Kx170b issue

[Browncbr1]

hello all,

I seem to have a very weak KX170B or a not so good antenna.

Does anyone know how I could correctly identify if it is the antenna/connections, or the box? I seem to pick up VOR, but much later and higher altitude than my KX155 or KN64. I can't seem to get any Comm on the 170B.

I was going to put in a 430w, but given the high prices these days, I think I'm going to just going to get this #2 nav/com working again. At least for a little while. I've looked at McCoys, but figured that I would rather that money go towards something else. It seems I can get this thing overhauled for $200-300

Any suggestions on things to check before pulling the radio out for overhaul?

Cheers

Craig

[larryb]

VOR and comm are separate circuits and separate antennas. Sounds like more than one problem. I would suggest pulling it out and having it checked on the bench.

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[jetdriven]

Putting an SWR meter between the radio and the antenna can give clues. Also, if you can receive from 50-60 mm away but can only transmit 10 miles it could be an antenna. Mine was doing that, instead of measuring RF power the shop tuned it up for 200$, but the problem persisted. Turns out it was the 400$ antenna. Had I been smarter, I would have swapped antennas at the radio to see if the problem followed the radio or the antenna. The 170B is a good solid 1970s mechanical / transistor radio. Hope this helps. Then

[Browncbr1]

Thanks for the input Larry.

[ryoder]

I bought a MX170 for 1850 to replace my kx170. I might put the 170 back in if I sell the airplane and sell the MX170 for 1600 on fleebay.

Could be an option for you too. It slides in in five minutes.

[Browncbr1]

Hi jet, yea, that was my thought too... Switch antennas and see.... Is it a simple plug on the back of the racks that I can easily swap?? I'm thinking I better just pull it out so I can learn more about that stuff

[jetdriven]

Swap com 1 and com 2 in the rack. Don't do this For IFR flight becuase u can't be sure the glideslope works nor the vor accuracy. But, anyways, swap them In the cans and see which radio is weak after that. In a j model the coax for the antennas is near the pilots right knee under the panel. Two inline connectors to the com antennas. You can swap them there.

Nvm the radio swap in the rack u have a KX-155. Not the same rack.

[Browncbr1]

Thanks jet. I'll look for the comm coax and see if I can get them switched.

[N601RX]

Many planes are still flying around with 30-40 year old coax that is in pretty bad shape. Extra should be coiled up loosely, not exceeding the min bend radius. I had some I my plane where some well meaning mechanic had bent it back and fourth on itself and pulled it down tightly with cable ties. That destroys the impedance. If it looks bad replace it with RG400 which is low loss and double shielded. It will be a light tan color while the old RG58 is black. Also on an otherwise corrosion free plane you may find a white layer of powder between the antenna and skin if it's never been removed. This will keep the antenna from working correctly as it doesn't have a ground plane. Look at the ends, if the coax is not supported correctly they may look like the one in the picture that was causing problems. Notice the shield it completely broken.

You will also have a diplexer behind the panel that splits out the localizer and glideslope. There is also a bulkhead bnc fitting where the coax from the nav antenna passes from the tail into the empennage.

[Mooneymite]

This web site has some troubleshooting suggestions for the 170B:

http://www.kx170b.com/

[Browncbr1]

Thank you all for so much help.

Once this ice storm passes, I'll have a look at the wires, connections, and try to see if the comm antenna is well grounded.

[Mooneymite]

I am thinking about upgrading my KX170B to include a glideslope. I would need to purchase a KI209 & KN-75. Does anyone have a better idea.

 

Thanks,

Pat 

 

As you know, the GS receiver is not located in the KX170B, it is located inside the KI214 indicator.  The only function of the KX175 with respect to GS signal is to tune the KI214.  There is no actual "up-grading" with respect to the Nav-com itself.

 

Used KI214's are readily available, but they need tweeking every few years, so add in the cost of alignment when you buy one.

[HRM]

I have a KX170B and a KX155 and I think the 170 is the better radio. Anyway, before spending any money, and to summarize what has been posted, I would:

 

1) Pull, clean, replace the radio in it's bay. How far you go with this step is directly proportional to the size of your...

 

2) Check antenna coaxes, swap, clean connectors, test. If the coax is original consider replacing. Very easy to do if you have Bruce Yaeger's Spatial Interior (yeah, shameless plug).

[Dan M20E '66]

I had the same problem with my 170B - NAV worked great but COM range was feet, not miles. LASAR found it to be an antenna issue - don't know the details. COM works great now...

[Browncbr1]

Update, my entire unit turned out to be toast.

Antennas, wiring, connections seem ok. Slid another radio in and it is ok.