One Key at Full Velocity. Help!

[MuzikTeechur]

On my main stage piano, Kurzweil SP-88x, I have one key, the C two octaves above middle C, which seems to only play at full velocity on sounds which are velocity sensitive - pianos, horns, EP, Clav, etc. On non-velocity sensitive sounds (organ) it's the same as all other keys.

 

It's sending the same signal out to MIDI as well - when I play my Alesis module from the Kurz that C produces a full-velocity strike.

 

Any ideas?

Please and thank you;

 

Lonnie

[MoodyBluesKeys]

Hi, Lonnie:

The keyswitch itself has either gotten a (probably quite small) piece of trash inside it, or the rubber-like material that forms a "cup" holding the dual contacts has been torn. This is a rather common problem on Kurzweil and a lot of other companies that use the same keyswitches (including Korg).

 

Repair generally involves disassembly of the instrument so that the entire keyboard can be removed and gotten to from underneath. All of the keyswitches are located on two circuit boards. Count up or down to the bad switch and make a small mark on the keyswitch board. Casrefully remove the 20 or so small philips-head bolts that hold the board in place so you can reach the underside of it (the keyswitches are operated by the keys, so they are in the middle of everything).

You will find strips of a grey rubberlike material on that side of the circuit board. Very carefully pull up the strip far enough from the closest end to get to the one keyswitch causing the problem.

With a magnifier, look for any trace of damage or any trash. I use a Q-tip dipped in pure alcohol (rubbing alcohol sold here also contains mineral oil - do NOT use that), and gently clean the inside of the keyswitch. There are two black carbon buttons, which make contact with carbonized copper traces on the circuit board - have a look and clean the circuit board side too.

 

Then you have to get the rubber strip back in place. The little tips that stick through the tiny holes in the circuit board can be pressed back through very gently using something like a straightened out paper clip. It should all fit back neatly with no gaps. Then re-assemble in reverse order of disassembly.

 

Worst-case you find a torn strip - then you need to order a replacement strip of 12 contacts. Kurzweil won't ship direct to you - Sweetwater would be a good bet for getting the replacement part - or any other authorized Kurzweil service center.

 

If the above sounds totally beyond to you - might be best to have a good electronic musical tech take care of it. I've had to clean several on my PC2 and especially on the 2661 (whoever owned it before me got a lot of loose crud inside it). I had an SP-88X which I replaced with a PC2X - but never had to open it - I don't think it is a terribly difficult job, but I spent years earning my livelihood as a musical electronic tech.

 

Jim

 

[mate stubb]

Yup. Common problem with bubble style key contacts that get a little dirt or debris in them.

[MuzikTeechur]

Thanks Gents;

I've gone inside several of my boards before - just wasn't sure what might be causing the problem. I'll do a trash-ectomy later and see what I can find.

[Dave Pierce]

Thanks for this! I've been meaning to post the same question about the 2nd-highest Bb on my Nord Electro 2 61. Does anyone know if the Electro uses the same keybed technology as described here? I'm planning to open it up tomorrow to fix a different problem, and it would be nice to have a look at that too.

 

--Dave

[mate stubb]

Yes, these full velocity notes problems are common on Electro, and it's usually dust or dirt in the bubble contacts.

[MuzikTeechur]

I had some time yesterday to take the Kurz apart. Found a little white speck about the size of a pepper grain on one of the two contacts under the bubble contact.

I guess the velocity sensitivity is derived from the time lapse between contact one and contact two. If a piece of dirt prevents one from contact, I guess the electronics would interpret the second contact as instantaneous and, therefore, full speed/velocity.

It's not critical to know HOW it works (but it's interesting), but if this hypothesis is incorrect, I'd love for someone to correct it.

 

At any rate the Kurz was great on the gig last night. Played on the outdoor stage/band shell at Hampton Beach, NH, for the Labor Day crowd. About 700 folks and quite a par-tay.

 

[Dave Pierce]

Hey, this worked! Thanks for detailed instructions, Jim!!!

