Beginner needs help with componant.

[Dr Stoppage]

Hi

Can anyone help me with this part. It's a rotary potentiometer. It was used in the speed control circuit of a Dremel (clone) rotary tool. Over a long period it started to become nu-responsive and is now open circuit. When I de-soldered it I thought I saw the number 4701 printed on it but when I removed dust that was covering the part it removed the number. It measures 11mm x 10mm with a shaft length of 6mm.

As I can't measure the value can anyone tell me the likely resistance of this (10k? 50k?) also can anyone tell me the model type please.

Thanks for any assistance.

 

[KeepItSimpleStupid]

You can try cleaning with contact cleaner, but if you can;t measure the end to end resistance, the element can be cracked.

It doesn;t look like a rotary encoder.

here:

is a typical speed control or dimmer.

If it's bad, you can always take it apart and see if you can salvage or fix anything,

Failures are ususlly:
1. worn spot
2. Particulate accumulation
3. spring tension on the wipers
4. Broken element

Nonetheless, you should be able to determine the value after you have it apart.

Pitch is going to be important too. Easiest way is to take a pic with a ruler on the same plane and in line with the pitch to be measured..

Now you can optically measure with ratios.

 

[Diver300]

4701 is likely to mean 4700 Ohms (470 and 1 more zero).
Something like this https://www.digikey.ca/product-detail/en/bourns-inc/PTV09A-4225F-B502/PTV09A-4225F-B502-ND/3781158 would be a close equivalent, but I'm not sure about the shaft length.

 

[Nigel Goodwin]

I agree with Diver300, looks like 4.7K from the number given - I'm presuming it's a low voltage tool?, and not a mains one which KeepItSimpleStupid was assuming.

Physically it looks like a sort of pot you often see in things, but never seem to see them for sale anywhere?.

 

[JimB]

As I can't measure the value

Try this trick:
Turn the shaft of the pot so that it is at half travel.
Use your DMM to measure from the slider (centre pin) to each of the end terminals.
If the fault is at one end of the potentiometer track, you should be able to measure half the total resistance value from the slider to one end of the track.

JimB

 

[Nigel Goodwin]

Try this trick:
Turn the shaft of the pot so that it is at half travel.
Use your DMM to measure from the slider (centre pin) to each of the end terminals.
If the fault is at one end of the potentiometer track, you should be able to measure half the total resistance value from the slider to one end of the track.

JimB

Assuming it's a linear pot?, but neat trick though.

 

[JimB]

Assuming it's a linear pot?

True.
But in an extreme case you could always get out a protractor and plot several resistance values vs angular rotation....


JimB

 

[gophert]

In general, a 5k should work just fine if it was a 4700.

this one looks pretty close...

PTV09A-4015F-B502 Bourns Inc. | Potentiometers, Variable Resistors | DigiKey

Order today, ships today. PTV09A-4015F-B502 – 5k Ohm 1 Gang Linear Through Hole, Snap In Potentiometer None 1.0 Kierros Carbon 0.05W, 1/20W PC Pins, Board Locks from Bourns Inc.. Pricing and Availability on millions of electronic components from Digi-Key Electronics.

www.digikey.com

 

[Nigel Goodwin]

In general, a 5k should work just fine if it was a 4700.

this one looks pretty close...

PTV09A-4015F-B502 Bourns Inc. | Potentiometers, Variable Resistors | DigiKey

Order today, ships today. PTV09A-4015F-B502 – 5k Ohm 1 Gang Linear Through Hole, Snap In Potentiometer None 1.0 Kierros Carbon 0.05W, 1/20W PC Pins, Board Locks from Bourns Inc.. Pricing and Availability on millions of electronic components from Digi-Key Electronics.

www.digikey.com

5K and 4K7 are the same thing, well within each others tolerances - and tolerances on pots are pretty crappy anyway (not that there's any need for better).

I've been using some 0.5% resistors recently (as the 1% were out of stock), even more confusing, I thought brown tolerance bands were bad enough!

 

[dr pepper]

Bend the tabs back and have a look inside it, might be something you can do to get it to work again, maybe for a while at least.