KX-175B audio distortion

Pilawt

Pilawt

Final Approach
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Pilawt
I have a pair of KX-175Bs (28v) in my C-172N. They're listed on the National Register of Historic Avionics, but have served well.

Recently #1 receiver has occasionally been getting distorted in flight -- all transmissions, from ground, air, ATIS, etc. It gradually comes and goes. Today, for example, it was clear on takeoff, but by half an hour into the flight everything was loud but unreadable from distortion on all freqs. By the time I was in the pattern of the destination twenty minutes later, it was clear again.

This has been happening only on occasion and unpredictably; not yet consistent enough to take to a shop.

Ideas, suggestions welcome.

Thanks.
 
That radio is 2 generations into the registry. It is also one of the most robust and well designed radios ever built. There are very few people that will work on them any more. There is one guy that specializes in them. It may be worth it to have him take a look at it, maybe not. It might just be time to start looking at a new radio install. Stay away from last generation used stuff. Mark12s, kx155 etc they are orphaned for the most part. Sine a large part of the cost is instillation it really is best to go with a new design. The lower end is the Tkm which is a slide in replacement at about 3k.

Bob
 
Thanks, Bob. I saw the website of the guy who works on KX170Bs (http://www.kx170b.com/) -- if the problem is intermittent he doesn't want to look at it.

The TKM MX170C sounds like a good option for my purposes. They're just up the road here in Scottsdale. I need to be sure that unit works with 28v.
 
Are you using a lighter socket USB charger in the plane? I have a K175B and found it susceptible to noise from the charger when it was in use (I assume actively charging).

I've now had a panel USB installed and no issue since.
 
CMongoose said:
Are you using a lighter socket USB charger in the plane? I have a K175B and found it susceptible to noise from the charger when it was in use (I assume actively charging).

I've now had a panel USB installed and no issue since.
Click to expand...

Hadn't thought of that. Yes, I do have a USB charger in the lighter. I'll check it next time out. Thanks!
 
Might it be heat related? Our 172M had a forced air plenum that was clamped on either side of the radio stack and was connected to small airscoops outside.
 
CMongoose said:
Are you using a lighter socket USB charger in the plane? I have a K175B and found it susceptible to noise from the charger when it was in use (I assume actively charging).

I've now had a panel USB installed and no issue since.
Click to expand...

What kind of Panel USB did you install?
I have the issue where when I plug into the USB port it breaks the squelch on the radio even with the squelch turned all the way up.
I am partly suspicious that the USB cable(s) I have tried might be the source of the RF noise also.

Thank You

Brian
 
brcase said:
What kind of Panel USB did you install?
I have the issue where when I plug into the USB port it breaks the squelch on the radio even with the squelch turned all the way up.
I am partly suspicious that the USB cable(s) I have tried might be the source of the RF noise also.

Thank You

Brian
Click to expand...

I had the stratus installed. There wasn't much research behind it, I just happened to be installing the Stratus ESG and the shop had experience with their USB power supply too.

In hindsight the Mid Continent Clock and USB combined might have been a better option for panel space, but I've no complaints with what I have.
 
Update ... The distortion reoccurred today, but this time not bad enough to make transmissions unreadable. It only started at the end of a half-hour flight, and I noticed that it varied with engine rpm. Bad mag shielding maybe?

I had removed the USB charger, so ruled that out as a cause.
 
Well, one can get to the point where it doesn't make sense to throw good $$ after bad? You may not be to that point yet, just reminding.

A while back I messed with($$) a KX-175 for awhile. I eventually got an SL-30 installed & life was SWEET. It may depend on where you fly and how important comm is? It's a drag to have others complaining out your radio all the time.
 
The cigarette USB charger was a good idea. Since you eliminated that, be aware that a portable battery USB while charging an IPAD/IPHONE has also cased distortion in my KX170B when the components and/or wiring was too close to the panel. Make sure any of these portable charging devices are far enough away, or experiment in flight.
 
Just a guess, but since it starts a bit into a flight and comes and goes, I would bet on a temp problem on a component in the radio. Very hard to track down and fix.

Bob
 
unsafervguy said:
Just a guess, but since it starts a bit into a flight and comes and goes, I would bet on a temp problem on a component in the radio. Very hard to track down and fix.

Bob
Click to expand...

In the plane yes, on the bench no... if you can get it to repeat with a heat gun. Once it fails, then use some freeze spray to isolate the component
 
unsafervguy said:
Just a guess, but since it starts a bit into a flight and comes and goes, I would bet on a temp problem on a component in the radio. Very hard to track down and fix.
Click to expand...
I've kinda narrowed it down between this and a dirty antenna connection. (But how could that be? The radio has only been in there forty years!!) o_O
 
Pilawt said:
I've kinda narrowed it down between this and a dirty antenna connection. (But how could that be? The radio has only been in there forty years!!) o_O
Click to expand...
Where is the antenna located? Normally when I get that type of write up I remove antenna from airframe and clean the mating surfaces and put a new gasket and reseal because if there is a little bit of moisture between the antenna it will cause static. Also clean connectors on both sides.
 
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