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VOR Troubleshooting - 30 Degrees Off


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All,

I bought my Mooney C about 4 months ago and unfortunately the previous owner only flew it about 10 hrs/yr for the last few years and I'm finding squawks that weren't there on the pre-buy. One of the main ones is the VOR is indicating about 30 degrees off. I did some asking at Oshkosh but unfortunately the salesman to knowledgeable professional ratio was grossly out of proportion that day. The Garmin guy was certain I needed to buy a new GTN650 to fix the problem.

Here's the facts:

1. I have a non-WAAS 430 with a cat whisker antenna and Collins VOR with GS.  

2. I receive IDENT and the TO or FROM flags when I tune to a VOR. It appears to work except for the OBS being off by 30 degrees.

3. GPS indications and ILS with glide slope works.

Any thoughts? The fact that everything works except for the OBS being off makes me think it's the VOR instrument itself because the GPS and ILS don't care what the OBS says. But I'm not sure if that's repairable, programmable or if I need a new instrument. I remember this happening to a newer 172 I used to rent but can't remember the outcome or what they did to fix it. Despite the Garmin reps prodding, pretty sure I don't need a new GTN650.... or do it..... : )

Helpful inputs appreciated.

Nate

 

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Nate,

unless you ask your PPI to cover the nav equipment, it probably won't get done.  That would typically involve a couple of hours of flying time to exercise a complete array of radios...

There is no standard for PPIs for what gets covered.  

See your local radio shop.  They have the equipment to test and adjust for issues like this.

Try to clear up what radio is attached to which display.  And which antenna goes to what radio...some antennae can be shared by multiple radios.  Some are stand-alone devices.

Make a chart and use the wiring diagrams.  It's the homework that the radio shop will benefit by having instead of having to going looking for it...

The Garmin radio has a few functions with matching antennae

1) comm

2) GPS nav

3) VOR

4) ILS

Some airports (used to) have a VOT.  A VOR test facility, nice for testing your VOR while on the ground..?

some things to look for that is 'normal' for planes that go unused...  Checking and cleaning the connections of antennae and all the radios may be helpful. A small amount of oxidation can keep a pin from working...

If you have the manuals for your radios, it will make it easier to identify all the antennae.  If you don't, Garmin probably has a good website to go to..?

This is PP experience.  I'm not an instrument guy...

Best regards,

-a-

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6 hours ago, MooneyNate said:

All,

I bought my Mooney C about 4 months ago and unfortunately the previous owner only flew it about 10 hrs/yr for the last few years and I'm finding squawks that weren't there on the pre-buy. 

 

Ha, that's what happened to me too. 

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One antenna 4 functions.  2 GS and 2 NAV.    There is probably a splitter or 2  behind the radios.  My splitter is located on the cage tubing under the Pilot access cover.  The splitter should be within 12 inches of the radio stack.  Since you are getting one to work, it is probably not the antenna.  It sounds like it would be the one device that is not working.

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On ‎8‎/‎12‎/‎2016 at 5:51 PM, Yetti said:

One antenna 4 functions.  2 GS and 2 NAV.    There is probably a splitter or 2  behind the radios.  My splitter is located on the cage tubing under the Pilot access cover.  The splitter should be within 12 inches of the radio stack.  Since you are getting one to work, it is probably not the antenna.  It sounds like it would be the one device that is not working.

You could be right and hopefully that's all it is. I've read a few articles online about troubleshooting the Nav/Comm and both mentioned the splitter. I'll let you know what I find out.

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I am unfamiliar with the collins Nav radio and indicator workings.  I recently had the exact symptoms in my KI-209 / KX-170B setup, so I'll share. 

In my case the Nav radio delivers a signal to the indicator and the indicator does the decoding.  Because it was receiving the GS/LOC fine, the radio itself was working correctly. 

The problem was traced to a dirty POT in the KI-209.   Cleaned and the indicator is working properly. 

Buyer beware it may be more cost-effective in the long term to invest in new equipment rather than throwing money at a recurring problem.  That will be for you to decide.

I was charged 1 hr to R&R the indicator, 4 hrs of bench time.  Remember that avionics shops charge 80-100/hr.  That's a significant investment in very old equipment, but it's backup for me and I wanted it working, so I bought myself another several years, hopefully.  Fortunately, my KI-209 is compatible with modern GPSs, so when it comes time to replace the 170B, the indicator may be reused. 

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the #2 CDI in my plane when I bought it was off about 12 degrees... It was an older narco cdi that had a tiny graphite washer holding the OBS card.. I was advised that some of the old units that had this would allow the card to slip out of alignment and the washer is so brittle that fixing it is unlikely as new parts aren't easily available.  I bought a used KI-208 for $200, which required new plug termination and the problem was solved.

I would check the contacts as bradp suggested, but I would bench test the Nav radio before thinking about getting a new CDI.  repairing old nav heads seems to be sketchy.

 

 

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Both of my NAVs are off...#1 by 30 degrees and #2 by 17 degrees.  The units are fed from a KX-165 (#1) and KX-155 (#2).  The #1 has been off course for 15 years despite two attempts by a local avionics shop to center it via the radio box "tuning" screw on the bottom (or top?) of the box.  The #2 worked flawlessly and was dead accurate until last month when it drifted off.  Had the local avionics tech center it via the KI-208....but it promptly went out again on the very next flight.

So I called Bevan-Radell today....learned that the #1 NAV problem is likely a problem in the radio itself and needs to be opened up and checked.  But for the KX-155, the tech said the problem is likely in the KI-208 itself since it can't resolve the signal properly.  (Basically, either the KX-155 works or dies...no "in between" usually is what I gathered from him.)  So both units are off to Wichita for repair.  Much cheaper than replacement with new devices...

 

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Nate it appears that one of the goniometer wires in the CDI is either disconnected or not making contact. Remove the VOR receiver from it's tray and spray contact cleaner on the unit and the tray. Do the same with the CDI indicator. Check that all the wires are attached to the connectors.

José  

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I had this exact same problem when I bought my Avidyne 440s and I vaguely remember a similar issue on a 530 years ago I used. But times it ended up being a simple adjustment of the settings in the boxes themselves. Big relief. I think you just need the installation manual to do it. If I remembered how to do it I'd write you the directions but I don't and I don't have an install manual handy but look into the settings in the 430 for the CDI needle.

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  • 2 months later...
On ‎8‎/‎19‎/‎2016 at 7:18 AM, NotarPilot said:

I had this exact same problem when I bought my Avidyne 440s and I vaguely remember a similar issue on a 530 years ago I used. But times it ended up being a simple adjustment of the settings in the boxes themselves. Big relief. I think you just need the installation manual to do it. If I remembered how to do it I'd write you the directions but I don't and I don't have an install manual handy but look into the settings in the 430 for the CDI needle.

I realize this was a few months ago but thankfully this is what it was. If you hold "enter" down as the 430 (or 530) boots up, and release it once you get to the test screen, it puts you in the set-up mode. From there you click right through pages and (what seems like forever) you get to the OBS settings page. From there you calibrate the OBS to 150 degrees. I appreciate the advice!

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