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Topic Options
#155180 - 11/17/13 12:43 AM Rt-359a Transponder
Birdman Offline
Bronze Pilot

Registered: 07/06/12
Posts: 667
Loc: Woodland, CA, USA
Went out to fly today and the # 2 radio and transponder would not turn on. After a little jostling the radio came on but not the transponder. Dirty contacts? Seems strange that both the radio and the transponder would have dirty contacts at the same time. I was thinking of pulling the transponder, cleaning the contacts and seeing if it will power up. I know that I can not legally re-install the transponder but I am expecting my technician next week anyway.

My question is how to remove the transponder. There is a screw through a hole in the front to release it but I have seen some radios that unscrew out and some that have a cam type lock that only require a quarter turn. It is unclear which this one is. It is a 300 XPDR, rt-359a. I don't have a manual. I would like to know before I start tugging on stuff.

Any advice would be appreciated.

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#155213 - 11/17/13 05:21 AM Re: Rt-359a Transponder [Re: Birdman]
LV-CWK Offline
Safety Pilot

Registered: 09/28/12
Posts: 29
Loc: Buenos Aires, Argentina
Hi, here is a link to the xponder removal info and also to the first checks you can do yourself:

http://transponderrepair.com/HelpMain.htm

Here you have another link to the pinout in case you want to check wiring and power...

http://www.texasairsalvage.com/PinnoutPDFfiles/RT359A_459A_859A.pdf

I would first check power with a tester and a faulty fuse...

Good luck
Mario

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#155217 - 11/17/13 05:53 AM Re: Rt-359a Transponder [Re: LV-CWK]
Luvrv8 Offline
Gold Pilot

Registered: 03/12/10
Posts: 1024
Loc: Camarillo, Ca
The first link to the transponder repair shop is a shop I have used and recommended to a few friends. Up front pricing and good work, none of us had problems after the repairs.
_________________________
1967 172H 2641L. It isn't much but it's paid for and all mine.

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#155236 - 11/17/13 02:36 PM Re: Rt-359a Transponder [Re: Luvrv8]
vettdvr Offline
Club Sponsor
Diamond Pilot

Registered: 06/25/10
Posts: 7724
Loc: Slidell La
Yes from the way I understand the regs, you can remove the transponder. Mine has a hex screw in the open hole in the case. Back out the hex and it should pull out. You should be able to remove and install a plug in device. You can not open or attempt to work on it. You can however check plugs/pins to see if they are clean and look for loose plugs in the rack or dirty pins inside. A long Q tip with alcohol might be used to clean the rack plug pins.
_________________________
Vettdvr

Single/Multi/instrument/type/commercial But then I am still learning.

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#155264 - 11/17/13 05:09 PM Re: Rt-359a Transponder [Re: vettdvr]
Luvrv8 Offline
Gold Pilot

Registered: 03/12/10
Posts: 1024
Loc: Camarillo, Ca
Vettdvr is correct.
_________________________
1967 172H 2641L. It isn't much but it's paid for and all mine.

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#155278 - 11/17/13 06:08 PM Re: Rt-359a Transponder [Re: Luvrv8]
Birdman Offline
Bronze Pilot

Registered: 07/06/12
Posts: 667
Loc: Woodland, CA, USA
Thanks for the great information. Exactly what I was looking for. I suspect I have a power supply problem as initially both the radio and transponder did not come on. The confounding thing is why the radio eventually did come on and the transponder did not. Sounds like am electrical gremlin of some sort which can be the worst thing to locate.

It is my understanding that removing and replacing the transponder needs to be done under the supervision of a licensed mechanic. I was planning on doing this once on my C150 and was told I could not do it by myself. On the link supplied by LV-CWK on the top of the "Airframe Issues" page the first paragraph would lead one to believe that. Also on the link to FAR 43 appendix A way at the bottom of the page defining "Preventative Maintenance" number 31 excludes removing and replacing transponders. Am I interpreting this incorrectly? I would love to be wrong about this.

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#155291 - 11/17/13 07:46 PM Re: Rt-359a Transponder [Re: Birdman]
vettdvr Offline
Club Sponsor
Diamond Pilot

Registered: 06/25/10
Posts: 7724
Loc: Slidell La
If your transponder is a plug in rack with front hex screw it would fall under removing radios (it is a radio that transmits) you should be able to remove it yourself. Just you can't open it to work on it. You can take it to a shop minus the plane and have it checked out and repaired if necessary. Then plug it in.

