A K1000 with 5 dead keys *.

There's the power supply on the right, what looks like the keyboard logic decoder board in the middle, and what I assumed was the guts of the Kurzweil sound on the left motherboard, with the four items on the top, from the left: the two control wheels, the volume slider, the data slider, and the display circuitry. All this seemed ok - just dirty. I sprayed and wiped and cleaned it best I could.

Since most of the keys worked, I suspected the problem was somewhere underneath the keypad. How complex would it turn out to be? Let's see...

I took the keyboard out and turned it upside down, at right angles to the case. Hmmm. More dirt. I cleaned it as carefully as I could, with alcohol and Q-Tips.

I unscrewed the two left hand circuit boards and folded them up along their joints:

Immediately visible was a jumper someone had installed previously. Hmmm. So there was a history of a bad connection here. If I was more confident and knowledgable the solution was here, staring me in the face. But I missed it this time. The complexity of the circuit board traces boggled me. If I'd paid any more than $50 for this thing I'd have been chicken to mess with it - but I figured I had little to lose by trying.

I did notice that one of the keys had a plastic lip broken where a metal tab engages it, giving the small metal plate connected to the return spring something to hold to. I managed to shoot that spring across the room several times, even going so far as to buy some replacements in case I couldn't find it. A tiny spring in a crowded room is hard to find, but each time Bonnie managed to find it. I filed a new lip in the key, and it seems to be working OK.

I turned my attention to the keypads. I took off the rubber contact things, and cleaned the circuit board contacts underneath. Also cleaned the contact rings attached to the rubber things. These looked very familiar. I think the CZX-3 has them. I know I've fooled with these things before.

While messing around here, I noticed that I could trigger notes by touching a rubber mounted ring to a circuit contact, unless it was one of the keys that didn't work. However, while the keyboard was upside down, with the black keys being depressed by the weight of the assembly, an Eb which was dead began triggering. Bad Connection, it was screaming! Again, here was the answer shouting at me, but instead I stared back at it for quite a while, trying to grok the logic of the circuitry. Those little traces still boggled my brain.

I put it back together, on the off chance that cleaning had helped some of the keys. Instead, more of them didn't work!

Disassemble, and look closely. Hmmm. The little rubber thingies insert into holes in the metal support structure, which is where the keys themselves encounter them, pressing them down so their little round contacts touch the matching contacts on the circuit board. And these rubber things are very flexible, and it's easy for them to not quite clear the holes when you're replacing the boards:

Also, one end of the string of rubber contacts doesn't have a connecting tab, so it hangs loose:

Have to be careful to get that one in the proper hole, too! Rubber thing not in hole correctly = no note!

So I took the circuit board things off, checked very carefully to replace them with the rubber things in the right places, and then put it all back together. Hmm. The NEW bad notes were gone, but the old ones remained. Ok.

At this point I felt the need for help. I joined the Musicplayer.com Keyboard forum, and posted a help notice. Someone there referred me to the Kurzweil K1000 forum on Yahoo, and I joined that as well. I had to leave it alone then for awhile.

When next I had time to fiddle around, I brought my ancient Radio Shack Micronta voltage/resistance meter to check the contacts. Underneath the keypad circuit board were diodes, two for each note. I checked these, and they all seemed ok. However, I noticed that if I checked the continuity between any of the diodes and one the jumpers nearby it would trigger a note! Cool! Now I'd have a signal to trace.

About this time I got a message on one of the forums asking "which keys are bad?" and of course, just listing them, finding some order to them would be an important step in finding out why they were bad. The fact that they were all in the lower half of the keyboard, and in fact all on the leftmost of three circuit boards under the keypad, pointed to a possible bad connection between boards. I investigated the jumper array.

Now, here there are two plugs, concentric, so to speak, with the outside one being bigger. The contacts on that one are labeled S1, F1, ...F4, S4. The smaller one is labeled 0, 1,...7, 8. Ah, that seemed so much easier to keep track of! Also, that one had direct connections to the diodes that were associated with the notes that didn't work. So I started with that one.