 

I took apart my Electro and found a tiny blemish on one of the contacts under that key. It looks like something actually scratched the carbon. Looking closely at the rubber bit above that, there's a tiny indent at the matching location there, like there was a piece of debris that which caused the scratch. However, the debris is gone. My theory is that it got knocked out while I was lifting the rubber strip.

 

Because of the scratch, I wasn't really sure if I had affected a repair or not. So, I just made sure everything was as clean as possible, and put it back together very carefully.

 

Plugged it all in for the moment of truth, and -- voila! Works great. The formerly "full blast only" key is now just as dynamically responsive as the rest of the keybed. Very cool.

 

I love the Keyboard Corner.

 

--Dave

 

[Mr. Nightime]

Was this a Fatar keybed? My Korg Sp200 had some water drip in some time back, and since then I have 3 keys in the highest octave that don't sound at all, and one that sounds at 127. I guess I need to try this fix for that as well.

 

[Dave Pierce]

Yes, it was Fatar (or at least the circuit board that I removed from the keybed was marked "Fatar").

 

--Dave

[Brad Kaenel]

Jim, thanks for great instructions. With your insight, I just successfully performed the same repair on my Nord Stage Compact, and fixed the "full volume" problem. Very interesting to finally see and understand how the real guts work.

 

Kudos to the Nord engineers, too, who masterfully designed a board that's easy to disassemble and work on. Just 10 screws to free the top case from the bottom, and 3 easy-to-reach ribbon connectors to free it from the keybed -- no need to remove any knobs. 18 more screws to free the keybed from the bottom case; flip it over, voile, there's your circuit boards with the bubble contacts. Not scary at all if you work slowly.

 

Extra points, too, because I also found the internal voltage selector switch for when I use the NS overseas :>)

 

Thanks, again.

[Mike Warren]

Extra points, too, because I also found the internal voltage selector switch for when I use the NS overseas :>)

 

Be careful with that. It is often the case that the mains fuse(s) need to be changed when the voltage is changed. It's usually the reason the voltage selector is inside and not normally accessible to the user. Most equipment draws approximately twice the current at 120V than at 240V.

 

 

[Brad Kaenel]

Yes, you're right, thanks. I have the specs for the type of fuse I'll have to swap when I change the voltage. But it wasn't something I immediately realized had to be done!

[Jazz+]

I have 8 keys in a row that have gone dead all at once on my Roland FP4. Does a whole strip fail like that sometimes?

[AUSSIEKEYS]

I have an interesting story that coincides with the above

 

nice new keyboard...one day a bug runs along the keys and as I try to swipe him away he scurrys internally behind the keys...I stop playing and let the keyboard sit for a few days hoping to let the little fellow bug out..

 

well upon playing the keyboard one key responds as above...does hit full volume but starts to fall closer to normal...eventually it is just above normal volume but to my ears devastatingly loud...but eventually it has returned to normal

 

I was not prepared to pull this apart as it was still under warranty,, and wasnt entirely sure the bug was the cause..it has now returned to normal after some use, so problem solved at this point,was it the bug...i think so but won't know until a further problem occurs as it is now out of warranty , luckily I do not need to pull it apart...

 

but if you lose a bug in your touch sensitive organ, flush him out or pull it apart ...

 

or your touch sensitive organ will be buggered.....

[MoodyBluesKeys]

Jazz+:

8 keys in a row failing at once is less likely to be a dirty contact problem. Most keyboards use computer type "scanning" of the keyboard and other controls. Because of the binary nature of computers, things tend to be bunched in multiples of the number 2, and eight is quite popular as a "matrix" number. More likely to be either a bad connection in a connector, a broken trace in a circuit board, or an open diode in a diode matrix.

 

Especially after a few years of use, connectors of the type used in consumer or pro grade keyboards do tend to sometimes not make good contact. Unseating and re-seating them often clears that type of problem. Circuit board trace is less likely, but quite possible. I use an ohmmeter to check at each end of the trace, then a high power magnifier to examine inch by inch.

 

Also can be a problem in a logic circuit Integrated Circuit - but that typically calls for pro service. Oftentimes with modern surface mount electronics, the whole board is changed; as the cost of soldering equipment and microscope for such devices is several thousand dollars. This is less likely, but possible as the cause.