This is reaching out to a very special someone(s) out there that likes reading schematics and can see what I've done wrong. Only the brave and willing need read on. First some background.
I have just installed a second COM (MGL V16) and a PMA8000B Audio Panel, along with a NAV radio (MGL N16) and control head (MGL Razor). I moved the existing GTR200 as well. I designed and built all of the wiring harnesses - the GTR harness is adapted from the factory supplied harness. There were other changes to unrelated systems that I'll detail in a moment. Most everything works as expected. I have 2 snags.
1. Noise. I've got a fair amount of new noise in my headset, from master switch on onward. Gets worse when I power on the avionics (including both COMs and the Audio Panel), but not appreciably when I power on individual items.
2. This is the show stopper. I show a Pilot PTT Stuck full time on the GTR200 (COM1). This comes from the Audio Panel, so not an actual stuck PTT. Doesn't matter if I transmit on COM1 or COM2.
I've triple checked most everything, my actual wiring is decent, all connections that I intended to make are correct. You can see the as built schematic for the Audio Panel harness where I've also added the COM1 and COM2 harnesses. I use shielded 2 and 3 conductor cable, shields are terminated to ground at the audio panel only. Shield ground is passed through the Molex connectors.
For troubleshooting the stuck PTT, I've tried quite a few things.
- verified that I don't actually have a stuck PTT.
- used multimeter to check the PTT connectors in my harness to see if anything is grounded. I found that the PTT pin on the COM1 connector is grounded when the system is powered up, but not otherwise.
- I swapped COM1 and COM2 connections, the problem went away on the GTR and didn't appear on the V16
As you can see from my drawing, I've wired TX Interlock. In updating the drawing I saw one thing that may be an issue, but I don't see why. The V16 connector joins audio in ground to pilot PTT. I believe I have this wrong, but I don't see how this would cause issues with PTT on the other radio. I also used a possibly incorrect ground pin on the V16 for the pilot mic, but again, don't see how that would affect the other radio.
If you are still reading, you are awesome and I thank you.
If you are observant, you will see that I don't wire a mic lo. I rely on the PTT itself to provide the lo. I can't find where I got this from, but it wasn't my idea. Maybe it's an issue.
I think that covers my issue. If you can decipher my drawing and see something I did wrong, I would be so appreciative.
As promised above, here is a list of all of the changes that I did at the same time as this upgrade.
- created a secondary avionics buss running off of a 15A circuit on my VP-X. This is switched on with my avionics master and feeds 4 traditional circuit breaker protected circuits. COM2 (V16) and Audio Panel are each one of these circuits.
- installed N16 and Razor
- installed Delta Pop Aviation VHF antenna under left wing for COM2
- installed Bob Archer NAV antenna in left wingtip
- some physical relocation of panel items
- new radio rack with space ready for my GPS175 which should arrive in a couple of weeks.
- replaced my keyed ignition switch with a pair of magneto toggles and a start push button
- access panel installation - this is the only thing I'm really sure has nothing to do with my issue.
There, that's it. Thanks for getting this far. I'd love to get this wrapped up before long. I'm missing on some really nice flying weather and the constant head scratching is leaving a divot.
I have just installed a second COM (MGL V16) and a PMA8000B Audio Panel, along with a NAV radio (MGL N16) and control head (MGL Razor). I moved the existing GTR200 as well. I designed and built all of the wiring harnesses - the GTR harness is adapted from the factory supplied harness. There were other changes to unrelated systems that I'll detail in a moment. Most everything works as expected. I have 2 snags.
1. Noise. I've got a fair amount of new noise in my headset, from master switch on onward. Gets worse when I power on the avionics (including both COMs and the Audio Panel), but not appreciably when I power on individual items.
2. This is the show stopper. I show a Pilot PTT Stuck full time on the GTR200 (COM1). This comes from the Audio Panel, so not an actual stuck PTT. Doesn't matter if I transmit on COM1 or COM2.
I've triple checked most everything, my actual wiring is decent, all connections that I intended to make are correct. You can see the as built schematic for the Audio Panel harness where I've also added the COM1 and COM2 harnesses. I use shielded 2 and 3 conductor cable, shields are terminated to ground at the audio panel only. Shield ground is passed through the Molex connectors.
For troubleshooting the stuck PTT, I've tried quite a few things.
- verified that I don't actually have a stuck PTT.
- used multimeter to check the PTT connectors in my harness to see if anything is grounded. I found that the PTT pin on the COM1 connector is grounded when the system is powered up, but not otherwise.
- I swapped COM1 and COM2 connections, the problem went away on the GTR and didn't appear on the V16
As you can see from my drawing, I've wired TX Interlock. In updating the drawing I saw one thing that may be an issue, but I don't see why. The V16 connector joins audio in ground to pilot PTT. I believe I have this wrong, but I don't see how this would cause issues with PTT on the other radio. I also used a possibly incorrect ground pin on the V16 for the pilot mic, but again, don't see how that would affect the other radio.
If you are still reading, you are awesome and I thank you.
If you are observant, you will see that I don't wire a mic lo. I rely on the PTT itself to provide the lo. I can't find where I got this from, but it wasn't my idea. Maybe it's an issue.
I think that covers my issue. If you can decipher my drawing and see something I did wrong, I would be so appreciative.
As promised above, here is a list of all of the changes that I did at the same time as this upgrade.
- created a secondary avionics buss running off of a 15A circuit on my VP-X. This is switched on with my avionics master and feeds 4 traditional circuit breaker protected circuits. COM2 (V16) and Audio Panel are each one of these circuits.
- installed N16 and Razor
- installed Delta Pop Aviation VHF antenna under left wing for COM2
- installed Bob Archer NAV antenna in left wingtip
- some physical relocation of panel items
- new radio rack with space ready for my GPS175 which should arrive in a couple of weeks.
- replaced my keyed ignition switch with a pair of magneto toggles and a start push button
- access panel installation - this is the only thing I'm really sure has nothing to do with my issue.
There, that's it. Thanks for getting this far. I'd love to get this wrapped up before long. I'm missing on some really nice flying weather and the constant head scratching is leaving a divot.