MX 170B not receiving comm

AU_James

Pre-takeoff checklist
Joined
Feb 7, 2017
Messages
213
Location
FL
Display Name

Display name:
James
BLUF: the comm side of my nav/comm doesn't seem to work and I'm debating whether to spend money for somebody to chase it down or to buy a replacement unit.

A little over a year ago my second nav/comm (MX170B) started giving me issues on the comm. Being VFR only, I just used it to pick up weather at my destination while staying on flight following. Losing that capability is an annoyance, but no big deal. Now that I'm into my IFR training, I need to get it fixed.

First, the Nav side works fine. I'm able to tune into and identify VORs without issue and the HSI works. It will mirror what my 430 is doing. I haven't tried it on a localizer yet but I would imagine it works fine considering.

On Comm, when the unit is powered on I can hear some faint background hiss even when Comm2 is not selected for me to listen to on my audio panel. The hiss goes away as soon as I power off the MX170B. While on, there is a "tic" in the comm window that should indicate transmitter power. I've also tried the "test" button which should override squelch and still hear nothing.

When this first happened, I asked a mechanic to look at it while doing something else. Didn't find anything. During the last annual, non-avionics specialty folks spent a little bit of time just to make sure all connections were secure and to look for anything obvious. Nothing found.

It's frustrating because it seems like it could be something so simple and just "messing around" with the connections or ensuring no interference is occurring would fix it. I even cleaned the antenna on the bottom of the plane to make sure grease wasn't blocking signals. But, I need this thing to work now and I'm hoping somebody else may have some advice or experience with this sort of thing.

If I replace it, also looking for thoughts on whether it's a good idea to go used/ebay or to buy something online. I also assume I'm looking at a KX155 or MX170C but is there something else out there that's a slide-out/in replacement?
 
Sounds like something in the radio has gone bad, but for a simple test do you have any friends with a plane and similar radio so you could rack yours in to theirs ? If problem follows radio it’s the radio. You could probably also get yours tested/repaired by TKM for cheaper than buying a replacement. KX155 would be a total rewire and if doing that I would just buy a brand new com with warranty (trig, Garmin, etc).
 
Thanks for the input. Does TKM test/repair an old Narco system, assuming it's really the same box?

I don’t understand the question... If you have a MX170B it was made by Michel’s/TKM out of Scottsdale. Not sure what Narco has to do with it?
 
If you have a MX170B it was made by Michel’s/TKM out of Scottsdale.

Ah, ok. I thought it was a Narco product. The antenna says Narco, the equipment was listed as Narco when I bought the plane, and when I looked it up long ago the image popped up with Narco associated. Obviously I did a tremendous job at due diligence.... :oops:

Doing more digging, I guess it's not Narco at all. That's actually a relief.

Thanks for the help.
 
The MX170 is a slide in replacement for a KING KX170.
The King radios were the industry standard but were new in the 70’s-‘90’s.

The older MX series aren’t supported by Michaels anymore. Newer ones, such as the MX170C’s are. Warranty repairs are $99 plus parts and shipping for the last one I had repaired. Obviously the reason most avionics techs hate them!!!
MX12’s were slide-in replacements for the Narco Mark 12 series radios.

Log books should show the replacement, even though a pilot/owner can do the swap. Most don’t, though...

If you were still close to Auburn, you could come to my airport and I would let you try some of my old -accumulated KX170’s on the shelf to see if one would work. Most were replaced when it was cost effective to replace with the Michaels unit when they were $1,250. Now they’re 2x more and you are better off with new Garmin, or such equipment. Ask around, someone may have a “loaner” you can try out. My bet is that the reciever has problems. At $400+ a pop to have repaired, it soon becomes cost prohibitive to fix them...

Contact Michaels in Arizona to see if your unit is still supported. You’ll need to provide the serial #.
 
Last edited:
Thanks for this reply. I was going to pull the unit this weekend and at least record the serial number and try to clean connections and the like. I assumed it would not be supported anymore, and the entire debate is whether to "try" to get it fixed and run the risk of not being any better off (but being lighter in the wallet) or just buying something that's currently supported.

There's also the ever-present question about whether it's just time for an upgrade. Lots to consider, but I appreciate the info!
 
Back
Top