But feel free to have a AP monitor if you chose.

There is a used one on Ebay now for a little over $100 doesn't mean it met reserve but they are available use.


Edited by vettdvr (11/17/13 07:50 PM)
_________________________
Vettdvr

Single/Multi/instrument/type/commercial But then I am still learning.

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#155294 - 11/17/13 07:58 PM Re: Rt-359a Transponder [Re: vettdvr]
Birdman Offline
Bronze Pilot

Registered: 07/06/12
Posts: 667
Loc: Woodland, CA, USA
Thanks vettdvr. Mine is a slot head screw but it serves the same purpose of holding/locking the transponder in place.

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#155493 - 11/18/13 05:37 PM Re: Rt-359a Transponder [Re: Birdman]
LV-CWK Offline
Safety Pilot

Registered: 09/28/12
Posts: 29
Loc: Buenos Aires, Argentina
Hi again,

The xponder is one of the simpliest avionics, theres no risk in removing it from the tray, check for dirt/loose contacts, check power at the corresponding pin (master on, positive tester lead at connector pin, negative tester lead at a/c frame) and reinstall the xponder in place. Make sure it goes all the way in and its completely locked with the screw to ensure proper RF (antenna) connection, and if its a mode C check for proper connection to the external altitude encoder after reinstallation.

On the first link youll find a lot of accurate help on doing all these tests.

If the xponder doesnt apparently turn on get your ear close to it anand check for the high pitch sound, if it sounds the xponder is working and it may be the blown lamp inside the button. If it comes on and off intermitently its more likely to be a lose contact in the power line to the equipment, check for a lose terminal on the power bus and inline fuses/connections other than the breakers.

Regards
Mario

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#155498 - 11/18/13 06:38 PM Re: Rt-359a Transponder [Re: LV-CWK]
Birdman Offline
Bronze Pilot

Registered: 07/06/12
Posts: 667
Loc: Woodland, CA, USA
Thanks Mario. I did remove the transponder yesterday following the instructions on the link you sent me. I cleaned the pins although they did not look dirty. There is no response at all from the transponder. No high pitch whine, no lights with the dimmer knob turned up etc. The circuit breakers look normal and I did find a couple of inline fuses behind the panel that I am not sure what they are connected to but I checked them and they appear to be ok.

So my guess there is a problem with power. Unfortunately I don't know much about electrical matters. My next step is to check to see of voltage is getting to the harness. I do have a multi tester and wanted to test for current. As I understand your post I put the red positive probe in the pin receptacle that brings power to the unit and ground the black negative probe. In this case it is pin 22 and they are clearly marked on the harness.

When I took out the transponder something was rattling around inside. Doesn't give you a high degree of confidence. A plastic part dropped out that looked like it would secure a cable. Not sure if it is part of the transponder or fell in the back from something else.

Thanks for your help.

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#155586 - 11/19/13 01:56 AM Re: Rt-359a Transponder [Re: Birdman]
Birdman Offline
Bronze Pilot

Registered: 07/06/12
Posts: 667
Loc: Woodland, CA, USA
Progress report: So checked for power to the harness and it check out fine. I also checked for conductivity from pin 23 to pin 8 for the jumper, that looked good too. The pin out diagram also shows 2 pins for ground, numbers 1 and 2. Pin 1 has a larger gauge wire to it and it checked out fine. Pin 2 has one of the small gauge wires to it and I got sporadic or no response on the ohm meter. This could be the problem. I don't know why there would be 2 grounds however.

Before I start tearing apart wire bundles to trace where that wire leads however I will try to see if I can have the transponder bench tested to make sure it comes on with a known good power and ground source. The guy that certifies a lot of the transponders in our area is supposed to be out our way at the end of the week and I hope he might be able to help me out with this.

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#155695 - 11/19/13 08:38 AM Re: Rt-359a Transponder [Re: Birdman]
LV-CWK Offline
Safety Pilot

Registered: 09/28/12
Posts: 29
Loc: Buenos Aires, Argentina
Hi Birdman,

Does your COM work now? have you found why it didnt work before? As per your comments theres a faulty contact on the COM too... Maybe both the COM and the xponder are connected to the same power source/breaker/fuse. Make sure you have continuous power on both units no matter if you shake the cables or trays. If the COM worked intermitently theres a connection calling to be tightened/re-soldered/cleaned...

