Troubleshooting broken ILS/LOC on KX-175B + KI-214

Minimuffins

Minimuffins

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Minimuffins
Howdy folks,

My first time posting here. I have a 172E that I've had for about a year and it has some older avionics that I believe is not working to its full potential. The relevant pieces are a KX-175B and a KI-214 (066-3025-01).

The com works great. VORs work, but ILS/LOC does not seem to work at all.

Where should I start in troubleshooting this thing?
 
AV8R_87 said:
Pin 4 on the KX-175 is the ILS ENERGIZE discrete. Should connect to pins V and F on the KI-214, is what tells it to switch from VOR decoding to LOC decoding and activates the GS receiver that is built into the KI-214.
Page 2-19 from the KX-170B/175B install manual.
Available here: https://www.csobeech.com/files/BK-KX170B-KX175B-Install.pdf
Click to expand...
That's really great info, gives me something to try. Thank you.

Other than eyeballing the connectors and wiring to make sure the right pins appear to be connected to each other, can you think of anything I might be able to do to confirm that it SHOULD be working? Can I use a voltmeter to test something somewhere?

I actually have two KX-175Bs and I have tried both in the same slot and gotten the same results, so I don't suspect the radios themselves. They have also been bench tested at an avionics shop last year and confirmed to be good. I suppose the KI-214 could be bad.

I'm really not very knowledgeable about the setup here. Could it be an antenna issue? If VOR works, should I expect LOC to also work (assuming the 175 and 214 are wired together the right way)?
 
Use a cheap(ish) multimeter in either ohms or diode/continuity mode (better because it beeps if the wire is intact, you don't have to watch the screen). Chech wire continuity between the pins I mentioned, and also ring it to ground, to make sure there isn't a short-circuit somewhere.
With VORs working I wouldn't suspect the antenna or most of the other wiring to the KI-214, which sends the tuning information. The KI-214 itself could be bad, but it would have to be a dual LOC and GS failure, which is less likely than the one wire from the main radio whose function is to turn both of them on.
 
Ok, so I've learned some things.

The ILS Energize wires seem to be hooked up properly. There's continuity between Pin 4 on the KX-175B connector and Pins V and F on the KX-214 connector.

However, from this diagram it looks like Pin 19 (ILS Common) on the KX-175B is supposed to be connected to Power Ground (it is) and Pin C on the KX-214 connector (it is not).

KX-175-ILS-Common.jpg

From the diagram it looks like I should either run a wire from the KX-175B connector Pin 19 (which also goes to Power Ground) over to Pin C on the KX-214 connector, or maybe instead just connect Pin C to Pin U like this:

View attachment KI-214-connector-connections.jpg
 
Careful! Pin U is not a ground. It is an input for the actual VOR/LOC signal. What you're seeing is the ground going to the shield of that wire, and I wouldn't touch that.

Complete lack of a ground on Pin C of the KI-214 should prevent the operation in VOR mode as well. I wonder if your problem is a bad ground (you could be getting some grounding through the panel) and it only manifests itself when the higher power draw of the glideslope receiver comes into play. Adding a ground from pin C to pin 19 won't hurt, even if it doesn't fix your problem. Worth trying.
 
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