Help finding vintage potentiometer - Page 1
Forum section: electronics / projects

author: Skyfox
author_rank: Regular Contributor
timestamp: February 09, 2018, 07:48:34 pm
content: Hi all,My project is replacing the volume control potentiometer in an old radio (70s or early 80s). It was having the problem of making a lot of static crackle over the speaker when adjusting volume, so apparently corrosion or something is making it wear out. In my parts bins I found a nearly identical replacement, but that one also has the same problem, just to a lesser extent. So I figured I'd just get a brand new one and replace it for good since the thing is apart. Easy, right?Wrong. I can't find this style of variable resistor anywhere. The old one is an Alps brand 10K pot, and the only part number on it is 32Z. I can't find anything on that part number at all, and the Alps website doesn't have this style any more. I've attached a pic of the specs. It has a 15mm D-style shaft, through hole pins perpendicular to the shaft, and the big snap-in lugs on the side for securing to the board.I've looked through Digikey, Mouser, Jaycar, Full Compass, Banggood, Tayda Electronics, Radio Shack (which is a joke any more), and whatever other sites I could find and turned up nothing for any pot that matches this size and shape. I've found somewhat similar pots with the pins on the front side of the body (the face where the shaft comes out) instead of the back side like this one, but that won't work because there's almost no clearance behind where this thing mounts on the board to have one with the body on the opposite side of the pins. Any ideas where to find one?

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: February 09, 2018, 07:54:35 pm
content: If a replacement has the same problem, and a shot of Deoxit doesn't fix it, look for a slightly leaky coupling cap. Even a tiny amount of DC on a volume pot will cause that problem.

author: Skyfox
author_rank: Regular Contributor
timestamp: February 09, 2018, 11:29:17 pm
content: The only cap I found that looked questionable was down by the power plug connection. I didn't know if it was leaking or had glue residue on it, so I removed and tested it. Two testers showed it was just fine, within 10% of rating, so I put it back in. The board has very few electrolytics on it, and they all look fine.I don't have any Deoxit on hand, so the next time I do a parts buy that'll be on the list.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: February 10, 2018, 04:55:40 am
content: Most testers won't show the problem. You have to measure microamps with operating voltage applied, so it's usually better to just replace them.

author: Cyberdragon
author_rank: Super Contributor
timestamp: February 10, 2018, 05:34:29 am
content: You need a capacitor tester with ESR and leakage testing to properly test caps.

author: Skyfox
author_rank: Regular Contributor
timestamp: February 10, 2018, 01:25:15 pm
content: Capacitors aside, does anyone know where to find an older style variable resistor like the one in the picture?

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: February 11, 2018, 05:30:47 pm
content: Old pots, especially with loudness taps, are getting hard to find. My best source is hamfests during the summertime. Or, find junk items at Goodwill or the dump and strip them out of those. A few surplus dealers sometimes have pots. Tryhttps://www.tubesandmore.com/

author: Paul Price
author_rank: Super Contributor
timestamp: February 11, 2018, 05:57:04 pm
content: In my experience with this scratchy pot problem, I've found:(1)Just the tiniest 1/10 Sec shot of WD40 will fix this problem, also helps to perform step two afterwards.(2)In some cases rotating the pot from end to end of rotation about a hundred times will also remedy this problem.(3)If there is a D.C. bias on the pot, you can measure it at the center tab of the pot with a DVM. If there is D.C. present, you can jerry-fix the problem by cutting the trace at the wiper pin of the pot and inserting a series electrolytic capacitor to block the D.C. component.(4)All of the above.