TruTrak autopilot query

[Gorilla]

Hi,

My name is Paul and I'm a CTSW owner and new to the forum.  I know that there are some great technical minds on this forum and I'm hoping someone can help me out.

I have recently installed a Bendix King xCruze100 (re-branded TruTrak Vizion) autopilot in my aircraft.  Everything works fine except for the GPS input.  I am using an AVMAP EKP V navigator connected to an external GPS antenna for the GPS signal to the AP.

The AP wiring diagram shows just ONE wire on pin 17 of the 25-pin multiplug which is for a NMEA 0183 protocol GPS input signal.  However, the AVMAP EKP V shows that I need TWO wires to connect to an AP; one connected to TXA and one connected to signal ground.

I have tried just using one wire to connect AVMAP TXA to the AP pin 17 but that didn't work; I had "NO GPS" displayed on the AP.  I have checked that the wire from the AP is on the correct pin and for continuity.  The BAUD rates are the same (I tried both 4600 & 9600) and the AVMAP works perfectly.

Has anyone on this forum got the same set-up as me and if so, how did you get it to work?  Can anyone shed any light on why the AP says it only needs one wire but AVMAP says I need two?

Thank you.

Paul

[Ian Melville]

You will need one data wire and one of the following:
Each unit must be wired to the aircraft ground
or
There must also be a second wire between each units ground.

It is usual to avoid earth loops (applying both the above). I suspect one unit will be grounded (AVMAP) and the other (BK Cruze) will get its ground from the grounded unit, hence two wires. If each unit is earthed, take the earth wire all the way to the common earth busbar, and not lash it under the nearest bolt on the airframe (IIRC the CTSW is GRP so you wont be able to use the airframe as a return wire anyway)

Some installation guides omit earth and power feeds to make the diagram clearer, but there is usually a comment somewhere. Without the full set of wiring diagrams ans manuals it is difficult to advise further.

[Gorilla]

Hello Ian,

Thanks for your reply. I did want to post some attachments showing both the AVMAP and BK xCruze100 wiring diagrams but couldn’t make the pages less than the ousting limit of 512K. Can I send you them in a PM?

Paul

[Ian Melville]

Yes you may

[AlanB]

I did have an EKP V driving a trutrack and had no problems.

Both units were connected to the same earth bus for power and so was the GND pin on TXa. As you say there is only one wire to the trutrak.

Another thing to check is that you have the correct messages out from the EKP V which you can select in the settings menu alongside the baud rate.

Another trick is to put in a route in the EKP V and activate it as from memory there were no messages if no active route in one version of the software. A GOTO would be an active route.

Hope that helps.

[Gorilla]

Hi Alan,

Thanks for that.  I'll give your suggestions a try. 

I know I selected the correct GPS messages and baud rates between the two devices and I did have a route activated in the AVMAP but I was trying everything whilst stationary on the ground - even though I could see that the AVMAP had "found" where it was.  I think I'll do the connections as suggested and then try everything out in the air.

Paul