Vintage JVC Amp volume replacement - Page 1
Forum section: electronics / repair

author: mission
author_rank: Contributor
timestamp: February 13, 2017, 06:42:50 am
content: Hello everyoneI have been trying to get the volume (slide potentiometer) to work but it is just too run down to work properly. I wanted to replace it with a new part but I have found it very difficult to find the part, let alone someone who is willing to ship it internationally.Now, I have been trying to make heads and tails of the documentation for the schematic and parts. Since the fitting for the pot is not standard, nor are similar available for purchase in 1 unit I want to swap it out for anything else that will fit and work appropriately.After some time of testing (out of circuit) I have been getting odd results but my conclusion is that the pot is 200k. I can't find anything that will fit in my 65mm space (can possibly fit up to 72mm with some chopping of the pcb which is in the way by about 2-3 mm)Can anyone have a look at the service manual (as some clues may be present there) and the schematic for the volume connection and let me know if 200k pot is correct and if using a 500k with an additional 500k resistor to halve the pot value would make it work (and where exactly would i use it to get the desired effect? across the pins 1?)I'm just a bit confused as to what I can substitute the original for to make it work as nothing out there on mouser and digikey fits my requirements of dual gang 45mm travel 20mm handle(tapered 5-3mm) requirementThanks!https://hawes.co.nz/specialist/JVC_RK-11-L_service_manual.pdfhttps://hawes.co.nz/specialist/JVC_RK-11-L_schematic-2.pdfI highlighted it in yellow

author: edpalmer42
author_rank: Super Contributor
timestamp: February 13, 2017, 07:45:53 am
content: Have you tried Best Buy? It's rather pricey, but it's the original part. If they can get it.https://bestbuy.partsearch.com/Part/Matsushita/JVC/RK11/Matsushita/JVC/QVZ5010008/New.aspxHere's another supplier - also out of stock, but orderable:http://www.pacparts.com/part.cfm?part_no=QVZ5010%2D008&mfg=JVCAccording to the schematic, the value is 250K, not 200K. I don't know why that's not listed in the service manual. I don't know if this pot would be audio taper or linear. You should be able to tell by measuring the existing one. Audio taper would make substitution even more complicated.

author: mission
author_rank: Contributor
timestamp: February 14, 2017, 02:09:59 am
content: Hi, thanks for the input. I already tried the parts place but they do not ship internationally, i even asked via email just to be sureI will try the other link of yours however and hope I get better luck

author: edpalmer42
author_rank: Super Contributor
timestamp: February 14, 2017, 03:25:33 am
content: Are you really sure that the original pot can't be cleaned up? Contact cleaner can't handle it?Could you disassemble it (carefully! Watch for small flying springs or contacts!) and give it a good visual inspection? That might give you some repair ideas. For example, it would give you better access to the resistive elements for a little more aggressive cleaning.

author: BradC
author_rank: Super Contributor
timestamp: February 14, 2017, 03:33:39 am
content: Quote from: edpalmer42 on February 14, 2017, 03:25:33 amI've had *great* results with Caig Labs Faderlube. Wash the pot out with contact cleaner. Do *not* move the wiper until it is thorouhgly dry. Move the wiper, apply, lather, rinse and repeat. Then apply some faderlube and slowly/careful work it around.Moving the wiper with the track wet with cleaner is an almost certain way to damage it. Expensive lesson.Of course if it is too far gone then yeah, replace. I replace if practical, but if I'm up the creek then I'll clean and/or rebuild. It's amazing what you can bodge together once you've cut a pot open so you can interchange parts.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: February 14, 2017, 03:40:19 am
content: If you get desperate enough, I can order it for you and ship. By the time they charge me for local shipping and then I add the cost to ship on to you it will be around $50 US. And that assumes that they really can get the part.

author: mission
author_rank: Contributor
timestamp: February 16, 2017, 06:58:35 pm
content: I have cleaned it up, it works perfect when in hand, due to a long handle that has an extension to use it, general wear and tear are increasing the angle when on it to a point that it keeps getting stuck when in use. This is really irritating.My first option was to clean it up. It's very simple construction. I just think there is too much movement for it to glide smoothly. I can give it another go at adjusting the housing but so far I didn't have much luck once it's back in the amp.Hmm..

author: edpalmer42
author_rank: Super Contributor
timestamp: February 16, 2017, 07:07:47 pm
content: Could you post a few pictures that show the problem? Otherwise, I don't think there's much more we could suggest.