This keyboard has sure kept me busy! In answer to some of the comments here, no, it isn't really a
weighted touch. It's better than most synths, in as much as the keys have little weights glued into them (so
maybe it really is a "weighted" touch?). They don't feel quite as insubstantial as a regular synth, but it doesn't
replicate the feel of real piano action. I've played some keyboards lately that really do well at that- but then,
I didn't like the sound of them as much as this thing.
Not that it's perfect, by any means. I've begun to notice some distortion, some weird overtones, in the
sound, but they don't detract from (and maybe they actually add to) the realism of it. Let me
put it this way- I still get a lot of pleasure out of just sitting down and playing this keyboard after 20 years. I
don't know of any other electronic keyboard I could say that about. Which
is why I keep patching this thing up, rather than buy a new one.
So. The latest problem was a long time coming. Years ago, before the last repair, my B below middle C key
got weak. It would still sound, only it was not as loud as every other key. When I opened it up to fix that nasty crack
I had a look at the mechanism of that key, but couldn't see anything wrong with it, so I left it be. Sometimes I do more
damage just messing around with stuff than it's worth. Well, recently a strange thing happened. I completely lost the
Eb above middle C key, while at the same time that B key fixed itself!
This had to be related, but how? The keys operate like this-
This is a side view of a key. Over there to the right, there are two "triggers" that stick down. These
press down on two rubber "domes" when you press down the key. The inside of the domes have a conductive material
in the top. This gets pressed onto conductive areas on a circuitboard and completes an electronic circuit, which
the Kurzweil then registers as a key press. It's basically a switch, and is like the switches in a cell phone or
TV changer. With one difference...
There are two switches per key. This is how the Kurzweil determines how hard you strike the key. See, it doesn't
literally measure the force you apply. What matters is how fast you hit it. The lightning-quick computer in the keyboard
actually can tell the length of time between when the first switch makes contact and when the second one touches. It
then calculates the speed of (and therefore, force on) the key and adjusts the volume of the note accordingly. Clever.
Now, when the B key got weak, I sort of thought that one of these domes had cracked and wasn't making contact
at the right time- therefore leading the keyboard "brain" to think that a heavy hit was a light hit. But the domes were
both in good shape, and I didn't want to dis-assemble that part of the keyboard at the time. When the Eb key stopped
working completely, I knew I had to get in there. A key that's a little quiet is "character". A key that doesn't work
is "broken".
This is a view of the underside of the key assembly. (I leave it to you to review the previous fixes to
determine how to get to this point) You see the brown circuit boards? On the left the screws holding one on
are still in place- on the right, the screws have been removed. Also, there are those red connectors here and there that
need to be carefully disconnected. (You may notice that I've also removed some keys in this area- that
wasn't really necessary).
Here I've removed all the screws from one section of contact circuit board and flipped it over. On
the lower half of the picture you can see the triggers which stick out under the keys. On the top half you can see
the rubber domes that those triggers press onto. (my drawing wasn't exactly right, but the idea is the same). The domes
in that area look fine from this side- now we gotta go in there!
Now, this a view of the contact board with the rubber domes removed. You can see there on the right a bit
of the rubber piece- it's actually about an octave or more worth of switches in one chunk. Little nubby bits poke through
holes in the circuit board to hold it on. Be careful when removing it- I pushed these through the holes from the far side,
rather than pulling them through, to keep them from tearing off.
You see a black dot inside the domes of the right? That's the conductive stuff that gets pressed down onto the black oval-shapes on the circuit board. It actually contacts two ovals, closing a circuit. If these get dirty, there can
be problems... wait a minute! What's that there?
Oddly enough, right next to the contacts of the non-functional Eb key, there was this little tiny fleck of
something (circled in red). If I didn't know better, I'd say it was a piece of peanut skin, but of course, I would never
shell peanuts near my Kurzweil! Well, maybe... The yellow boxes indicate the areas where the conductive spots on the rubber domes contact the circuit
board. It isn't hard to imagine that if that little bit of dirt was in the wrong spot it would prevent that dome from
making contact- and the key wouldn't work.
How might it get in there? Well, the domes have holes in the sides of them to let air in and out when they
are pressed down. This "pumping" action might have been the reason for the simultaneous "self-healing" of one key and
failure of another- maybe that same little fleck of dirt got blown out of the B key and sucked up into the Eb key! Anyway,
I carefully brushed all these contacts with a camel hair artists brush, then vacuumed out the inside of the keyboard
after I had reassembled the rubber dome piece and contact board. Fixed! It's probably a good idea not to let your
Kurzweil get too dirty.
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