dabigboy

Howdy all,

I ran into a really weird problem the other day. I have an old Futaba Conquest 4NBF radio. Some time ago, the elevator channel failed. I think I tested it (forget how, guess I swapped rx crystals and tested with another rx), and decided it was the TX that's bad. I'm not sure if I want to try to fix it (by replacing the elevator potentiometer, if that's the problem), or convert it to simulator use........anyway, I took it apart to have a look at things. Strangely, when I test the potentiometers, I'm getting no resistance! I tried several of the potentiometers in addition to the one that might be bad, and I'm just not seeing any chage in resistance as I move the pot. It always shows zero resistance. I tested all three terminals, no two of them result in anything other than an open circuit.
Are these some kind of "special" potentiometer? I'm used to the PC joystick variety. I'm testing on the solder points on the small bit of wafer board attached to the pot.

-Matt Bailey

olivier

Hi,

All modern transmitters are using a 4.7K-Ohm potmeter (linear of course). But to find such a physical size of potmeter is vey difficult. Mostly it's not the standard-size of body or screw-threat (if any), mostly the turnhandle is partly flattened (can be done with a file.
).
But for your problem of a potmeter having no resistance, that's weird. I do not dare to ask you, but I really suppose you know how to use your multimeter. But possibly that no resistance is encountered whilest the potmeter is connected to the circuit-board.

Olivier

dabigboy

Actually I'd tried running TX potentiometers straight into the PC gameport once.......I didn't think it would work, and it didn't. Range was weird. But it did behave like a potentiometer. I may be able to make it work now though, as I have a USB interface module designed for handling various types of position-sensing devices. It's somewhat of a long shot, but I figure it's worth a try. Interesting that you mention the physical dimensions of the pots being odd.......I always figured they were a bit non-standard. But as it happens, I have two pots of suitable resistance (out of an old set of racing pedals) that are identical! Between these two sets I should be able to come up with a part number or something (or I might be able to go by dimensions....mouser.com has a ton of stuff like this, with full specifications).

Yeah I know how to use the meter, but thank you for your concern. I've been playing with these interfaces quite a bit recently and currently have some 100k slide pots doing duty in full-size homemade controls for PC flight simulation. I'm sure I've tested every possible way of connecting the pots. The circuit board thing occurred to me too, so I snipped the wires to the pots in one gimbal. No change. The only thing I can figure is that somehow these two pots have become shorted out (maybe there's enough dirt in them that it provides an electrical bridge, LOL........I *do* have a fair amount of metal shavings in my shop ). I've yet to check the other pots. I guess the next thing to try is to take a closer look at the pots themselves.......and check everything again (who knows, maybe I was sleepy that day).

Thanks for posting.

-Matt Bailey

A. J. Clark

Gee dabigboy your really confusing me


could you give us another shoot. Are they open or shorted??

A. J. Clark

dabigboy

Ermmm, shorted. Sorry for the typo, I should have said "no two of them result in anything other than a *closed* circuit." Not enough sleep......


-Matt Bailey

A. J. Clark

Well I don't have a definite answer. Like Olivier said shorted is odd especially two of them. I would look at the meter. Test it against another one. Or put another resister in line with the pot and see what you get.


A. J. Clark