Roland VS-840 sliding pot replacement

[dkevin]

I realize this might be a silly question...but...how can a 10K work in an application that specifies a 50K pot? What lack of function may result from such a substitution?

[Enzo]

NO lack of function. As was explained, the sliders are there to vary a control voltage. They are all wired across the +5 supply, and the wiper makes a control voltage that varies from 0 to +5v. Doesn't much matter what value the pot is, within reason. Halfway up is half of the voltage, in this case 2.5v.

[dkevin]

Thank you!

[dkevin]

Repair or replace pots?

I have spent a lot of time trying to find these Panasonic sliding pots. Evidently, so have a lot of other people. Meanwhile, I have run across a couple of videos on how to remove, disassemble, clean and lube faders. My first choice would be to replace them if possible. But barring that, I would be willing to take a hack at removing and reconditioning them. If you have an opinion about this course of action please let me know what you suggest. As of now, only one of my track faders is inoperable according to the internal test program built into the Roland VS-840. But if I can successfully remove and repair this one fader, I will probably do them all as a precautionary measure. This unit was pretty dusty and dirty when I received it. Let me know what you think.

http://www.youtube.com/watch?v=V4LIFUzgpjs

http://www.youtube.com/watch?v=LZ2sg1owFyg

[dmeek]

I haven't had much luck re-building these faders. Usually the wiper is corroded. Wipers are interchangable, so if you have a good fader of the wrong size in your
parts collection, you can sometimes steal the wiper if the contacts (stereo or mono) and the shaft are the same.

[dkevin]

Given the parameters of the datasheet, I wonder if the "EWA-Q1----" Panasonic pot has the same wiper as the "EWA-P1----" pot. The P stands for the throw of the pot I think. I can find tons of the Q pots for pennies while the P pots are almost impossible to find. If the wipers are common to these two models, I should buy a handful of them just to have a stock of replacement wipers. I don't know if Syntaur still has their 2 pots in stock, but I am not eager to pay $20 per pot to have their replacement pot.

[g1]

Have a look at the datasheet in post #14. As far as I know P is single and Q is dual. So I'd expect the wiper to be different.

[dkevin]

Post #7 is the ill-fated Bourns pot I thought would work as a replacement. Post #14 is the EWA Panasonic pot data sheet. I was asking about the feasibility of using a EWA-Q1... pot wiper to replace a damaged EWA-P1... pot wiper. Your answer may well be the same but I thought I'd clarify which data sheet I was referencing.

[g1]

Yes, I meant post #14, sorry (edited above).
And I'm mistaken, Q means 60mm, not dual. A is 45mm.
Q1 is single, Q3 is dual.
So if you can find a Q1, the wiper should be the same as the P1.

[dkevin]

I desoldered the non-functional #2 pot and removed it from the board. I took it apart and cleaned it out with alcohol and a swab. Man! what a mess! The sweeper/wiper was clogged with gunk and junk and I had to clean them carefully to avoid bending the contacts. After cleaning I lubed the plastic parts and reassembled the pot and tested it with just a few of the tabs bent to secure the casing. After testing it I bent all the tabs back into place and reinserted the pot to the board and soldered it. Given the debris I found inside the pot I am thinking I should remove and clean all of the pots. I bought some DeOxit pot lube and am using it sparingly on the plastic parts. The pots are sure smoother and prettier. Given the inacessibilty to new replacement sliders, I am buying parts- pots to have a supply of the lever-slider-contacts that seem to be most easily damaged with dirt and gunk in the pot. The part number I am buying is a Panasonic EWA Q12 C10 B14 .... It is not an identical pot to the original P12 C15 B14 but the lever and contact elements are thought to be the same. We shall see...One last thought...If these were designed to be consumer grade devices and subject to a hostile environment (dirt, dust) why in the world wouldn't they use a pot with a shield to protect the sensitive contacts inside the pot? I don't think the cost would have been outrageous.

[dkevin]

Donor pots arrived and I disassembled one for close-up pictures. The lever is metal as opposed to stock plastic but all the remaining pieces appear to be identical to the VS 840's original pots. I will use these donors to rebuild the original unobtainable pots and keep this beast going. https://imgur.com/a/XdcXwSU

[g1]

Can you add link for the ones you ordered?

[dkevin]

The ordered part number is in the picture gallery and also in the later posts. I ran across this interesting website about different methods to restore and rebuild sliding pots..

.https://www.keithrobertmurray.com/ar...-showdown.html

[g1]

I see you mentioned the part # you used as wiper donors in post #25.
Thanks

[dkevin]

I removed all the pots one at a time and disassembled and cleaned the parts. I used alcohol and q-tips to clean out the grit and gunk.I inspected and reassembled them if the wiper fingers seemed to be in good shape. I replaced the sliders on two pots due to excessive wear. I used Deoxit pot lube to build them back up. I tested the pots several times..once with only 2 tabs securing the case to check the resistance and smoothness of operation. I checked them again before soldering them to the board. I double-checked all my solder joints and am ready to begin the re-assembly.

https://imgur.com/a/XdcXwSU

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