Motocycle intercom. Faulty POT

[RMIM]

Hi Everyone,

I just bought a motorcycle intercom off ebay (starcom1 Digital - TheRange). I decided to modify the remote (volume control).

The volume control is just a pot on a cable with a 3.5mm jack on the other end that plugs into the intercom unit. The white wire is connected to one side of the pot. The bare wire is connected to the common. The red wire is connected to a 1k resistor which is then also connected to the common (so only 2 terminals of the pot are being used).

The unit is digital - the sound does not actually travel trough the pot. When you vary its resistance, the electronics translates this and alters the vol accordingly (I think).

The mod I made was just to make the cable shorter. It was working fine for days. When I turned the pot the sound would turn up and down very smoothly. Now for some reason the sound is very jumpy. It can go up or down when you turn the vol up.

I though it must be my soldering - so I tried to fix that. It's the same. After many hrs I decided to put the blame on the pot itself. I had a tiny trimming pot that was also 10k - it seems to be ok with that.

I found the original pot on the web
**broken link removed**
I believe it's the PC16ECO. The first one in the pic

I have just bought the following as a replacement
Bourns | Passives | Resistors, Potentiometers or Control Knobs | Resistors, Variable Panel Mount | Conductive Plastic

Bourns | Passives | Resistors, Potentiometers or Control Knobs | Resistors, Variable Panel Mount | Conductive Plastic


My question is, is the pot I have bought a better pot than the original? How much is the original? Where can I get one? (I don’t really want to buy one from starcom, it cost 25pounds, Im sure you are just paying for the cable/housing etc which I put in the bin anyway).

Or perhaps the problem is not with the pot? What is the red wire and 1k resister for? If I leave it off it still seems to work?

Thanks.

 

[Boncuk]

Hi RMIM,

from your description the pot is wired like this: (attachment)

So all three wires are used and the 1K resistor combined with the pot makes a voltage divider.

There are only two possibilities for a malfunction: either your solder job wasn't good or the wiper of the pot (connected to the axle) didn't stand the stress of turning (with side pressure) and therefor the wiper doesn't contact the carbon resistance trace at all times.

You can veryfy the latter by connecting the pot to a voltage source of 1.5V.
Connect + to the terminal (white) and - to the terminal (bare). Slowly move the pot from one end to the other and observe the voltage reading at the center tap. The output voltage should slowly and steadily increase or decrease with rotation. If there are jumps in readout you should replace the pot.

Boncuk

 

[RMIM]

Thanks for the reply Boncuk.

You misunderstood me for the wiring.
The white wire is on PIN 2 as per your diagram.
The bare wire is on PIN3
And the red wire is on a 1k ohm resister. The other side of the resister joins bare wire on PIN3

PIN1 is not used.

I will try your pot test. I have found that if I push on the POT it seems to make the sound jump.

My new pots should come tomorrow - hope I bought ones that will do the job. I did see some other ones that were called precision pots that cost a lot more, but still affordable at 10pounds - should I have bought that? I did some reading and I found out that conductive plastic were the best kind to get for audio.

 

[Boncuk]

Thanks for the reply Boncuk.

You misunderstood me for the wiring.
The white wire is on PIN 2 as per your diagram.
The bare wire is on PIN3
And the red wire is on a 1k ohm resister. The other side of the resister joins bare wire on PIN3

PIN1 is not used.

I will try your pot test. I have found that if I push on the POT it seems to make the sound jump.

My new pots should come tomorrow - hope I bought ones that will do the job. I did see some other ones that were called precision pots that cost a lot more, but still affordable at 10pounds - should I have bought that? I did some reading and I found out that conductive plastic were the best kind to get for audio.

Hi RMIM,

that kind of wiring doesn't make any sense to me. If the wiper is left unconnected you might as well skip the pot. So please recheck the wiring.

The pot should not have any slack in vertical direction. I'm almost sure it is broken.

No matter if the resistor material is carbon or conductive plastic. Both of them are pots. Might be conductive plastic has less wear and tear.

Boncuk

 

[RMIM]

Hi RMIM,

that kind of wiring doesn't make any sense to me. If the wiper is left unconnected you might as well skip the pot. So please recheck the wiring.

The pot should not have any slack in vertical direction. I'm almost sure it is broken.

No matter if the resistor material is carbon or conductive plastic. Both of them are pots. Might be conductive plastic has less wear and tear.

Boncuk

Well you are right, it does not have to be a POT in the circuit (3terminals) - it would work with a variable resister (as they are only using 2terminals)

I'm very sure the circuit is right. I too find it strange, that's why I asked about it - but it does go to a unit that is digital, so it could do something (trouble is when I left it off the remote still seemed to work). Or is the red wire something to do with suppressing interference?

I'm sure the circuit is right as the remote is the original remote made for that intercom. When I took it apart it was like that and had the red wire with 1k resister shrink wrapped together with the other end of the resister on the same terminal as the bare wire.

I have installed the new pot, and all seems fine. I hope I dont have to replace that one any time soon.