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Sourcing pots for E-MU Xboard keyboard
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sisbrains



Joined: 14 Feb 2010
Posts: 15

PostPosted: Sun Feb 14, 2010 7:47 pm    Post subject: Sourcing pots for E-MU Xboard keyboard Reply with quote

Hi everybody, I am trying to fix my E-MU Xboard keyboard, the mod wheel pot is jumping from 0 to 127, instead of giving out a gradual transition from 0 to 127, as soon as I move it a little, the display showing the MIDI output jumps from 0 to 127.
One of the knobs on the top of the keyboard, which is used for sending MIDI CC messages, only starts registering movement when it's about a third of the way round, after that it works fine, but I would like to replace it too.

I have taken photos of the two pots, and have been looking all over the internet for somewhere to buy replacements from, but haven't found the exact same pots, plus I don't know the resistance (?) of the square one on the fascia knob, and don't want to unsolder it in case I can't get a replacement anyway, I'd rather wait until I have the replacement before I unsolder it.

Can you help me? Here are photos of them.








I'm a bit confused as to why the mod wheel one says '90' on it - I presume that that means it has a centre point which is 'zero', and then can move either side of that to give out a value. I've checked the pitch bend wheel's pot, and that is exactly the same (which would make sense, because the pitch bend wheel is held in a central position by springs, until you move it either up or down, but the mod wheel starts at the bottom and moves up to the top).

They both have 'flat' shafts - is that the terminology I should be using when searching? I've been searching for "10k flat shaft potentiometer" and variations on that theme.

I presume these are fairly standard pots and nothing specific to E-MU products, but I've spent two hours trawling websites to find a retailer that sells them, and I've come up with nothing, so any help would be greatly appreciated.
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sisbrains



Joined: 14 Feb 2010
Posts: 15

PostPosted: Sun Feb 14, 2010 8:05 pm    Post subject: Reply with quote

Sorry, here are the photos of the mod wheel pot:







(I could only post two photos on the first post, for some reason.)
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jts1957



Joined: 24 Nov 2008
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PostPosted: Mon Feb 15, 2010 2:32 am    Post subject: Reply with quote

Have you tried to "clean" them with a contact cleaner aerosol spray?
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sisbrains



Joined: 14 Feb 2010
Posts: 15

PostPosted: Mon Feb 15, 2010 1:30 pm    Post subject: Reply with quote

Hi jts, I haven't tried that, but I did disassemble the 10k pot (the lower set of two photos) so that I could see the 'track' (sorry, don't know the terminology), as I read that you could use a pencil to recoat the graphite. Anyway, inside it has only one area of graphite, about a third of it, at the top, the two sides were just copper (or some other metal). Is that normal? I suppose that's something to do with it being a '90 degree' pot, the same as on the pitch bend wheel. I'm sure it isn't supposed to be like that.
The tracks looked fine, I can disassemble it again and take some better photos of them, if you think that might help diagnose the problem.
But if you know where I can buy the right pots, that would be a great help.
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sisbrains



Joined: 14 Feb 2010
Posts: 15

PostPosted: Mon Feb 15, 2010 1:43 pm    Post subject: Reply with quote

Do you think the top ones (the rotary knobs which you send MIDI CC messages with) are likely to be encoders, rather than pots, like this:

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=6234293

And do you think this will suffice to replace the mod wheel pot:
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=23E+1+turn+carbon+track+pot%2C10K+lin+20mm&x=39&y=11

I might have to cut the end of the shaft off to make it fit, but otherwise it looks like it might work. I presume they will both be linear, not log.
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jts1957



Joined: 24 Nov 2008
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PostPosted: Mon Feb 15, 2010 10:13 pm    Post subject: Reply with quote

No disassembly required. Just attach plastic extension tube to nozzle, poke other end into any opening in the pot or switch and give a short burst. Rotate/slide control/switch to work in, repeat as necessary.

http://www.radioshack.com/product/index.jsp?productId=2103700#
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sisbrains



Joined: 14 Feb 2010
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PostPosted: Mon Feb 15, 2010 10:58 pm    Post subject: Reply with quote

Thanks JTS, I will try to buy some of that tomorrow and give it a try - a lot easier than replacing the pots - and they have had hardly any use anyway (I think I've turned the mod wheel about 100 times, and the MIDI CC wheel only the once!)
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sisbrains



Joined: 14 Feb 2010
Posts: 15

PostPosted: Mon Feb 15, 2010 11:02 pm    Post subject: Reply with quote

Do you think it's odd that the mod wheel has a 90 degree pot, the same as the pitch bend wheel? That doesn't make sense to me, but I'm not that hot on electronics (obviously!).
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jts1957



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PostPosted: Mon Feb 15, 2010 11:19 pm    Post subject: Reply with quote

Don't ask me. My field is consumer electronics (TVs, computer monitors and stereos for the most part). But parts (pots) is parts (pots). Very Happy
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vtech



Joined: 08 May 2006
Posts: 1264
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PostPosted: Tue Feb 16, 2010 2:35 am    Post subject: Reply with quote

In looking at your first set of pictures, apparently those are in fact rotary encoders which are completely different than standard potentiometers. (the microcontroller Atmega48 (U1) to the right of the controls is a solid proof) While tarnish can still build up inside the controls and cause erattic operation, there is a possibilty that you may have a digital problem? Ofcourse as jts1957 suggested you may want to spray clean it first. Keep in mind that spray-cleaning might cause a somewhat stiffer operation if you happen to have a very smooth-operated potentiometer--so don't spray all of them. As it cleans the contacts, it will also clean out any dampening fluid used for smooth pot operation.

On your second picture, while not an encoder, it looks to be similar in operation to a Joystick potentiometer. Meaning that the full 10k ohms is linear and accomplished within 90 degrees instead of a standard ~ 300 degrees pot.
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