KNS 80 DME not working

[Dana Perez]

Hi guys! I hope you can help.  We have a KNS 80 in our Bonanza and we noticed recently that the DME is no longer working. However the VOR signal is and we can track the VOR no problem.  We're just are not receiving DME/Speed/.  I was hoping to just replace the KNS 80 with a used one, but is that sure to solve my issue? Or is there another box or item that could cause this issue. I thought maybe the Antenna, but then we wouldn't be receiving the VOR either, right?  Any words of advice? Anyone have a KNS 80 in good condition to sell? Any help from your guys is appreciated.

[Donald Lawrenz]

The KNS 80 contains an internal DME section. That is what has failed in all likelihood with your radio. If you purchase a used one as a replacement it may very well work,     or not. Repairs are usually not expensive and then you know you have a viable unit. Ask your avionics shop about their capability. If they cannot competently repair the radio there are several shops that you can send the radio to who perform that service. One is Bevan-Rabel in Wichita.

[Robert Siegfried]

Hi Dana-

I agree entirely with Don's advice, but let me make one additional point since you mentioned the antenna. The VOR section and the DME section of the KNS-80 use different antennas, so a bad antenna or connection cannot be ruled out based on the fact that the VOR section is working. Having said that, I think it more likely that the problem is with the KNS-80 and a bench check by a good shop would be my first step.

Regards,

Bob Siegfried, II

[Dana Perez]

Thanks Robert and Don.. I started a conversation with an Avionics guy, and he too said there are TWO antennas so we are not ruling out an antenna or cable issue.. but he also agrees it is most likely the BOX.. So we are going to bench test it or swap it to test the antenna and cables.. then move on.. but I will not overhaul this unit.. I think we got a quote for that and it was well over $1800.. and we have a cracked and crazed lens as well. So if I can find a good used one,I think I am better off.  Thanks for your advice, I will follow up and let you guys know what we find out.

[Dana Perez]

Update! So here is what happened to us...

So we ending up buying a Bench Tested KNS 80 replacement. I felt like this was the answer.  We took out the old one, and put in the new one.. it was hard to get back in... but it did go in. And it didn't go all the way flush... but it was tight and secure.  I went flying.... I was getting a DME reading that was CORRECT, but not calculations of KT or MINs.  And our VOR Indicator had a flag.  So I landed and the next day I tried again. I reseated the KNS 80 again, it was in all the way it would go.  The next test flight, better, but still not right. Now we had no Flag indication, and the VOR was receiving.  We had a good DME but again no KT or Mins.. and the VOR indicator did not show a TO /FROM indication at all.  The needles just swung back and forth.  We were disappointed!  We had an Avionics Mech.. look at it too. The only thing he could figure is that the unit was not going all the way in... but why?  We are not sure.  Bottom line, we have to send back the KNS 80 to the seller. :-(  When we put back our old unit.. OH it fit so nicely in and I could FEEL it engage.  We got our VOR indication back and all was back the way we started.  We have VOR tracking but no DME indicators.....

If you think you know why this happened let me know.  Also if you ever have a KNS-80 you know works and you are willing to let us try it, please let us know.  For now we decided to keep our old one and use the Reliable VOR only signal (as a back up of course)  We do have a Cert. Garmin 430 for primarily nav.

Thanks for reading and listening!
Dana

[Donald Lawrenz]

Were any tags taped on to the unit? Those often cause a problem. The other problem is if the locking tang is not properly positioned and fully seated by turning the adjusting screw completely in. The box may well have been prevented from fully sliding end by the very tab that locks it in place. It does take some effort to turn the screw mechanism that pulls the box home.

[Dana Perez]

Donald,

Thanks for your response. We made sure it was in as far as it would possibly go.. it was TIGHT.  We also had an avionics guy do it as well.  I believe you are right.. it was not "sitted" properly.. but I think it was a problem with how the newer one fit vs the older one.  Do you know if the connections, or CARD at the back are different from different models. Our model number was in the 5000s and this one was in the 11,000s.   What bothers me is that the two unit did different things when in.... anyway, we decided to just let it go.  No point CHASING the problem since that is just a back up for us.  At least the old one gives us ACCURATE VOR signals and tracking information.  The newer one didn't even give us that.

[Donald Lawrenz]

I don't believe there is a difference in the connectors at the rear of the unit for the same model. Your avionics guy should have/probably did check that. You would have to compare model numbers on the data plate to be absolutely sure.

It is also possible that there is a problem with the connector mounting in the rack. that could cause both an alignment/seating problem as well as a non-functioning portion of the box. Not highly probable, but it does occur.

Don