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Electronics => Repair => Topic started by: fritterandwaste on January 17, 2022, 12:15:08 pm

Title: Repair faulty pot
Post by: fritterandwaste on January 17, 2022, 12:15:08 pm
Hi. I have a number of guitar pedals which appear to have faulty and/or noisy pots. I have been looking at one in particular which, in live use, displays the symptoms "off or on full" with only 100% increase available. I have taken the pot apart and what I can see of the carbon (?) track appears to be in good condition yet when I place a multi meter at any two separate points on the track, I appear to have no circuit when I'd expect to have one. Is this a valid test that, if conducted at various points and distances on the track, proves that the track itself is operational (I am at the beginner end of the electronics scale) and, if so, can anyone offer any suggestions as to how to resolve the problem or a way to establish that the pot needs to be replaced.

Thanks in advance.
Title: Re: Repair faulty pot
Post by: TheMG on January 17, 2022, 02:13:11 pm
Deoxit Fader F5

Spray it in the pot, work the pot back and forth a few times, and voila just like new!
Title: Re: Repair faulty pot
Post by: CaptDon on January 17, 2022, 04:46:43 pm
If it only gives you 0%/100% with nothing in between the pot may be open circuited on the hi (not ground) side. The carbon track becomes disconnected from the metal terminal where the wires are soldered. At 'full throttle' (name of a local band B.T.W.) the wiper hits the metal terminal and you get 100% volume. This happens a lot with pots. It may be un-repairable but replacement pots are easy to get and easy to install. When your reputation is on the line during a gig (Tune it or die!!  Remember that T-Shirt?) Just replace the pot and sleep better knowing you won't be "That guy" who brings questionable unreliable gear to the gig!!! (Like my keyboard player who owns the biggest pile of unreliable keyboards and sound gear!!!! It is a shit pile that goes together like a Tinker-Toy set with half the pieces broken or missing, but he won't let me bring my gear which mostly came from the Clair Brothers used gear warehouse and is in superior condition. He is a control freak and it is 'his' band.)
Sure wish I still had my ShoBud volume pedal given to me by a steel guitar player. I have an Ernie Ball now.
Title: Re: Repair faulty pot
Post by: Gyro on January 17, 2022, 05:19:03 pm
I'd suggest using conductive plastic pots as replacements, they tend to more rugged, longer lasting and smoother operating than Carbon ones.
Title: Re: Repair faulty pot
Post by: Hamelec on January 17, 2022, 08:29:24 pm
wat 20 years, then post again  ;)
Title: Re: Repair faulty pot
Post by: fritterandwaste on January 18, 2022, 11:16:13 am
Thank you all.

Captdon: Understood on track losing connection with contact but shouldn't I be able to put the two DMM leads at different positions on the track itself and get a circuit? That's kind of what's throwing me on this especially as there are no visible issues. Agreed re gigs. I can't see me using this pedal live (I am migrating to Guitar Rig 6 software instead as there's so much that can go wrong with pedals in general and I'm rarely happy with the sound I get). It just mught be fun to use it at home occasionally and I'm also delving into electronics as a bit of a hobby so potentially killing two birds with one stone (NB two band names in there sort of!)

TheMG: I actually ordered some WD40 Contact Cleaner last night. Hope that's as good as the Deoxit.

Hamelec: Sadly I may not live that long!
Title: Re: Repair faulty pot
Post by: Audiorepair on January 18, 2022, 11:48:52 am
Yes, you usually can put a meter directly on the track and measure its resistance, I can't see how that is not working for you unless your meter is on a low ohms setting.

Before you get lots of abuse about using WD40 as a contact cleaner, I suspect (hope) you have ordered "contact cleaner made by the company WD40".

Otherwise this is good stuff at a fraction of the price of De-oxit:
Didn't notice a great difference when I switched to De-oxit.
Title: Re: Repair faulty pot
Post by: fritterandwaste on January 18, 2022, 12:50:30 pm
Thanks. I had the DMM set simply to beep when circuit complete so quite strange. Yep definitely (WD40) contact cleaner - I have become very much aware of the two WD40 camps in recent research. :)
Title: Re: Repair faulty pot
Post by: m3vuv on January 19, 2022, 10:49:15 am
had a friend with a renault aventine,the throttle position sensor pot was worn out,a replacement was about £300 as it was a part of the throttle servo motor,after removing the cover i couloured in the carbon tracks with soft HB pencil,reset the dtc fauld codes and it ran ok for about 3 months,i guess the carbon from the pencil filled any cracks in the pot tracks,ok not the best solution but it needed doing every couple of months!,maybe an option as a temp fix on noisey pots tho.
Title: Re: Repair faulty pot
Post by: fritterandwaste on January 21, 2022, 09:54:50 am
Thanks, I gave that a try. No joy I'm afraid. I'll try and source a new pot. Any suggestions for suppliers would be gratefully received.
Title: Re: Repair faulty pot
Post by: CaptDon on January 21, 2022, 05:06:43 pm
Try to measure the pot end to end. You should see typically around 50k ohms. If you see a sensible resistance from end to end (10k or more, but less than 100k) then the element is o.k.  Next put your meter between the high side of the pot and the wiper. As you 'increase' the volume pedal you should see decreasing resistance down to just a few ohms or less. I did have a guy with a volume pedal problem similar to yours. His pedal was actually good but he was feeding into a very low impedance (150 ohm microphone terminator) circuit and the pedal appeared dead except at max. Am I correct to assume this is a passive pedal with no batteries or external power supply like my Ernie Ball or ShoBud?

Title: Re: Repair faulty pot
Post by: fritterandwaste on January 21, 2022, 06:36:14 pm
Thanks. This is actually a Pro Co Rat effects pedal that does take a 9V battery. This pot is for the volume (2 others for distortion and filter). I will try what you suggest but, as I can't get a reading between two points on the wiper track, I don't hold out much hope.