GNS-530W NAVCOM Troubleshooting

[jaylw314]

15 hours ago, FLYFST said:

One curious and concerning thing is that when using NAV-1, the GNS will ID the station and display the radial and distance. When in the VLOC mode the GNS is driving the HSI and that shows the proper to/from indication, the NAV flag does not show, all of which indicates proper Nav performance. BUT, when far from the station I do not receive the audio ID and without it present

Just hope I'm not beating the obvious drum here, but you do press the NAV volume knob to turn off the squelch when you listen to it, right?  "ID" should appear above your NAV frequencies.  Otherwise, you won't hear it unless you're REALLY close to the station...

[FLYFST]

great pics, Hank!
 
What are the lines on the blade antenna?
Is that just dirt on the plastic tape?
Or is the tape holding it together?

The lines show were the plastic cover started to delaminate from the antenna soon after I bought the airplane. I put the tape around the leading edge to prevent further delamination, which it did and I did not note a performance issue back then. I have not changed the tape in over six years. Swapping the coax at the diplexer output to the radios in the cockpit only improved the NAV-1 performance marginally and did not make the NAV-2 performance worse, so I don’t think the antenna is the issue.

As my troubleshooting continues, the evidence pointing to a weak NAVCOM in the GNS530 appears to be growing. The Garmin refurbish price is now $1,850.


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[FLYFST]

Just hope I'm not beating the obvious drum here, but you do press the NAV volume knob to turn off the squelch when you listen to it, right?  "ID" should appear above your NAV frequencies.  Otherwise, you won't hear it unless you're REALLY close to the station...

Correct. The GNS actually identifies and displays the primary station ID, radial and distance. When I listen for the audio ID, I press the NAV volume and see the ID indicator. But while I receive the audio on NAV-2, I don’t receive it on NAV-1 at the same frequency until I am closer to the station, even though the GNS530 has the station identified and is sending NAV signals to the HSI, which appears to be operating normally. However, the apparently correct NAV indications on the HSI are unreliable until I start receiving the audio for the station ID.

Some of the above is from memory recall and requires that I fly a more detailed set of tests and take better, more detailed notes to make sure what I recall is correct.


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[FLYFST]

Update on the troubleshooting: I had the GNS-530W bench tested and found no issues of concern.  The NAV radio was just a little weaker than spec, but according to the shop not enough to account for the issues I have been chasing, and certainly not a reason to send it to Garmin for refurbishment.  So now the troubleshooting focus will be on the blade antennas and the two coax cables coming together at the power combiner that is located at the tail.

[Baker Avionics]

If you swapped the antenna coaxes behind the panel at the racks, that all but eliminates the splitter.  The antenna is in good enough shape because of the 155 working fine.  Things to check are to see if one of the grounds on the Nav connector has come loose or is not making contact. Also, be sure the screws on the backplate are tightened because a loose connector can not fully seat correctly causing intermittent issues.  

[FLYFST]

6 hours ago, Baker Avionics said:

If you swapped the antenna coaxes behind the panel at the racks, that all but eliminates the splitter.  The antenna is in good enough shape because of the 155 working fine.  Things to check are to see if one of the grounds on the Nav connector has come loose or is not making contact. Also, be sure the screws on the backplate are tightened because a loose connector can not fully seat correctly causing intermittent issues.  

Thanks, I will.  Right now I'm in the process of removing the blade antennas, checking for any corrosion, and cleaning that up as necessary.

[FLYFST]

Troubleshooting update #2, I have to replace at least one of the blade antennas.  The following is a bit detailed but I am providing in the hopes it will benefit someone else, as the advice and suggestions from this forum have helped me.

All the cabling, connectors, and GNS-530 NAV-1 check out, but one of the antennas is apparently bad.  Measuring the resistance for each antenna at the BNC connector, between the center pin and outer shell, one antenna indicates a small (0.3 to 0.5 ohm) but definite resistance while the other indicates an open circuit.  I contacted Cobham Customer Support, and they were very responsive and helpful!  They explained that each of the CI-120-1 blade antennas should have a 'short' circuit resistance reading between the pin and outer shell, and that 0.3 ohms resistance indicated a good antenna while the one indicating an open circuit is faulty.  In my installation the two CI-120-1 antennas each connects to its own coax cable (CI-120-2) and both cables come together in a power combiner (CI-120-3), from which a single coax cable goes to the cockpit to a Dual VOR / GS Antenna Coupler (CI-505).  The CI-505 splits the signal and has two separate VOR/LOC outputs, one for each NAV radio, and a Glide Slope output.  According to Cobham, the CI-120G-S is a balanced system consisting of the antennas (CI-120-1), cables (CI-120-2), and power combiner (CI-120-3).  A malfunctioning or not working antenna (such as I appear to have) would throw the system out of balance and can result in the kind of issues I reported at the start of this post.

So now the next step is to find a single used antenna that is in good enough shape but with undetermined performance qualities to balance against the rest of my working system components, or spend ~$1,200 for two new blade antennas and reuse the cables and power combiner, or get a complete CI-120G-S for ~$1,500. 

[carusoam]

Are you familiar with the used avionics guy around here?

Do you have a pic of the antenna that you are looking for?

Nice pirep!

Best regards,

-a-

[FLYFST]

19 minutes ago, carusoam said:

Are you familiar with the used avionics guy around here?

Do you have a pic of the antenna that you are looking for?

Nice pirep!

Best regards,

-a-

I sent Alan Fox an inquiry and I am waiting for his reply. Also, look back near the start of this thread where I did post several pictures.  Thanks for the suggestion.

[carusoam]

Ohhhh... that one... yeah, I even remember That one.   

Said the guy with age related memory challenges...

Best regards,

-a-