KDefran

It appears as though my glideslope woes have been fixed. I sent the KX155 to Bevan Aviation. They were great and talked me through my options and were able to get it fixed for a reasonable price. Today, I flew the plane and both of the glideslopes worked as expected! In the end, it appears as though there was not a common cause and both units independently had failed glideslope receivers. Thank you everybody for the help and guidance!

I just wanted to follow up on this topic. I recently got the airplane back from its annual inspection. While it was there, I made the decision to send the GNS530 to Garmin for refurbishment. This has appeared to fixed the problem. I've taken it on a few flights so far and have had no issue with the ILS glideslope at a couple of locations. Since this fixed the problem, I will likely send the KX-155 for refurbishment next time the plane is down for a while. After all was said and done, I was wrong that it was something to do with the splitter, but I'm glad it is working.

Problem is still not fixed. I tried to do some troubleshooting with a glideslope antenna inside the cockpit and the splitter removed from the equation. It appears to confirm that both the 530 and KX-155 are not processing the glideslope signal. Next annual I am planning on sending either the 530 or the 155 back to the manufacture to repair. If the manufacture fixes one, then the other one is probably fixable too. I still find it hard to believe that two relatively independent units failed in the same way, but that is what the evidence is saying.

https://www.aircraftspruce.com/catalog/avpages/ramiav585.php Here is the diplexer/splitter that I'm talking about. The coaxial from the antenna goes into the input, and there are 4 outputs; 2 VOR/LOC and 2 G/S. I'm not exactly sure what the term diplexer means, but I guess it acts more as a splitter.

UPDATE: Looked at the airplane today and found something weird. Coming out of the diplexer there are 4 coax cables, 2 VOR/LOC and 2 glideslopes. It appears as though the wires were switched. Basically the VOR/LOC output from the diplexer would go to the glideslope input for the unit. The opposite was also true with the glideslope output was routed to the VOR/LOC inputs. This was the case for both the 530 and 155. I switched the wires and noticed immediately that the localizer needle moved more forcefully however there was still nothing on either glideslope. I decided to take it up for a flight to see if the glideslope would work while on final approach. I took it out to about a 4 mile final and the localizer worked normally, but there was still nothing from either glideslope. However at about 2 miles the glideslope started working on the 530 only. Still nothing on the 155 though. The working glideslope on the 530 provided correct indications based on the PAPI lights and worked from about 2 miles all the way to touchdown. Questions that I have: -I think I understand the basics of the diplexer in that it will only send the correct frequency for the VOR/LOC and G/S respectively, but what is it's actual purpose. Apparently for the past 2+ years my VOR/LOC has been working just fine while receiving the G/S output from the diplexer. -Would the wires being backwards have any damaging effect to the units. Basically would 330hz signal going into the localizer be bad for the unit? I suspect not but I'm not sure. It seems like that there is some bleed through of the frequencies from the diplexer. -Fixing this specific issue still has not fixed the problem. My plan going forward is to still remove the antenna from the equation based on Jerry 5TJ's recommendation. I ordered an antenna which should arrive this Friday. If I connect the antenna directly to the G/S inputs there the results should help point in the right direction. Thanks everybody for the helpful advice so far and I look forward to finally fixing this.

-Engineer yes, great memory no. Learned about it years ago and it just stuck. I'm not as familiar with my antenna as I should be, but I'm going to become more familiar with it. I'm definitely a fan of WAAS approaches so that's why I'm not in a big rush to fix the ILS. I'll have to ask around to see if there are any 155s to check it with. I'm not sure of the process that he used. That will be a question for me to ask him as I never would have thought of that. This might the the cheapest/easiest way to test the units myself. I'm going to do some searching for a good internal antenna to buy/build and that should eliminate some variables. I don't remember the exact prices, but I think the 530 was quoted as about $1,200 and the 155 as about $1,600. Both prices were more than I was will to spend until I could determine that was the actual problem. Thanks everyone for the replies. As I continue to work on the issue I'll keep this thread updated with what I find.

Hello All, This is my first post, but I've been reading and learning a lot from this site for years. I have been having an issue with my ILS glideslope since I bought the plane ~2 years ago and still have not figured it out and I'm hopefully that some members might have some ideas that I haven't thought about yet. The NAV/COMs in my airplane consists of a GNS 530W and a King KX-155. When I bought the plane, the ILS glideslope would be very weak. Sometimes it would work, sometimes it would not. This would occur on both the 530 and the 155. I can't clearly remember exactly what was happening since this was approximately June 2016 In about August 2016, I took it to an avionics shop. They did some troubleshooting and replaced the coaxial splitter that has 1 input from the antenna and provides 4 outputs to the 530 and 155 with both a localizer and glideslope signal. This fixed the problem initially, and I don't know what other troubleshooting they did since replacing the splitter initially fixed the problem. After about a month, I could see that the glideslope was slowly starting to fail again. It failed gradually over the course of about another month or two where initially it worked, then it would only work in close proximity to the airport, and then it stopped working all together. Again this was for both the 530 and the 155, and they failed nearly simultaneously. Fast forward to September 2018, and I had a separate mechanic look at it since I had moved across the country from NC to CA. He shot all of the coax and said that a good signal was getting sent from the antenna to both the 530 and 155. His recommendation was that both the 530 and 155 had failed internally and that they should be sent out to get repaired. The minimum costs were quoted as about $1,500 for each instrument. I'm not a believer in coincidences; and 2 instruments failing in exactly the same way at exactly the same time is not likely. Occam's razor would suggest that there is something else that is causing this failure, but I do not know what it could be. Recently, I tried replacing the coaxial splitter to see if somehow that was the culprit again. However that did not fix the problem or change anything. The problem is isolated to just the ILS glideslope since the 530 works normally while shooting an LPV approach. Also, when I tune the frequency to the ILS, I can hear the Morse Code signal which makes sense since the VOR and localizer functions works normally. I'm running out of ideas what could be wrong. Now I'm thinking that there possibly could be something wrong with the antenna itself. Since the localizer and ILS frequencies are so different, maybe there is a chance that only part of the antenna is bad? I'm pretty sure the antenna is the original that is on the tail and has the "V" shape facing forward. During an annual, the sheet metal cover was off where the antenna is located and it looked like there was some tape holding the connections together. Since the localizer/VOR work I haven't thought too much about the antenna though. Maybe the A&P is right and both the 530 and 155 just happened to fail at the same time. But before I send the units off I just want to see if anyone has other troubleshooting ideas that make more sense. I feel like that was a lot of information, and I'm sure I forgot to mention something so please ask any questions that come to mind.