Bad potentiometer can't measure value. - Page 1
Forum section: electronics / repair

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: October 14, 2018, 04:06:03 pm
content: I have a 2.1 sound system for my PC that has a volume knob that jumps around all the time so I am almost 100% sure I need to replace the potentiometer however, the value has almost been wiped off the body and getting an accurate reading on my DMM is impossible since the resistance value keeps jumping all over the place so does the volume when listening to music.I have attached a picture below for your reference and please note that there is a off switch integrated as well.How can I get a replacement for this part if I can't read or measure its resistance?

author: commongrounder
author_rank: Frequent Contributor
timestamp: October 14, 2018, 05:00:52 pm
content: You should be able to get a stable resistance reading if you probe the outer two legs of the pot (not the extreme outside switch legs, of course). The center pin connects to the wiper, which will give an unsteady reading if it is dirty or damaged. What may be hard to tell is the taper. I suspect it’s a digital controller, since it is a single section pot. That could be linear. A pot that carries audio is almost always log.Have you tried treating it with a pot cleaner, like Faderlube? It may just be contaminated, and cleaning would help clear that.

author: DaJMasta
author_rank: Super Contributor
timestamp: October 14, 2018, 05:47:12 pm
content: Are you sure it's a potentiometer? Could be a rotary encoder, they can be in similar packages but I feel like that package suggests that to me, and they do come in 3 pin with stabilization connections.If you can get something under it, there also may be a part number on the bottom side, which could tell you all you need to know to get a replacement. If there's no easy way to say, removing it may be a reasonable course of action since it's likely going to be replaced anyways.

author: ataradov
author_rank: Super Contributor
timestamp: October 14, 2018, 05:49:01 pm
content: Of if you can't read or measure the resistance, assume it is 10K. It is a pretty safe bet in most cases dealing with audio.How to fins a replacement part is a whole different story.

author: ataradov
author_rank: Super Contributor
timestamp: October 14, 2018, 05:50:25 pm
content: Quote from: DaJMasta on October 14, 2018, 05:47:12 pmIt is a potentiometer. That dimple in the case looking right at us is the limiter for the wiper.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: October 14, 2018, 06:47:40 pm
content: I only assumed it's a potentiometer because it looks like one.Anyway I have removed the unit and as can be seen in the picture below, there is only a VR2 which I assume stands for Variable Resistor 2.I measured the resistance between the two outer pins and it's at 49K Ohms.

author: SeanB
author_rank: Super Contributor
timestamp: October 14, 2018, 06:59:25 pm
content: So a nominal 47k B taper ( audio taper, not linear A taper) pot, very common to find.

author: commongrounder
author_rank: Frequent Contributor
timestamp: October 14, 2018, 07:06:15 pm
content: SeanB, you can’t assume audio taper. A single section pot controlling multiple audio channels hints at VCA control.It also could be a 50k value. If you can get a reading between one of the outer legs and the center leg, with the pot turned as close to half way around it’s rotation as you can, you should get a hint as to it’s taper. If the reading is right around 25k, it is a linear taper pot. Any other taper will be a good bit higher or lower than that, depending on which outer leg you choose.

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 14, 2018, 07:19:31 pm
content: So a 50K pot is a very common item. However finding one with exactly that mechanical configuration will be quite difficult, IME.You would be FAR FAR ahead of the game by trying to clean the pot. Finding replacements for weird mechanical pots like that is a nightmare.Since it is a single section pot, and your "sound system" is 3-channel ("2.1"), it is almost certainly creating a DC voltage relative to the knob position and the gadget is using some other method to actually control the audio volume. There is no way that pot is actually controlling the audio signal directly, so it is very UNLIKELY to be a log/audio taper pot. It is almost certainly a LINEAR pot.OTOH, since it is only creating a DC voltage, the actual resistance value of the pot is of almost no significance at all.I wouldn't want to use anything lower than 5K ohms or higher than 100K ohms. but anything in that rough range would likely work fine.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: October 14, 2018, 07:32:37 pm
content: I have taken the pot apart by moving the three tabs out of the way and moving the metal body upwards as much as possible, applied a liberal amount of contact cleaner and put it back together.Now I am getting a steady resistance change from 5 Ohms to 49 K Ohms.I have soldered the pot back on the board and will try it out to see if I have solved the issue.

author: drussell
author_rank: Super Contributor
timestamp: October 14, 2018, 07:58:40 pm
content: Quote from: SeanB on October 14, 2018, 06:59:25 pmUsually "A" taper is the logarithmic/audio taper and "B" is linear.It is getting difficult to find audio taper pots, especially the dual stacked ones. Luckily your application is almost certainly linear (and is a single) if you do end up needing to replace the pot but it will likely work just fine after a good cleaning.

author: coromonadalix
author_rank: Super Contributor
timestamp: October 14, 2018, 08:05:19 pm
content: Sometime you can dismantle the pot body and put back the holding 2 pins base into a new one if you do it carefully.Done that in the past, worked very well.

author: floobydust
author_rank: Super Contributor
timestamp: October 14, 2018, 08:14:23 pm
content: To figure out taper, just turn the pot to the middle and measure resistance.

author: coromonadalix
author_rank: Super Contributor
timestamp: October 15, 2018, 01:32:55 am
content: here is an simple drawn overlay in blue schematic of your potentiometer on the pcb

author: vk6zgo
author_rank: Super Contributor
timestamp: October 15, 2018, 10:36:57 am
content: Quote from: drussell on October 14, 2018, 07:58:40 pmBack in the day, in Oz, linear was "A" curve, & logarithmic was "C" curve.Seemingly, it was the same in South Africa, & probably the UK.

author: drussell
author_rank: Super Contributor
timestamp: October 15, 2018, 01:59:04 pm
content: Quote from: vk6zgo on October 15, 2018, 10:36:57 amHistorically, that was true but most replacements you will find now are the opposite, though exceptions most certainly still exist and local production, especially of high-end potentiometers may use different variations. It pays to double check before you just grab any ol' pot.The traditional suffix lettering:

author: Jwillis
author_rank: Super Contributor
timestamp: October 16, 2018, 06:17:19 pm
content: Creative Labs I-Trigue 3400 PC speaker system?I found this schematic .The big question mark is in reference to the pin outs for the socket. Hope this helps.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: October 19, 2018, 11:36:31 am
content: Thanks for recommending cleaning the pot guys! It is back to working perfectly and I'm glad I don't have to spend hours on the aliexpress trying to find a replacement!

author: kaancol
author_rank: Newbie
timestamp: April 17, 2023, 06:43:31 pm
content: hi guys have the same issue i pull it out and now i dont know how to connect the right pin with the right cable port to 9pin. i found for creative T3100 but not the same color pins... i have the 3400 i don't want to burn it..