S-Tec Altitude hold

[Topper]

I have an inop S-tec altitude hold. I am going in for a 650 next month and was going to have it fixed. I was in the tail area looking at the battery and noticed a couple of fuse holders, I was excited when i found one blown and thought maybe that was the s-tec problem. Long story short, the fuse had nothing to do with it. However, while I was back there I unplugged the S-tec computer and looked at the pins on the connector they were clean and did not show corrosion. The female side of the plug has some discoloration on it that might looks like corrosion, but was on the surface of the plastic insert that holds the female pins. I plugged it back in.

I replaced fuse and tested the S-tec and it seems to work. Felt pretty smart, but concerned about what blew the fuse. Turns out the fuse was not for it, so I think the problem must have been in the computer connection. I will have the avionics shop look at it, but if it is working I don't know that they can do much. Thinking about spraying the connector with some electrical contact cleaner.

Just wanted to get the thoughts of the more experienced.

Thanks,

Jim

 

[John Collins]

Jim,

If you want help, you will have to provide more information. What model of autopilot do you have installed? Describe what works and what doesn't work.

Here is an analogy of what I am talking about. What you have posted so far is equivalent to saying my ford doesn't work. It would be nice to know the model and year of the ford and what doesn't work. For example, the car has a blown tire, it is the RH front tire, and the tire size is ...

 

[Clark1961]

Bad connectors are the bane of some autopilots, that is for sure. If the darn thing is working then maybe tell the avionics tech what you did and get their opinion of the connector. Either clean or replace as they recommend. Corrosion can be a continuing problem and eventually it requires replacement of the connector if the corrosion is not stopped.

The Century autopilot in the Frankendota has it's own problems with connectors. Not corrosion but in design duty cycles. I don't disassemble without darn good reason.

 

[Topper]

It is an S-tec 30 Altitude hold. I also have the Cessna 300. It would light up, but would never engage and I don't remember hearing the servo in the past. Now it works (I think, I have not taken up in the air yet). The only thing I have done is unplug and re plug the computer in. I am guessing that it was a connection problem. My specific question is should I spray some electrical contact cleaner on the female plug?

Jim

FYI this is in a 1979 182

 

[airdale]

... I think the problem must have been in the computer connection.

The vast majority of electronic failures (and virtually all intermittents) are due to connection problems. I used to be in the spacecraft business and, there, when you asked the reliability guys for some numbers all they wanted to know was the number of connections in the bird. Jillions! is the answer. A wire-bond chip connection has two ends. A solder-bump is one connection. The package pads soldered to a board, the intra-layer board connections, board to chassis, etc. It goes on forever.

But the take-way is that the first step in trouble shooting is to unplug and replug connectors, cleaning them as close to perfection as possible. Card edge finger connectors are another usual suspect. A rubber pencil eraser with a little grit in it is a good method to clean and polish these.

 

[Topper]

Flew it this morning. The altitude hold works as it should. Not 100% positive that the plug was completely plugged in when I checked it. I think it came out without pushing the release, but can't remember. I will have the avionics shop give it a quick look and see if they see anything wrong. Can't wait to fly a cross country with it! Thanks for the input.

Jim

 

[weilke]

I will have the avionics shop give it a quick look and see if they see anything wrong.

Dont do it ! Dont allow them to touch it.

You said this:

Flew it this morning. The altitude hold works as it should.

At this point, there is no improvement possible beyond the thing holding your altitude if you depress that engage switch.

No upside, all downside.

Many tales of woe started with a tech 'giving it a quick look'. Pins get bent, litttle springs get unsprung, retaining screws get lost etc. That is not an attack on the particular tech or avionics techs or mechanics in general, just the nature of the beast with electrical systems any less robust than a 25kV utility substation.

 

[Topper]

No upside, all downside.

Point taken. I was thinking the upside was finding the problem now and not having it show up again. I think you are right, I will wait and see if it is an ongoing problem before having them look at it and possibly creating a new one.

Thanks!

Jim

 

[wsuffa]

Dont do it ! Dont allow them to touch it.

You said this:



At this point, there is no improvement possible beyond the thing holding your altitude if you depress that engage switch.

No upside, all downside.

Many tales of woe started with a tech 'giving it a quick look'. Pins get bent, litttle springs get unsprung, retaining screws get lost etc. That is not an attack on the particular tech or avionics techs or mechanics in general, just the nature of the beast with electrical systems any less robust than a 25kV utility substation.

I would give the same advice. I have had more trouble with avionics shops than Any other service provider.

Sent from my DROID RAZR using Tapatalk 2

 

[JHW]

So did you identify the purpose of the fuse you changed? If it is for some piece of equipment long since removed, you might have just created a stray hot wire. If it can't be identified and everything worked without it, I would be inclined to re-remove it until you can sort it out.

 

[Topper]

So did you identify the purpose of the fuse you changed? If it is for some piece of equipment long since removed, you might have just created a stray hot wire. If it can't be identified and everything worked without it, I would be inclined to re-remove it until you can sort it out.

Yes, sort of. I left that part of of the story since it did not affect the autopilot. It was dark when I was looking at the battery and noticed the fuse holders. After figuring out it was not for the auto pilot, I took a much closer look. I wanted to know what was not working! There are two fuses above the battery. One is for the clock and the second one (the one that was blown) powered a small very short male pin next to the fuse holder. I assumed it is for power to test something, but I am not sure. If no one can identify if from my description, I will take a picture.

Thanks,

Jim

 

[Skylane81E]

FWIW the fuses you found are for the external power jack and the clock

 

[jsnapp]

I would not have the avionics shop do anything unless the problem returns. For the stec-30 the pitch computer and roll servo in the back are almost stand alone. The first thing to always try is to disconnect the D connector into the pitch computer and servo and reconnect and see it that fixes it. If it does there is a god chance it will continue to work. Only if it returns should you go further.

 

[Topper]

FWIW the fuses you found are for the external power jack and the clock

One fuse was the clock and the other may have been labeled power jack. What is the power jack? It appears to be wired to a pin next to the fuse. Not sure what this would be used for.

Jim

Thanks for the replies. I will leave it alone as long as it keeps working.

 

[Skylane81E]

Jump starting jack

 

[gismo]

Jump starting jack

I don't have a Skylane wiring diagram but I doubt there's any fuse involved in the External Power connection. There's usually a diode in between the small pin and the coil of the reverse polarity protection relay but I've never seen an installation on a piston single that included a fuse there and the diode is likely to open before a fuse anyway. Perhaps the other fuse was for a 12v cigar lighter type outlet inside the cabin?

 

[Skylane81E]

I don't have a Skylane wiring diagram but I doubt there's any fuse involved in the External Power connection. There's usually a diode in between the small pin and the coil of the reverse polarity protection relay but I've never seen an installation on a piston single that included a fuse there and the diode is likely to open before a fuse anyway. Perhaps the other fuse was for a 12v cigar lighter type outlet inside the cabin?

On the third pin IIRC, but yeah, I've chased the wire myself.