Transponder intermittently squawking erroneous code

Fearless Tower

Fearless Tower

Touchdown! Greaser!
Joined
Jan 1, 2010
Messages
16,473
Location
Norfolk, VA
Display Name
Display name:
Fearless Tower
Had this happen on a couple legs of my recent coast to coast trip in the Baron.

I have a Collins TDR-950. Did 4 legs westbound to San Diego and 5 coming back to Virginia. On one leg (FTW-ELP) after taking off, Approach tells me to reset xpdr because apparently I was squawking a different code than assigned or selected on the unit. For most of that leg, the xpdr the 2nd and 3rd digits of the xpdr kept switching back and forth on what number they were actually transmitting. Eventually it settled out and Center issued a new squawk to coincide with what my box was actually transmitting.

The next few flights had no issues, but then out of the blue on my third leg yesterday (Springfield, MO to Huntsville, WV) the problem shows up again (this time only affecting the third digit). The final leg home last night, the xpdr again was back to normal.

Anyone experienced this kind of intermittent issue? I am wondering if it is something as simple as dirty connections in the box, or if it is something that will be more cost effective to buy a new xpdr. At some point, I will need to go Mode S/ADS-B. Wonder if that time is now?
 
I hear your pain. My rule is never spend good money on ancient pulse technology.

Virtually always, it is better to bite the bullet and go new.

Saying that, there will always be responses like " I wiggled the wire to the antenna." Or, I sprayed some Collinite 845 on it and it's perfect."
 
Humidity + light corrosion in the box? :dunno: Pretty funky sounding deal with the numbers transposing.
 
I'd speculate that it is just dirty or bad switches for the digits in question. It probably stems from not being used enough to keep the contacts clean.

Regarding how to resolve the issue, my course of action would depend on what my intentions were with the airplane. If the plane is a keeper and will be around for a while I'd look into equipping it with a modern transponder. Otherwise, if you're not planning on keeping the plane or just don't want to spend the money for a new transponder and installation I'd just look for a known good direct replacement for what is currently in the panel. eBay or the aircraft salvage companies are where I would start there.
 
Might just need cleaning, often funky problems in old electronics are caused by stray currents in scum, especially with high humidity.
 
Mine did that once. It was a KT-76C. A few months later I had the routine transponder check completed. No issues.

Few months after that (last week), I flew into Class D within a 30nm Veil and they informed me the transponder wasnt working. Scheduled an appointment at an avionics shop there on the field, got permission to leave.

Next day I flew around 10 minutes prior to entering the veil and had the tower at the Class D keep an eye on me. After about 10 minutes in the air it kicked on.

Day after that it never kicked on. I had to fly in for my appointment, got permission from ATC to enter the veil for transponder work.

Avionics guy said it was dead as a doornail, nothing coming out of it. They sent it off for repair.

My point in that is that it may by symptomatic of impending failure. I would have bought something used (new to me) that was solid state, but before I did that I set a $$ threshold. The repair was quoted to me at a broad range and even the high end of the range was less than my "buy a new one" threshold. It was $750 btw.

I'm flying around with a loaner transponder now. Next time there's a failure I'm getting something solid state and less prone to failure maybe something meeting requirements for ADS-B later.
 
At this point if I had to replace a TXP and had no other ADS-B equipment yet, I think getting the 330ES may be the most efficient way to go, because that covers all the requirements everywhere, and then you can use low cost equipment to get the ADS-B In goodies from the UAT side, and it'll play with a 750 in the future if you upgrade.
 
Thanks! I'll keep note of that. The problem with owning and airplane is that you suddenly want to spend money on it. Kinda like a house. I'm always doing something something to maintain my house, but I enjoy it.

My mechanic gets a bit annoyed at me, although I'm quickly becoming a frequent customer.
 
gitmo234 said:
Thanks! I'll keep note of that. The problem with owning and airplane is that you suddenly want to spend money on it. Kinda like a house. I'm always doing something something to maintain my house, but I enjoy it.

My mechanic gets a bit annoyed at me, although I'm quickly becoming a frequent customer.
Click to expand...

Yeah, because upgrades to airplanes can have what I call "ass benefit". The money I spent benefits my ass every time I use the plane; in safety, capability, comfort, and enjoyment. I'm not into airplanes to make money, I'm into airplanes to create good experience. Your aircraft dollar cannot serve both purposes, they are incongruous.
 
Henning said:
Humidity + light corrosion in the box? :dunno: Pretty funky sounding deal with the numbers transposing.
Click to expand...

That is kind of what I was thinking, but wondering how hard ($$$) it is to fix. I have another trip out to CA in two weeks and then it will be annual time. Wondering if it is worth having the avionics shoppes with it now.
 
Fearless Tower said:
That is kind of what I was thinking, but wondering how hard ($$$) it is to fix. I have another trip out to CA in two weeks and then it will be annual time. Wondering if it is worth having the avionics shoppes with it now.
Click to expand...

It depends on the location of the hardware. I'm not familiar with that model, so generically I would start with opening the control head and using a contact cleaner there first. Cleaning equipment isn't expensive or difficult unless you have a bunch of hard to reach remote boxes as well that need service.
 
take the face off, if it is the type that has the little copper discs on the back of the number selection knobs, you can carefully clean them with a pencil eraser, that often solves your exact problem
 
JHW said:
take the face off, if it is the type that has the little copper discs on the back of the number selection knobs, you can carefully clean them with a pencil eraser, that often solves your exact problem
Click to expand...

x2

haven't done this cleaning procedure myself but have flown with a lot of these old collins transponders and this is supposed to be the fix. I have seen "cleaned contacts" mentioned before in the squawk book of our club aircraft when someone complains about a fickle transponder
 
You must log in or register to reply here.
Back
Top