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[kiwimodeller]

Greetings all, I provided the entertainment at a recent sailing day by falling in the lake fully clothed and with my cellphone in my pocket and my Spektrum DX5e transmitter on a lanyard around my neck. Didnt score many points for style I can tell you! After drying out most things have come right except for one function on the transmitter which only moves the servo very slightly in one direction and not at all in the other direction. After checking that the servo works fine when plugged in to another port in the receiver I sent the transmitter back through a dealer to the importer to see if the one function could be repaired. The answer came back that they do not do repairs, they send them back to the maker or would do except that would cost more than a new transmitter. When I asked for a price for the new transmitter I was then informed they only sell Tx and Rx as a pair unless I order the Tx on indent and wait some time for it to arrive. In frustration I got the thing back and took the back off to have a look myself. It is obvious that each stick function moves a Potentiometer and I am thinking that the throttle pot has been damaged by water. My questions are :-
1) How does one test them, is it just a matter of measuring resistance as the shaft is rotated either side of the centre position?
2) How does one buy a replacement? The only markings are the letters HY in a circle and B12K on a sticker. Does this mean anything? Obviously physical dimensions need to be the same but so too do the internals. I am capable of disconnecting the three small wires and soldering them to a new Pot if that is what is needed. Any advice most welcome. Cheers, Ian.

[tr7v8]

If it is an open pot, it might be worth squirting some contact cleaner into just that function to see if it helps.

Loads of Tx only on E bay one for £35 +£5P & P.

[malcolmfrary]

Big problem would likely be getting a physically identical one to be able to fit it mechanically.  Another potential problem is being able to dig the existing one out - I haven't seen inside one of these, but the trend these days is to use cunning and subtle mouldings to make repair more difficult.The B12K could refer to the value - 12K and the B could meant its linear rather than log.  Or not, that's not a common value.  Maplins do have a range, and the on line catalogue does have pictures.
With the power off, I would measure one of its mates, then check the suspect.  Connect the resistance meter to one end tag and the wiper, move the stick, note the readings.  The potentiometer circuit doesn't just consist of the pot - there are components at the other end of the wire, there might be a bit of nasty growing on one of them.

[Corposant]

Ian

It would be surprising if water has caused "irrepairable" damage to the pot. As Tr7v8 says, switch cleaner should do the trick if it can be got to the problem area. Malcolm points out that replacing the pot. may not be feasible but you say you could disconnect the wires. In my opinion this would be worth doing because you could then check its function with a multimeter, independently of other components. (Also find its value and whether its linear.) If it's okay, then the problem lies elsewhere - and you're in trouble!

Mike

[Netleyned]

If you have an unused stick axis then swapping the pots coulld prove the answer

Ned

[Martin (Admin)]

I suggest a can of 'safety solvent, - http://www.maplin.co.uk/electronic-solvent-cleaner-30056

LIBBERALLY wash a can of this through the back of the transmitter, gymbols... everything, leave it to dry overnight and see it works then.
( In a case of a Ribeana spill in my own laptop...

1.   Shout at the kids!
2.   Remove power and batteries as quick as possible.
3.   Strip down laptop to see how bad the damage is... it's bad!
4.   Shout at the kids again!
5.   2 hours to remove system board.
6.   Wash system board in washing up bowl and mild green Fairy liquid. ( my hands are lovely and soft! )
7.   Shake dry as much as possible.
8.   Drown system board in Safety Solvent to wash away and water residue.
9.   Leave to dry for 24 hours.
10.   Rebuild laptop.
11.   Laptop works
12.   Shout at the kids again!

[kiwimodeller]

Thanks for all the ideas. Tonights effort was to remove the pot (not diificult) and spray CRC electrical contact cleaner in to the only small opening I could find in the housing while turning the shaft back and forth. I decided to see if the servo now functioned properly so switched both Tx and Rx on and twisted the Pot back and forth. To my joy the servo seemed to have full travel, perhaps even more travel than usual. I then reassembled the Tx only to find that I am back to having only a tiny amount of travel!!!xxx! To double and triple check I then plugged another servo in but it barely moved either and when I plugged the original servo in to an unused channel it seems to work as it should. I will leave it there for now while I have a think about what to check next. Cheers, Ian.

[Corposant]

By and large very encouraging! There has to be a simple explanation - all you have to do is find it! "Have a think" - that's a good idea!

Did you have to unsolder the wires to get the pot. out? (The implication being that there have been four heatings of the solder tags.)
The next thing to do would be to repeat the exercise, without using switch cleaner and see if the pot. still works outside the case and if it does, investigate carefully what happens while it's being re-mounted. If it doesn't work outside the case, does switch cleaner cure it again?

Just my thoughts on the matter. 

Mike

[funtimefrankie]

On my transmitter there's a switch which restricts the movement of servos, I forget what it's called. Sometimes this gets knocked by accident, and I have a moment thinking there's a fault, then I remember and de-switch...
Just a thought................

[Martin (Admin)]

" Dual Rates"
 http://www.modelaircraft.org/mag/FAQ/answers/faq-q27.htm

[kiwimodeller]

Thanks again, I did not have to disconnect the wires to get the pot out. The idea of swapping a pot from an unused channel has occured to me but I would like to repair the set back to original if I can. If that is not possible then I will consider swapping. At the moment my thoughts are that the pot is somehow damaged in the center part of its motion but I will take it out again and do a more careful check of its operation. I got too enthusiastic last time when I saw the servo operating and put it back in without a thorough check. I will be going to the city sometime soon so will also call at a couple of electronics stores and see if I can get a replacement Pot. Will keep you posted. Cheers, Ian.

[dodgy geezer]

"... Tonights effort was to remove the pot (not diificult) and spray CRC electrical contact cleaner in to the only small opening I could find in the housing while turning the shaft back and forth. I decided to see if the servo now functioned properly so switched both Tx and Rx on and twisted the Pot back and forth. To my joy the servo seemed to have full travel, perhaps even more travel than usual..."

So you are saying that when you rotated the pot with your fingers everything worked, but when you attached the stick it didn't? At least you have shown that the electrics are fine, and the problem is physical...

I think there are only two possibilities now. Either the stick is not clamping properly to the pot, or (more likely) the spring contacts inside the pot are not touching the track with sufficient pressure, and when you hold it in your fingers you are pushing (or pulling, depending on design!) the central shaft in or out, and making better contact.

Pots are pretty standard items - lurk on some electrical sites and I think you're bound to find a match. I have occasionally tried to mend electrical components by disassembling them and bending or replacing internal parts, but it has rarely been entirely satisfactory...