Can anybody identify this box?

[peter-h]

It lives under my RHS front seat.

There are two connectors, both at one end. One is like a DB37 though I have not counted the pins. The other is a BNC with RG400 cable going into it.

http://www.zen74158.zen.co.uk/temp-files-ph/converter.jpg

I ask because following an avionics test, it was discovered that NAV1 VOR information shows incorrectly on the HSI, but shows correctly on the KI-229 RMI which is switchable NAV1/NAV2. Also, NAV1 LOC/GS displays fine on the HSI. So the problem cannot be the NAV1 radio (a KX155A) itself; it must be something driving just the B/King HSI.

This problem has existed for a long time in that I occassionally saw strange behaviour on NAV1 VOR but remained unchecked because I use the HSI with GPS only.

The avionics man thinks the box is a KN72 converter and is the cause of the problem, but looking at images on the internet a KN72 has different connections on it.

I have the 2006 ATP CD for the TB20 aircraft but unfortunately do not have any details of what is actually installed in my aircraft.

The box might also be something to do with a KI-229 RMI which I had installed as a factory option...

The HSI fault shows up as:

As the injected signal is reduced (via a direct cable connection) at about -90db the HSI deviation bar and the to/from flag goes walkabout, but the Invalid flag doesn't come into view until -115db.

Obviously, the Invalid flag should be visible before the deviation bar or the to/from flags start to show rubbish.

NAV2 is fine, dropping the flag into view at -115db also.

This goes to prove that a VOR receiver cannot be trusted as the anti-GPS lobby here in Europe would make one believe

 

[wabower]

One of my airplanes had an inverter mounted under the seat to power one of the retrofit displays. Don't remember the details.

It lives under my RHS front seat.

There are two connectors, both at one end. One is like a DB37 though I have not counted the pins. The other is a BNC with RG400 cable going into it.

http://www.zen74158.zen.co.uk/temp-files-ph/converter.jpg

I ask because following an avionics test, it was discovered that NAV1 VOR information shows incorrectly on the HSI, but shows correctly on the KI-229 RMI which is switchable NAV1/NAV2. Also, NAV1 LOC/GS displays fine on the HSI. So the problem cannot be the NAV1 radio (a KX155A) itself; it must be something driving just the B/King HSI.

This problem has existed for a long time in that I occassionally saw strange behaviour on NAV1 VOR but remained unchecked because I use the HSI with GPS only.

The avionics man thinks the box is a KN72 converter and is the cause of the problem, but looking at images on the internet a KN72 has different connections on it.

I have the 2006 ATP CD for the TB20 aircraft but unfortunately do not have any details of what is actually installed in my aircraft.

The box might also be something to do with a KI-229 RMI which I had installed as a factory option...

The HSI fault shows up as:

As the injected signal is reduced (via a direct cable connection) at about -90db the HSI deviation bar and the to/from flag goes walkabout, but the Invalid flag doesn't come into view until -115db.

Obviously, the Invalid flag should be visible before the deviation bar or the to/from flags start to show rubbish.

NAV2 is fine, dropping the flag into view at -115db also.

This goes to prove that a VOR receiver cannot be trusted as the anti-GPS lobby here in Europe would make one believe

 

[gismo]

One of my airplanes had an inverter mounted under the seat to power one of the retrofit displays. Don't remember the details.

Given that one of the connections is coax not to mention the lack of any heatsink fins, I'd say there's no way this is an inverter. My first guess would be a GS receiver but that's normally internal to a KX-155A. AFaIK, you do need an external nav converter for a HSI connected to a KX155A so there has to be one somewhere and it's likely the source of your problem.

Here's a KN-75 GS receiver.

http://www.seaerospace.com/king/kn75.htm

 

[peter-h]

The KN-75 pic matches - well done

Interestingly, the lower (NAV2) radio is a KX165A which plug-in replaced a KX155A, but the upper KX155A could not be thus replaced (NAV would not work). This probably fits with the upper (NAV1) radio having a converter after it.

 

[Doggtyred]

showing a pic of the coupling side of the device would be more helpful but as you are concluding, it looks a lot like an old KN 75 glideslope receiver.

 

[peter-h]

Yes, it is a KN75.

The KN72 was found under the other seat