If power is ok and theres no high pitched sound from the xponder it its probably the internal power supply circuitry, just send the xponder for a bench test, but regardless of this make sure all avionics connections are secured and theres no faulty contacts to avoid malfunctions while flying...

Good luck & regards
Mario


Edited by LV-CWK (11/19/13 08:39 AM)

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#155734 - 11/19/13 04:59 PM Re: Rt-359a Transponder [Re: LV-CWK]
Birdman Offline
Bronze Pilot

Registered: 07/06/12
Posts: 667
Loc: Woodland, CA, USA
Hi Mario:

The Com seems to work now. It has come on every time I have turned it on since but that doesn't mean that all is perfect. I will try to trace back the wires but that is not easy in the "birds nest" of wires under the panel. That radio has always been very scratchy and I basically only use it to listen to atis, Awos etc. I want to try cleaning the contacts and see what that does.

There is a highly regarded avionics shop in Sacramento I have used before that I can take the transponder to and get a diagnostic on pretty quickly. I am planning to do that today.

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#155750 - 11/19/13 07:12 PM Re: Rt-359a Transponder [Re: Birdman]
vettdvr Offline
Club Sponsor
Diamond Pilot

Registered: 06/25/10
Posts: 7724
Loc: Slidell La
Is it possible the transponder is defective loading the circuit preventing the com from working? Before you pull any wire bundle I think you are correct in having the Transponder tested.
_________________________
Vettdvr

Single/Multi/instrument/type/commercial But then I am still learning.

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#155751 - 11/19/13 07:16 PM Re: Rt-359a Transponder [Re: vettdvr]
Teg916 Offline
Bronze Pilot

Registered: 04/30/13
Posts: 675
Loc: Sacramento, ca
From what you are describing I would highly suspect the ground is causing your radio issue as well as the transponder. It is likely they are both grounded at the same location. It could be something as simple as a dirty ground, or a loose nut at a grounding terminal.

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#155752 - 11/19/13 07:33 PM Re: Rt-359a Transponder [Re: vettdvr]
LV-CWK Offline
Safety Pilot

Registered: 09/28/12
Posts: 29
Loc: Buenos Aires, Argentina
I agree vettdvr.

At this stage better get the xponder tested first, reinstall, and recheck for intermitencies...

Regarding power ground bear in mind these are not floating ground radios, their chassis are connected directly to the power supply circuitry, so as far as they are on their trays they should have power ground available. Theres a specific wire dedicated for power ground as thats the right way to provide enough power current and a make a reliable connection to ground, but as per Bridmanīs comments he has also checked this.

Keep us posted Birdman.


Edited by LV-CWK (11/19/13 07:35 PM)

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#155785 - 11/19/13 11:06 PM Re: Rt-359a Transponder [Re: LV-CWK]
Birdman Offline
Bronze Pilot

Registered: 07/06/12
Posts: 667
Loc: Woodland, CA, USA
Just back from the avionics shop. The problem was a an internal fuse that had gone bad. It was not blown, it was a mechanical failure from years of vibration as it was explained to me. The good news is it was fixed in 10 minutes for $20.

The transponder technician I spoke with on the phone last night made the same point that LV-CWK made regarding grounding in that the radios are in racks attached to the frame. He said that he would be surprised if grounding was the problem.

I'll clean the contacts on the Com and see how it goes. Thanks to everyone for all the help.

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#155802 - 11/20/13 12:42 AM Re: Rt-359a Transponder [Re: Birdman]
vettdvr Offline
Club Sponsor
Diamond Pilot

Registered: 06/25/10
Posts: 7724
Loc: Slidell La
$20.. be sure to get the log book signed off for the fuse replacement.
_________________________
Vettdvr

Single/Multi/instrument/type/commercial But then I am still learning.

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#155869 - 11/20/13 06:39 AM Re: Rt-359a Transponder [Re: Birdman]
LV-CWK Offline
Safety Pilot

Registered: 09/28/12
Posts: 29
Loc: Buenos Aires, Argentina
Glad to hear that Birdman!

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#155878 - 11/20/13 07:53 AM Re: Rt-359a Transponder [Re: LV-CWK]
Teg916 Offline
Bronze Pilot

Registered: 04/30/13
Posts: 675
Loc: Sacramento, ca
Glad you got her fixed!

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