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Korg Prophecy aftertouch repair?

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Joined: 10 Oct 2011
Posts: 30

PostPosted: Wed Sep 05, 2012 12:49 am    Post subject: Korg Prophecy aftertouch repair? Reply with quote

Hi does anyone have information on repairing aftertouch on a Prophecy?
A few keys on the lower end of the keyboard require much more pressure
to activate than others. The highest key C aftertouch doesn't work at all!
I recall seeing a guide online years ago to repair the aftertouch strip
but can't find it anymore Sad Any assistance greatly appreciated
Thanks Surprised
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Location: Uppsala, Sweden

PostPosted: Wed Sep 05, 2012 8:52 pm    Post subject: Reply with quote

i remember saving some instructions I dug them up, maybe they could be any use for you.. "You must disassembly the Prophecy keyboards assembly and carefully remove the after-touch pressure strip and make repairs. By adding a second layer of rubber to the strip, thereby increasing it's over all height (approx. 1/8 inch thickness) the strip can then make good mechanical contact with each key.
The keyboard assembly holds all the plastic keys, springs, key contact switches and, after-touch strip, all located on a convenient metal base assembly. To remove the entire keyboard mechanism, take the synthesizer and place it upside down and, then remove all screws holding the metal cover plate in place. Next, lift up the silver plastic sheets that cover (held in place using adhesive tape) to expose a circuit board assembly (has two rows of rubber contact switches). Then, carefully disconnect the two wire harness connectors that interface to the circuit board, make a note of their exact position so you know how to put things back together. Now remove the rest of the screws holding the keyboard mechanism assembly in place, it should then drop out from the under side of the synthesizer's plastic housing.
Once you have removed the keyboard mechanism from the synthesizer, the most difficult task will be to remove each and every plastic key (white and black) from the keyboard so the after-touch strip can be exposed and worked on. If you are not careful at removing the plastic keys, they can easily be broken and you will have to order replacement keys. Take all the springs off the keys before trying to remove a key. There is a small plastic tab inside each key, which holds it in place; it is accessed from the top of the key. Inserting a tool to move apart the tap from its normal locking position will remove a key but, it must not be forced or the tab will break-off. One way to avoid damage to a key is to make a tool that just fits into the small square hole on top of the key so it only moves the plastic tab enough to remove a key without straining the locking tab.
(I used an old plastic tooth-brush handle and filed the plastic end so it just fit into the hole on top of a key and this procedure would move the tab aside, I would push this tool into the square hole and then lift up on the key).
You should now be ready to remove and inspect the after-touch strip. You will see two small plastic hold-downs located on each end of the rubber strip, remove these. The entire after-touch strip is held in place by an adhesive glue so, it can be easily removed at this point by pulling up on it from one end and steadily pulling up until it comes off of it's base. Now inspect the plastic and rubber strip for 'breaks' or, 'cracking'. If you see damage, a new after-touch strip will have to be ordered from a Korg Parts Dealer. Keep the old strip assembly because, you can use the rubber strip from the old assembly to improve the design of the new one, (recall I said that an extra layer of rubber would help the keys contact the strip more reliability).
So, you have two options: to order a new after-touch strip or, repair the original one, if it appears to be in good condition. But, what I discovered in doing the repairs is that most problems with the strip are its thickness. The after-touch strip can be improved by making the strip about 1/8 inch thicker. In my case, I bought a new after-touch assembly for $29 and then, before I glued it down on the keyboard mechanism, I removed the rubber strip off the old one and glued it onto the new strip. I placed the extra rubber strip on the opposite side of the other rubber strip so the conductive plastic part was, now, sandwiched in between the two rubber pieces. If you don't order a new after-touch assembly, make your repair by adding an extra piece of rubber strip yourself. Try to locate a rubber much like the one already used on the original and then, cut it to length and width and, then glue it in place as describe above).
Before replacing the modified after-touch strip, you will have to clean the old glue from the base of the keyboard mechanism and rough up the plastic surfaces using light sandpaper so a fresh application of glue can take hold. I recommend using the following rubber contact cement: ("Lapage" Pres-Tite Green contact cement). You will have to coat both surfaces and let dry; putting a second coat of cement on the rubber strip will help ensure a good bond to the plastic part on the keyboard base. Once the two surface are dry, it's time to re-install the after-touch strip onto the keyboard; be careful to make sure there are no bumps or wriggles in the strip when you have finished or, these could effect the feel of the keys and the after-touch response. The repair of the after-touch strip in done.
To complete the work, begin to re-build the keyboard mechanism by replacing the various parts that you removed. I will assume, since you were able to take apart the synthesizer you will be able to put it back together without too much trouble. One word about replacing the keys back onto the metal base assembly, the blacks keys must be put on first and then the white keys, followed by replacing the springs, and then replace the circuit board which holds the two rows of rubber contact switches. Don't forget to connect the two wire harness connectors to the circuit board.

After you have done all the work above, you will be pleased to find how better the after-touch feels and responds to pressure. Not only this, but with the overall downward key travel having been reduced, because of the extra rubber layer you added to the after-touch strip assembly, you may now enjoy overall improved finger playing of the keyboard. I had another Prophecy player test the repaired keyboard and he reported how much better he preferred the author's improvements to his Prophecy keyboard. "
We either make ourselves miserable, or we make ourselves happy. The amount of work is the same.
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Joined: 10 Oct 2011
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PostPosted: Fri Sep 07, 2012 1:47 pm    Post subject: Reply with quote

hi jimmyss75 thank you for posting the information! Appreciate it

jimmyss75 wrote:
In my case, I bought a new after-touch assembly for $29

Look like that's what I need to fix the aftertouch Sad
I wonder if Korg still has the part available.
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