(Old) transponder repair

[Hugh_Jarse]

Next year most of my avionics are going to be replaced, but my transponder has decided it can't wait, and has started playing silly b*ggers. Mode A is corrupt, and Mode C had me somewhere near orbit yesterday, according to ATC !

It's an old Cessna 400 unit. Does anyone know who might do a quick (reasonably priced) running repair, or where I might buy another second hand (again, reasonably priced) ? I really don't want to start upgrading the panel just yet.

For those who are into this stuff, this has coincided with the autopilot (Cessna 400 again) disengaging after about 30 seconds for no apparent reason ...)

Thanks for any help / advice.

Hugh

[BackPacker]

There should be lots of 2nd-hand Mode A/C transponders for sale in the Netherlands right now, with the mandatory upgrade to Mode S. You might even be blunt and start cold-calling some avionics shops in the Netherlands to see if they have anything lying around that is a drop-in replacement for your existing unit.

With regards to the autopilot disengaging: any chance they're using the same alticoder output?

[Big Pistons Forever]

With respect to the Transponder, Airwich in the USA has a huge inventory of used Cessna boat anchors.....er excuse me Cessna Avionics. The other option is a new slide in replacement unit like the NARCO AT155R. However one of the problems with Cessna radio packages is the poor quality factory installations. When my transponder stared acting up for the second time I replaced it with a Garmin GTX 320. I am extremely happy with it. There is no warm up it, draws about a quarter of the power, and is lighter.

With respect to the autopilot, it is vital that you provide a comprehensive list of what it is actually doing or not doing to a repair facility. For instance

1) Does it correctly self test on the ground? If yes wait 5t min with engines running and radio master on and repeat. Does it still self test ?

2) Start with aircraft in trimmed level flight with A/P off. Does the electric trim work smoothly and correctly ?

3) engage A/P with heading bug on current track with alt hold off. Does A/P follow heading bug? does the roll control knob work ?

4) engage alt hold. Does the aircraft immediately pitch up or down ? Does the pitch control wheel work ? Does it work smoothly and equally in both directions ?

5) If the A/P kicks off, how long before it stops working ? Can it be reengaged? Does all of it stop working or only part of its functions?

6) Does the nav tracking work ? will it intercept and track a nav course ?

Providing a clear description of the probem will save you big money at the Avionics shop.

[Hugh_Jarse]

Thanks for the steer, guys.

Anyone recommend a good avionics repair shop in the northern half of the UK ?

[KeesM]

I've a KT76A for 50 euro ex. postage. Replaced it with a mode-s earlier this year. It comes with a Trig tray. The Trig fits the KT76A tray, not sure if it works the other way around.

-Kees.

[IO540]

You could pick something up on US Ebay e.g. here (http://motors.shop.ebay.com/Aviation-Parts-/26435/i.html?_nkw=transponder&_catref=1&_dmpt=Motors_Car_Truck_Parts_Accessories&_fln=1&_trksid=p4506.c0.m282)

It probably won't come with any paperwork though. Make sure the seller will ship to the UK ;)

[gasax]

A recon Cessna transponder is over $1000. Might make more sense to either start the avionic upgrade now, or use Ebay etc to find somehting that works. Replacing a Cessna unit with a Narco is a bit like changing a broken shovel for one without a handle!

[First_Principal]

One of the biggest causes of failure with these things comes down to connectors - if you're a handy type with suitable sign-off you could slide the unit(s)out & clean what connectors you see with a rubber and/or suitable cleaning fluid, slide them back in & test. It could well sort things out so it'll last through 'till your upgrade.

If you're not able to do it yourself I'd certainly ask an engineer to try that for you before you contemplate much else.

FP.