GTX327 Oddity

logansc · #1 10-05-2011, 01:24 PM

Think I asked this one before, but didn't get a definitive answer. My transponder comes on at aircraft power up (master switch on) but will not turn off after that unless the master is turned off. It starts up in 'Standby' and can be switched either "On" or "Alt" with the switches on its face. Alternatively, it will turn on after liftoff per the "airborne sensor" feature.

What it won't do is go back to "On" only, once "Alt" has been selected, nor to "Stanby" once "On" has been selected, nor "Off" once "On" has been selected. I've been through my installation manual fairly carefully, but so far I haven't found a reference (that I understand, at least) to why it is acting this way.

Any help appreciated.

Thanks,

Lee...

erich weaver · #2 10-05-2011, 01:37 PM

Its been years, but this sounds very familiar. I seem to recall its all in the way the harness is wired. I had mine done by Stark Avionics, but after running into similar issues, had to redo one or two pins on the d-sub connection to get the power to function the way I wanted it to . Not sure if the full answer is in the archives here or on the Matronics Aeroelectric forum. Kinda busy or I would search for it myself, but this should give you hope and a place to look.

regards
erich

etekberg · #3 10-05-2011, 01:57 PM

I'm a little unclear understanding the problem from your description. Is the problem that you can't use the buttons to turn it off? Also, what software version do you have installed?

Bill Dicus · #4 10-05-2011, 02:01 PM

I have a GTX-330 which also turned on with master on (power applied to radio). My manual also says the radio should not be subjected to electrical transients associated with engine start! Disconnecting a jumper at pin #1 (per my installation manual I believe) disables the automatic turn-on feature. Don't know about the inability to turn off- have you checked configuration options and/or called Garmin? Good luck.

etekberg · #5 10-05-2011, 02:13 PM

On mine, if you want it to turn off, you have to hold the off button for a few seconds. I have an older software version, however. Standby should just be a one button push. If you can't turn it off without removing power, I would suspect a problem with the unit that would need to be corrected by either a software upgrade, or a trip to Garmin.

The automatic turn on is a wiring feature as described and is typically used in conjunction with an avionics master switch, not just a battery master switch.

logansc · #6 10-05-2011, 09:36 PM

Yes, it's that it won't turn off with the buttons. I'm aware the manual says it should be off for engine start, but it doesn't work that way! When the battery switch goes on, the GTX-327 comes on in Standby. Won't turn off unless I turn the battery/alternator switch off. Once I switch to On or Alt just prior to takeoff, it won't go back to Standby nor to Off no matter how long I hold the Off or Standby switch.

I'll check which software, but I'm pretty sure it's a wiring issue, just don't know which wire. Thanks for the inputs.

Lee...

rleffler · #7 10-06-2011, 04:27 AM

Quote:

Originally Posted by logansc

Yes, it's that it won't turn off with the buttons. I'm aware the manual says it should be off for engine start, but it doesn't work that way! When the battery switch goes on, the GTX-327 comes on in Standby. Won't turn off unless I turn the battery/alternator switch off. Once I switch to On or Alt just prior to takeoff, it won't go back to Standby nor to Off no matter how long I hold the Off or Standby switch.

I'll check which software, but I'm pretty sure it's a wiring issue, just don't know which wire. Thanks for the inputs.

Lee...

There is a wire, if connected to the avionics master (or any other voltage source) will automatically turn the transponder on. I have VP-X, so I didn't need this feature. With that said, I didn't think that would prevent you from turning the unit off.

PM me if you need the installation manual.

bob

rzbill · #8 10-06-2011, 09:22 AM

That would be pin #1

It is noted as "Avionics Master On" in the 327 manual.

It is NOT the power feed, that is pin 15.

Refer to the install manual for more detail.

logansc · #9 10-06-2011, 01:23 PM

Thanks everyone, I'll check it out. I'm guessing that if I have a feed to pin #1, the 327 won't turn off because pin 1 is continually telling it to stay on.

Regards,

Lee...

etekberg · #10 10-07-2011, 07:46 AM

Quote:

Originally Posted by logansc

Thanks everyone, I'll check it out. I'm guessing that if I have a feed to pin #1, the 327 won't turn off because pin 1 is continually telling it to stay on.

No. It should still turn off. I don't think it's a wiring problem.

The "typical" installation has pin #1 ("AVIONICS MASTER ON") wired to the pin #15 (POWER INPUT (14/28V DC)). Mine is wired that way, but I have an avionics master switch. Mine turns off when I hold the off button for several seconds.

I think you have two issues.

1) I think you have a problem with your unit that needs a repair.
2) Since you don't have an avionics master switch you probably want to cut the wire going to pin #1 and put some heat shrink tubing on it to insulate it, since it carries power. You will then have to press the on button every time you start up.