Need diagnostic help

[murphey]

Configuration:
PMA 7000BT
Apollo SL 30 NAV/COM (COM 1)
TKM MX12 COM (COM 2)
Lightspeed headset.
Original 1969 era PTT

Started up the cherokee, everything fine, no problems talking to tower or ground. Took off, wandered for about 30 min then headed home.
PTT on COM 1 lots of static, even silence, I hear nothing in the headset when transmitting
I can hear everyone including tower, but I can't tell if I'm transmitting or not. Tried 4-5 times then switched to COM2.
COM2 - works fine.

Any ideas?

 

[wilkersk]

If com2 works fine, but when you're on #1 radio and depressing the PTT, and not seeing a "TX" annunciation on the display of your SL30, then it sounds like the "radio key line" on #1 radio is not seeing ground when you push the PTT. It's easy to check, just turn all power off (master switch off), pull your Audio panel out and put a meter lead on the pin labeled #1 PTT or #1 Keyline and the other meter lead to ground, then push your PTT. Your ohmmeter should read open when PTT is not push, and short when PTT is pushed.

Good chance this will turn out to be an intermittent gripe due to a failed crimp somewhere. Just moving stuff around may temporarily fix the gripe for awhile. But it'll probably eventually come back at the worst possible time.

 

[AV8R_87]

I think the diagnostic is that you're (plane) crazy.

PTT on COM 1 lots of static, even silence, I hear nothing in the headset when transmitting

As stated above, check that you have a solid TX indication on the radio and no loose connections in the PTT line from the audio panel to the radio.

My suspicion, though, is something wrong with the radio/antenna connection.
A problem there would cause the radio to stop transmitting or transmit at very low power. Radio sidetone is generated by the receiver listening to what the transmitter is sending out. So if it sounds bad, or there's no sidetone, that's what's coming out of the radio.

 

[edessa]

Also check to make sure the PMA 7000BT #1 TX is blinking when you press the PTT.
Could be as simple as a PTT button going bad.

 

[murphey]

Also check to make sure the PMA 7000BT #1 TX is blinking when you press the PTT.
Could be as simple as a PTT button going bad.

Except everything is fine on COM 2

 

[murphey]

If com2 works fine, but when you're on #1 radio and depressing the PTT, and not seeing a "TX" annunciation on the display of your SL30, then it sounds like the "radio key line" on #1 radio is not seeing ground when you push the PTT. It's easy to check, just turn all power off (master switch off), pull your Audio panel out and put a meter lead on the pin labeled #1 PTT or #1 Keyline and the other meter lead to ground, then push your PTT. Your ohmmeter should read open when PTT is not push, and short when PTT is pushed.

Good chance this will turn out to be an intermittent gripe due to a failed crimp somewhere. Just moving stuff around may temporarily fix the gripe for awhile. But it'll probably eventually come back at the worst possible time.

I do software, not hardware. Not everyone who owns an airplane knows what a meter lead to ground or an ohmmeter is and how to use it.
Not a terrible mistake, padawan, merely an incorrect assumption.

 

[wilkersk]

I do software, not hardware. Not everyone who owns an airplane knows what a meter lead to ground or an ohmmeter is and how to use it.
Not a terrible mistake, padawan, merely an incorrect assumption.

Time to find someone who does know how then.

 

[GeorgeC]

Or learn how; basic tools are very inexpensive and easy to use. There are even legends of this thing called the "internet" that was full of information, before the white man came and replaced it with increasingly short videos, and finally AI summaries that even Readers Digest wouldn't print.

 

[edessa]

Except everything is fine on COM 2

Doesn't matter. The #1 side of the audio panel could be bad just like the NAV side or the intercom part of the audio panel could be bad. Doesn't have to be the entire audio panel going bad.
It may be time to talk to an avionics tech.

 

[WDD]

Have you done a radio check on Com 1? That is, even though you can't hear yourself when you try to transmit on Com 1, can others hear you?

 

[asicer]

Do you have a handheld with which you can talk with yourself?

 

[murphey]

Time to find someone who does know how then.

Why is "get the tools, learn how" is far too often the answer around here.
I'm a reasonably good practitioner (candidly, I'm really, really good according to my employers before I quit) in my field. Even getting the tools and minimal training, I'll never be good enough to evaluate the results of the ohmeter. Nor do I ever expect anyone who took the online Dummies for Software to ever come near my level of expertise.

Do you have a handheld with which you can talk with yourself?

handheld check this weekend…

 

[WDD]

Nothing wrong with a plane owner paying for someone who knows what they are doing do the work.

If a plane owner has tools, time, and a knack for wrenching, great. Some have it more than others. All good whatever level.

 

[asicer]

handheld check this weekend…

Don't forget the Allen keys for reseating the boxes.

 

[GeorgeC]

Why is "get the tools, learn how" is far too often the answer around here.
I'm a reasonably good practitioner (candidly, I'm really, really good according to my employers before I quit) in my field. Even getting the tools and minimal training, I'll never be good enough to evaluate the results of the ohmeter. Nor do I ever expect anyone who took the online Dummies for Software to ever come near my level of expertise.

I'm a software guy too. I'm careful to avoid Dunning-Krugering myself when it comes to anything but software, especially airplane diagnostics. On the other hand, in my experience, the "Jesus, take the wheel" approach to aircraft maintenance and expecting your mechanic(s) to find and correct every nit is not a winning strategy. Example: earlier this year, one of my tailwheel steering springs popped off during landing. It turned out the tension was nowhere near spec, only revealed after I went digging to RTFM. This was after annuals at 5 different shops... You are PIC and it's your ass (and that of your pax) that's on the line.

 

[WDD]

Excellent point. You can still have the A&P do the work, but you're responsible for the airplane. You're not supposed to be the "maintenance passenger" being directed by the mechanic, but the active owner directing the A&P. You can direct the mechanic to look at things you can't get at or don't have the experience to know what you're looking at, make the decision on what needs to be done, and act accordingly. (I think I stole some of this from a Mike Busch video).

I'm not a doctor who knows how to operate, but if I have this thing and I go to my doctor and she says "don't worry about it", I'm getting a second opinion to corroborate or disprove the initial diagnosis and make the decision on the course of action.

 

[Tools]

My guess is antenna. Some water or moisture gets where it wasn’t, a thing called impedance and SWR go all awry and it won’t transmit. May or may not be able to listen.

Could be lots other, but that’s a good place to start.

 

[MauleSkinner]

Why is "get the tools, learn how" is far too often the answer around here.

Im not going to speculate on “far too often,” but in this specific case it probably has to do with the fact that you asked for “diagnostic help,” and the tools in question are diagnostic tools.

 

[JOhnH]

Nothing wrong with a plane owner paying for someone who knows what they are doing do the work.

If a plane owner has tools, time, and a knack for wrenching, great. Some have it more than others. All good whatever level.

I have a knack for wrenching. It's just not good enough for me to trust myself working on my airplane when a mistake could kill me and others.
That's why I don't think A&Ps make enough money and I only complained about a charge once. And that was because it was a charge that should have gone to someone else's plane.