'm not blaming Garmin at all...just seems odd something critical like that isn't covered.

Now I have the antenna connected and when I power everything up, I can pull the volume knob on my SL40 (disables squelch) and hear static...but it doesn't sound 'right' if you know what I mean. Also, twisting the volume knob has no effect. I don't have a handheld COM so it's not easy to test but I think it's hosed. The SL40 will tune the national weather service frequencies but I can't hear anything on them, in spite of the fact that my weather radio is picking up the same frequency loud and clear. I also used an old scanner and could not hear the SL40's transmissions.

Looks like I fried it...big time.

Any thoughts?

Send it back under warranty.
Good lesson. Sometimes in the excitement of wanting to see something work, we move too quickly and get bit for it. You should always work your circuits with no fuses untill its all done and you are ready to fire up and have checked the wires, pin for pin.
There are more lessons to come Jamie.
Ive never fried anything and Im sure I wont let it happen again
Best,

If transmitting with no load did damage your transeiver that is quite disappointing, because it is normal practice these days to internally protect radios from that kind of damage. Even in the old days it would most likely just blow the final/s not damage the receive section.

I AM a ham radio operator.

Different problem?

If you fried the transmitter output section by transmitting with the antenna disconnected, I wouldn't think that the receiver section would also be damaged.

If the receiver doesn't work, perhaps you have a different problem? Are you sure the antenna is good?

n5lp said:

If transmitting with no load did damage your transeiver that is quite disappointing, because it is normal practice these days to internally protect radios from that kind of damage. Even in the old days it would most likely just blow the final/s not damage the receive section.

I AM a ham radio operator.

Click to expand...

Yeah...definately sounds wierd. I'd bet that you didn't blow anything up at all and Larry's spot on that you probably wouldn't have blown up the reciever regardless. In addition, it's trivial and customary to protect the outputs these days. I'd be very surprised if Garmin doesn't do this (somebody correct me here). You might just have a dead radio out of the box.

Ditto the remarks about not damaging the receiver. Whatever you do, check the antenna (or have it checked) before you key the transmitter again. If you did damage the radio (because of a defective antenna), you might repeat this lesson.

Good luck.

Tom Costanza
RV-7A
Fuse

Ok guys...here's an update on this issue as of tonight.

I went out and triple-checked all of my wiring again. My panel is quite simple so checking all of this stuff is very straight-forward.

I double-checked continuance of the feedline center connector and shield and all is good there. I powered the radio up again and this time decided to tune the Macey arrival into ATL. It goes right down I85 directly over my house and I can walk outside my garage and usually see 5 or 6 buses with wings flying over the house. Perfect. It picked up pretty well in the garage. Loud and clear on most transmissions...and this is with the belly-mounted antenna being hidden by the fuselage. After a bit of patience I was able to hear a plane landing at nearby LZU. Hmm...seems like nothing was wrong receiving at least...so you guys were right about that fact. I also deduced that since I was receiving I was most likely not having problems with the antenna.

Then I looked at my scanner again. I haven't used this thing in ages but I remembered that there was a quirk with it (which I *hate*) which is you can't directly enter a frequency on it. You have to program a frequency to a number slot and manually choose that number. Entering the frequency and pressing enter gives the impression that you're actually monitoring that frequency when in fact you aren't.

I tuned my test frequency correctly this time and I could hear transmissions loud and clear from the SL-40.

So this left the lingering question about the volume knob being inop. The strange thing was the 'headphone level' in the setup mode would change the volume just fine, but turning the volume knob did nothing. I was up all last night re-reading the installation manual, looking for this sort of info. Nothing was there regarding this.

I *just* now decided to look at the UserGuide, which explains that setting the headphone level to 0 in the 'System Functions' mode will tie the headphone level to the volume knob! Yep...worked like a champ.

I'm gonna have my ham operator, former avionics tech, ATP-rated friend come over and work his radio voodoo on my antenna to make sure everything is up to par.

So I guess I'm a little embarrased. I think I'm going to go and hide in the corner. Kahuna...what were you saying about more lessons to be learned? Didn't know it was gonna be so soon.

The help and reassurance offered on these forums is nothing short of remarkable. Thanks, guys.

Don't feel bad. When I first installed my radio I did the same as you and thought I fried it. Every time I turned it on I got this horrible hum through the headphones. I posted on here and happened to mention that I was powering the whole rig with a battery charger. Someone responded by asking if the frequency of the hum sounded anything like 60 hertz. Huh? Suddenly the lightbulb above my head went on and reminded me that the output on a battery charger is not true dc, but rather rectified (i think) ac. Problem solved and I learned something too. Still felt like a dope though, and it wasn't the last time either.

Something else to keep in mind: The DRE244 (a great unit, BTW) does not function properly below 12.5V. If you're running on battery w/out a charger attached, and you've been using the battery for any length of time, chances are your voltage is < 12.5. I thought I had all sorts of EMI problems with my Dynon (early D-10) which turned out to be, simply, the noise cancelling electrics in the DRE not working below 12.5.

Just something to keep in mind.