Originally Posted by jliltd
It would be a great way to troubleshoot if you knew somebody with an SL40 that was willing to let you swap out the units. The conservative approach would be to try your unit in his rack and see if the same trouble comes up. If not it is probably your wiring or coax/antenna system. Be careful about transmitting with bad coax or no antenna as it can damage the radio's transmitter board circuits. Previous response here about the coax connector was aimed at the actual BNC connection on the coax itself and not the tray connector you described. Also make sure your antenna has good bonding to the aluminum skin and the coax connection there is okay. Avionics shops can test your transceiver/antenna configuration. There is also a box that can test just the coax and antenna isolated from the transceiver and no ship's power needed. But a good visual check of both ends of the coax might reveal and issue without the fuss of a tester. You could also try this known good loaner unit from your friend in your airplane but if there is something wonky in your wiring or coax you might damage the loaner so you are taking on the risk of having to replace that unit.
Also check the ground connections to the SL40 and the 403 ICS. Grounding issues can cause some weird stuff, especially when stressed such as when the comm radio is pulling extra power when transmitting.
If you put a GTR 200B in your aircraft you will not only love it, you will ditch the 403 intercom. There is no reason to keep it in the panel for any reason. Were I you I would just wire the GTR directly to the headphone jacks with new wire. Ditch all the 403 wiring. You would probably want to do this anyway because you should upgrade the headset phone wires and jacks to stereo. Plus you will want the proper service loop at the GTR location and not where the 403 used to be so the original wires could be too short or too long depending on which side of the transceiver and how far it was located. The audio signal from the GTR 200 rivals the best audio from any competitive device and warrants stereo wiring and jacks. The GTR's 3D orientation of primary and standby receive audio along with ICS seat positions is the bomb. I would be very tempted to add powered LEMO headset plugs along side the legacy headphone jacks because there is no better time than when you do this type of project. And if you have the black RG 58 coax for your antenna lead this would be a good time to replace it with RG 400 dual-shield coax.
You will not be sorry with a GTR 200B installed properly. The GTR 200B is the same height as your SL40 but that only helps not have to shift your stack. The rest of the work is basically a full install.
I have a suggestion. Why not spring for a pre-wired harness? You can still do the install. Many of the suppliers offer this for an additional charge. Stein comes to mind but ACS also does. Sound like a good plan since you seem to want to take on the project. If not then you might take it to an avionics shop.
Your SL 40 still has value on the market, whether for parts, rebuild, or if it checks out okay in your neighbor's aircraft test. I am not sure Garmin still offers repairs on the SL 40. Last year I took two DL 40 units, one with a bad faceplate and the other with a burn out capacitor on the transmit board. I swapped out the transmitter boards between them and ended up with a serviceable unit. But the SL 40s are getting older every day and have a bit of a reputation for blowing components on the circuit boards as they hit the real life mean time between failure point.
Thanks - jliltd for the great advise!
>I don't have a friend with a SL40 I can try.....Good idea.
>All comm radio wiring visual/feel and check out fine.....
>I don't see a problem with the grounds......
I would love to do/install the GTR 200B, sounds so nice:
>I would upgrade the jacks to stereo....??? - I think the new wire should be Shielded Wire, 22 Ga. 3 Conductor
>I would upgrade the antenna wire from RG58 to Rg400.....
I can't move forward until I find out the 403 and SL40 old pins to new GTR 200 plavement: Do I combine wires from the 403 and SL40 wires???
>OnSL40 I have (7) wires/pins - Power (1), TXKey (4), Mic 1 (8), Power GRN (9), RS232 input (10), RS232 GRN (11), Headphone output (14).
-I can use the power/Grn to the new GTR200
-Mic 1 - I guess Pilot PTT, but I have a pin going to the 403 also as Pilot PTT - Crimp to 403 or kill?
-Headphone - not sure what this is, but to the Pilot Headset? I also have 2 pins for Pilot Headset on the 403.
>On 403: I have (16) wires/pins: GRN(1),Pilot Mic(2),Co-Pilot Mic(3),Co-Pilot Mic(6),Pilot Mic(7),Transmit Keyline(8),Pilot HS(9),Pilot HS(10),Co-Pilot HS(11),Co-Pilot HS(12),Pilot Mic(13),Transmit Audio(17),Aux Music(18),Music Input(19),Power(20),Audio In(21)
>I think kill the power, ground....I'll use orignal power/ground to SL40.
: Transmit Keyline(8)
>I want to take-out the aux/music input/output. I'm going to use Bluetooth. So, kill (17,18,19,21)?
So - any suggestions/help would be appreciated! I'm confused on how to combine or remove wires from SL40 and 403 intercom?