Hello everyone, My 1966 182 has a STEC 50, model ST-178, which was installed in the mid 90's. Recently it started popping the circuit breaker when being used. At first it would only pop once in a while and it has progressively worsened to the point that it pops after a few seconds after being turned on. I would like to avoid the painful visit to the local avionics shop and make an attempt to solve the problem on my own but don't know where to start. Anybody have experience with this and willing to give some pointers on where to start? I've located the major components of the system but want to get educated before doing something stupid. Thanks.

Have you tried a new breaker? Same amps.

Yes, I installed a new breaker already and it didn't help. Sorry I should have mentioned that. Thanks.

If you can, trace the wires to and from. If any are not secured and/or may have rubbed through the insulation over the years it could short the system when the bare wires touch the frame. I'm not an avionics guy and I did not stay in a Holliday Inn last night. Good luck tracking it down

CW

For really good reason, the FAA now recommends that when a circuit breaker pops, it shouldn't be reset. I believe that the impetus for this recommendation is an accident involving a 310, which had an inflight fire due to a short circuit in the (I believe) the radar circuitry. The pilot who had the initial problem didn't try to reset it, but no one placarded the switch or the CB, and a subsequent pilot reset the breaker. Very soon thereafter a fire erupted under the panel.

So it's not something to play games with. If it were me, I'd be looking for worn insulation causing a short, using a multi meter, but I sure wouldn't reset that new breaker. The only reason they pop is due to an overload due to overheated wires--and a quick overload occurs when there's a short. If you can't find it yourself, your friendly IA will be the next step.

Cary

The interface manual is located here:

http://www.csobeech.com/files/S-TecServiceManual.pdf

If you are patient but not a sparky type, you can troubleshoot some of the problems without breaking things open.

You may be able to track down whether the current draw is to the base unit or one of the servo systems within a short amount of time. It will save some $$ to find out to be able to let your avionics guy know. The schematics are very complete in the link above. You'll need to take a trip to Radio Shack for some pins and sockets to bridge the interface to use your ammeter with.

Best of luck.

66skylane wrote: I've located the major components of the system but want to get educated before doing something stupid. Thanks.

After spending over two years of my life weight off of wheels, you've already done something stupid.
I've had pressurization problems, hydraulic problems, engine failures 100LL/Jet-A, Glass Cockpits go dark, you name it. The most scary was a cabin fire at FL390 over Detroit (could you imagine having to land in Detroit?)
Open flames in the Cabin!
Fortunately we were able to de-power the problem and extinguish the fire. It was a circuit breaker that allowed us to de-power the system. It was Old School Cabin lighting. It resulted in an AD that effected a large group/type of planes.
Do some sort of internet search and you will find out fire is not your best friend in aviation!
Before you take off the next time, ask yourself if you can actually fly the plane, and handle the emergency if everything quits. Will you have the courage to declare an emergency, then follow instructions provided?
If not, just keep pushing that breaker in…. maybe the problem will fix itself

237

BTW, sorry for being so tough, but this is a learning moment…..
The upside, you asked!

Skytruck,
Thanks for the comments. I've worn my finger down to a bloody stump pushing the circuit breaker back in and agree its time for a new approach

Trust me, the last thing you want in flight is a fire!
You can hold that breaker in as long as you want on the ground and the problem will eventually rear itself.
No such thing as an "In Flight Emergency" if you're on the ground
Keep us posted.

237

A couple of months ago I departed a friend's place in my 185. Climbed to about 8,500 feet, leveled off, and then the unmistakable smell of burning electrics greeted my nose. Prepared to turn off the master, I glanced at the circuit breakers and looked around the cabin for smoke. In short order the smell dissipated. I continued on to my airport and once on the ground took a closer look at the breakers. The one for the transponder was popped. I pushed it in, turned on the master, then the transponder and in a couple of seconds the breaker popped again. I pulled the transponder, pushed the breaker back in, and switched on the master again. Breaker held so I tossed the transponder in the nearest trash can (it had been repaired once already) and installed a new one.

Never push a breaker back in during flight, not ever. And absolutely never hold the breaker in while its trying to trip, not in the air and not on the ground, thats an invitation to a fire you can't stop. And here's why: Most of us are flying aircraft that were built before yesterday, and that almost guarantees that some hack has wired stuff incorrectly as things have been added and removed from the aircraft. When I refurbished the 185 not one circuit breaker actually was protecting the circuit it was labeled for, and that means that amperage it was protecting was incorrect. On top of that, the 185 didn't come with a lot of circuit breakers to begin with so each circuit breaker incorrectly protected lots of things, again with incorrect amperage. And if that wasn't enough, aircraft wiring is sized to pass a certain amount of amps, and almost certainly its size was now incorrect to whatever its connected to. The breaker is your last line of defense before the wiring starts to melt and the fire begins. If your airplane is wired correctly the breaker will do it's job, but if it's not, repeatedly pushing the breaker in, or worse yet holding it in is just asking for a fire.

My airplane is now wired correctly, and everything electrical has its own dedicated circuit breaker, of the proper amperage, and the wiring is the proper amperage. Bigrenna went through the same thing when he refurbed his plane. Others here have as well I'm sure. We can now trust our electrical system and its protection. Most everyone else, probably not.

In the rare instance when an electrical short exists that can't be located by removing equipment, or checking the obvious potential problem areas, you can locate it with a handheld magnetic compass and an automatic resetting circuit breaker (of the correct amperage for the circuit). Remove the wires connected to the circuit breaker in the panel, attach them to the auto-resetting breaker. Power up and the breaker will pop, reset, pop, reset, pop, reset, etc. Move the compass around throughout the aircraft near the wiring. Away from the location of the short the compass needle will show a big deflection every time the breaker pops. As you get near the short the deflections will decrease.

Oh, my wife has had two cars that had electrical fires (both Toyotas). In both cases all the fire department could do was contain the blaze until the wiring burned itself completely through. And that was long after the car's interiors were completely destroyed by the fires.

You can still safely find which part of the ap system is the offending unit yourself. You probably won't be doing anything your avionics mechanic won't be doing to locate it if you are using common sense. It isn't quantum mechanics, and you might find it fun to learn how your ap really works. I know I did.

I appreciate all the responses to my question. It's only about 20 degrees in my hanger right now so I'll wait for a wintery weekend day and fire up the heat in the hanger and do some troubleshooting. I'll report back on what I find. I'd love to hear more ideas if anybody has them.

Breaker was a good try to start as they can be pretty dang old. But i would work it like so...
You say it pops right away when you turn it on? Or do you turn it on then engage the AP then it pops?
The servos are pretty easy to eliminate because you can use just ALT mode(elevator servo), and HDG (aileron servo). If it only pops when you engage HDG and not ALT mode then you are getting pretty close.
Did that fix it? No?...
Disconnect the turn and bank and try again... did that do it? no?
Disconnect everything but the mode controller and try again... still ur breaker pops?
Examine power wire for a short if no short found then ur controller needs to be sent in for repair.

Good luck!

^^^^^^^^That.

Ive got a three position toggle switch on the panel to turn the auto pilot off/on/test. The breaker pops when going from off to on or off to test. It takes a couple seconds after turning to on or test and then it pops. This is prior to engaging ap. Ill see what I can find. Thanks PAMR MX for the help.
Chadd