Head Scratcher - VOR G/S problem

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netconn
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Head Scratcher - VOR G/S problem

Post by netconn »

On a M5-235 I bought a year ago, I have been chasing this problem down for months and still can't find the cause... I have a KX155, Century HSI & converter and switcher (GPS/VOR). The GPS (250XL) indicates just fine but the VOR is not working..
I've swapped the antenna (the code is loud and clear), I've swapped the 155 (tested mine in another plane, works fine), swapped the converter, swapped the diplexer and bussed the switcher... Can't find anything wrong..
I have a test set for VOR, LOC and G/S that transmits the test signals from inside the plane. They make the VOR, LOC and G/S work fine (flags and needles move as expected), but the VOR, LOC and G/S (while flying) does nothing.
Yesterday I flew to Twin Falls, there's a VOR right off the side of the runway.. Good place to try and test it while landing. Nothing!!... While parked on the tarmac I turned on the radios to see if it would do anything, the VOR worked fine..... So I'm thinking maybe the antenna IS bad (even thought I bussed it and tried another antenna... Then we go to leave, I started the plane and the VOR didn't work anymore, taxied and took off right next to the VOR, nothing!! Now I'm thinking it has something to do with the engine running but there's no radio noise or Alt whine and all the other avionics work fine.
Anyone ever see something like this? Anyone have any ideas what to look for. I'm very experienced in avionics and I'm an IA but this is a new one on me. Time to ask the brain trust....

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Andy Young
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Re: Head Scratcher - VOR G/S problem

Post by Andy Young »

That IS a weird one. First thought (and I’ll try to ponder it more later; busy day) is that when I’ve had weird electrical problems, it’s quite often a deficiency on the ground side somewhere.

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Andy Young
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Re: Head Scratcher - VOR G/S problem

Post by Andy Young »

No epiphanies came to me overnight. As a diagnostic strategy, you might try turning off the alternator switch while the engine is running to see if that brings any change.

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Jon
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Re: Head Scratcher - VOR G/S problem

Post by Jon »

Is working or not correlated with the engine running? What's the condition of the coax cable and connectors between the nav/comm and the antenna? Where is the antenna mounted? If it has a separate ground plane, what's its condition?

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