There's a connector that communicates the signals from the keypad to what I assumed was the keyboard decoder board. I figured that, once I figured out the pin layout I could check the continuity of the whole keypad by checking to see if there was a break between any point on it and this connector. So that was my next goal.

Radio Shack continuity testor to the rescue! Here's how it comes out:

Now it was just a matter of checking each diode pair and then numbering the associated notes, 0 ->7, which I did, upside down, on the note ends.

Oddly enough, when I also numbered the diode pairs, the last pair was, I think, a number 3, but the top note, a high G, was a number 4. This couldn't be right! I told Bonnie about this, and she immediately said, "Well, all you've done is number the white notes!" Of course! The black keys were hidden, supporting the keypad upside down. Sheepishly, I agreed. This would not be the last time I did something stupid... !

So I got some alcohol and cleaned the numbers off the key ends and then renumbered them, remembering to skip a number for each of the black keys. Now the pattern was apparent - all the bad keys were 3s! And all on the first (furtherest from the big connector) circuit board. My first thought -- look at those concentric group jumpers again..

I looked underneath those connectors, and, sure enough, there was a crappy solder joint - and it was the fourth one down. That would be the number 3 trace.

I got out the soldering iron and touched up that solder joint. In the little time I had left that day, I checked the keys, and they seemed to work. All should be right, right?

Wrong! The next day I put it all back together and tried it out -- and the same 5 keys were dead! What? Maybe I was mistaken the day before when it seemed to work? Time to tear things apart again.

This time I looked closely at that group jumper. Hmmm. What had I missed? Well, as I turned the board over several times, checking the numbers, I realized that I had been counting from the wrong end -- what I thought was the number 3 trace was actually the number 4 trace! So my soldering, though though it probably hadn't hurt, couldn't possibly have fixed the wrong notes. The problem was a bad connection, right? Maybe just my jiggling and screwing around with things had changed conditions enough so that the notes worked briefly, enough for me to think I'd fixed it. Whatever the facts, they didn't work now.

So my attention went back to that jumper that I'd seen the first day, soldered onto the middle circuit board:

Hmmm. Looking down past the jumper there was a spot of corrosion I'd missed before. Looked like someone had spilled beer or something, years ago, which had slowly eaten into the circuit board:

How had I missed this? You can even see the mark I made next to the diode pair which corresponded to a bad key! I checked the traces, between boards and between the diodes and the off-keypad connector. Hmmm. None of them seemed disconnected...

To check the continuity, I'd been using my ohm/volt meter with the minimum ohm setting - and now that I thought about it, the resistance seemed pretty consistent from one numbered diode pair to another - about 3 to 4 ohms. I decided to check ALL the diode pairs, with their similarly numbered neighbors as well as with the output pins on the big connector --check all the 1s, all the 2s, etc. Ah HAH! All the readings were in the 3 to 4 ohm range, EXCEPT for the diodes corresponding to the bad keys!! Those were in the 12 to 13 ohm range- and just so happened to come through those corroded traces. So, all I had to do was solder another jumper to jump over the corroded traces.

Get out the soldering iron again! As long as I was at it, there was another trace right next to the 3 trace that was bad looking. It's reading was OK, but why not make a pre-emptive strike and jump that one as well? So I put another jumper from a pair of 4 diodes across the bad patch, to the next pair of number 4s. This was tricky, since both jumpers started and ended at neighboring diode pairs, and I didn't want to screw anything up. I carefully put masks of duct tape over contacts I didn't want to disturb, changing them around as I soldered one wire and then the other. Whew! That might do it, I thought.

Wrong! When I put things back together (not entirely - I was getting good at just putting the keypad together and setting it inside the case without screwing anything else down) I was overjoyed to find that all the keys worked - more or less. Sometimes more - all the 4s and 3s were now tied together! Playing any 3 sounded both that three and the neighboring 4, and vice versa. An interesting effect, but not what I had in mind...

Back under the keypad. Looking closely, I saw that as I'd soldered one of the jumpers, being careful not to get any solder bridges between contacts, I'd missed seeing that the insulation had melted enough for a wire to penetrate from below, shorting it to the next diode pair - just what I'd been trying to prevent. A little repair work and it was OK. 

This Story is from another member with permission of course.