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Suggestions how to repair these

I have a pair of JPW Powered Monitors (1995), Made in UK, perhaps in one of the last production batches before the company was acquired and moved production in the Far East. Bought brand new for a PC-based audio back then but used it intermittently for couple of years only and stored them for several years in its box. Took them out recently and I'm still amazed at their soundstaging and imaging particularly if mated with a sub. I really like them a lot. However, a couple of things need to be fixed.

1) The volume pots are stuck at 9 and 10 o'clock positions and don't move at all. For now, however, I'm using the source's volume control but eventually I'd like the source at full volume and adjust the speaker's volume controls. What caused it to get stuck? Is this a common occurence when left unused for long periods? Is this something I can repair myself or should I just bring them to a qualified technician? What needs to be replaced here (or cleaned)?

2) White spots/residue (not dust) have developed around the baffle and cone areas. There's no effect whatsoever on the sound but I'd like to remove and clean them. Can you suggest the best and safest way to do this? Any specific cleanning material?

For visual reference, please take a look.

Everything else are perfect - cabinet, grills, etc. are spotless and clean like new. Sound quality, as mentioned, is spectacular. But these two things bother me and would like them fixed. Any helpful suggestion or recommendation would be greatly appreciated. Thanks.
edgejazz
5 responses Add your response
edgejazz OP
46 posts
 
Thank you, Richard. The shaft of the pots are metal but I'll try your suggestion too. I plan to work on it over the weekend.
palasr
526 posts
 
If they're stuck, I would spray them lightly with a tiny amount of silicone based lubricant first before I got out the contact spray, especially if the shafts of the pots are plastic. Many plastic shafted potentiometers will literally melt from exposure to certain types of solvents, especially those used in spray contact cleaners. Plastic shafted (and conductive plastic element) potentiometers are best cleaned and lubricated with Caig MCL, a goopy blue spray designed for the task. Either way, use way less of any type of spray than you initially think - a tiny little dab will do.

-Richard
edgejazz OP
46 posts
 
Thank you, Mcfarland and Mr.M. I think I can handle the cleaning and that sort and if it doesn't work will send to a technician for replacement.
m297904
93 posts
 
For a pot to be THAT gummed up that it is stuck sounds like it MAY be past the point of repair. That being said, you have nothing to lose by trying to clean it with contact cleaner. It looks like the easiest way to get to them is to remove the woofer. Saturate the pot with contact cleaner as McFarland mentioned. LET IT SOAK, then saturate it again and MAKE IT TURN. You have nothing to lose because if you can't make it turn, you will replace it with a new pot that you can get from Digikey or Mouser or maybe even Percy Audio. Rotate through the full range and then reassemble and see if it works well enough without any scratchiness. The pot probably has it's value stamped on it. If it doesn't, you MIGHT be able to measure it and determine the full range resistance value. If this is getting beyond what you would want to tackle, bring it to ANY technician and they will be able to replace the pot for you. The cost should be minimal (certainly under $100).

As for the white spots, try a water dampened cloth first, then try a cloth with a little isopropyl alcohol and then I would just leave it alone because it is purely cosmetic.
HTH
mcfarland
356 posts
 
It looks like they come apart pretty easily. If you do the work yourself, UNPLUG them first! Then try cleaning the volume pots with Radio Shack electronics cleaner, both sides of the rotating pots. Saturate them well as there may be quite a bit of residue that needs to be cleaned, rotate them through their full range of motion. Let them dry, put it back together and see what happens. If they still don't work, see a qualified tech for a more thorough repair. Keep in mind, however, that capacitors STORE electric energy, and can discharge if you short across them (lethal voltages may be present), so, if you don't know what you are doing, PLEASE seek the services of a qualified tech.
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