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Just acquired a Kawai CA640 digital piano. The demo and metronome play through the speakers and HP jacks but no sound comes from the keyboard. At first i thought it was a programming issue but cycling the power should reset it. I was told to do a "hard reset" but the Kawai tech said turning off the power does the reset. In programmming mode I tried to adjust the metranome volume with the first 7 keys and nothing happened. I suspect the CPU board or keyboard is bad. There is +5v at the 2nd pin on the CPU board going to the keyboard. Is there a way to jump the 2nd pin to another pin on the CPU to see if it is the keyboard or not? If it is the CPU board someone said to try cleaning all the small holes with a fine copper wire? or check for cold solder joints. Kawai tech said C112 cap leaks and causes issues too. Novice with a DMM...

CPU and sound generation must be working. Sound like either

1) failed keyboard controller
2) Not power to above (bad connector?)
3) No data from above (bad connector?)

You might be able to fix #2 and 3 my playing with any cables. Move the conects on and off the PCBabout 100 times and maybe some contact cleaner (comes in a spray can at electronics shops)

If you had not said you were a novice with DMM I'd suggest some circuit tracing but if finding and fixing a loos connection does not work take it to a technician and have him fix it for you. He might apply some logic like "if a key contact switch is open there must be some voltage across the switch that goes to zero when it is closed. if not then whatever makes the voltage is not working or not getting power. If it it's there then the prbolen is between here and CPU,..... That's the kind of reasoning he's use and you can't learn in from a web forum post.

Some techs can only apply this logic to find which PCB (board) needs to be replaced. Others are better and can find the dead 5 cent part, (like maybe that leaking cap.) So you might ask when selecting a tech if he typically does repairs at the component level.

Many times getting a new PCB assembly is not worth the cost.

Chris,I got it at a reduced price because it didn't work any more. I am pretty good at fixing electrical and some electronic equipment. I never saw the circuit board with the little holes going through it before. I found C112 and it was corroded around the cap so I cleaned the area with plastic friendly contact cleaner. I cleaned all the holes with a very fine wire and started tracing the connections. In the process of that I found three of the holes looked different and not shiny gold but more like a copper color. Ran out of time last night. Before I take apart the keyboard I checked the resisters in the circuits that I could through the keyboard connector at the CPU and they checked out. Is there a way to simulate keyboard strokes by jumping out the keyboard pins on the CPU and then I can concentrate on the keyboard circuit under the keys only? I have +5 volts on the #2 pin to grnd.

If you found corrosion around that capicitor, it probably means it is leaking. Is it by any chance bulged or swollen at the top? This indicates the capicitor is either bad or going bad.

Does the keyboard work, when the DP is connected to a MIDI device, e.g.pianoteq?

Not familiar with the model, but have you checked out the manual, for 'Local Control' on/off settings?

just checked the capacitor with the DMM and it seems to be ok. I get high resistance and then it goes to infinity everytime I switch the leads around and it is not bulging. Took all the keys out and traced all the CN1 wire connector wires to points on the keyboard circuit boards. looks like there is continuity on all wires. ugh! I can't see straight anymore.

I checked with the Kawai technician and he said that cycling the power will reset it.

If you don't have MIDI cables handy, you can isolate the keyboard from its role in actuating the tone generator:

Press the 'Rec' button, then see if pressing one of the keys causes the Play/Stop LED to light up:



The keyboard is also used when adjusting settings such as the metronome volume. Instructions can be found in the manual.

If either of those functions fail to work correctly, then the "CPU" is likely not receiving data from the keys.

I tried to set the metranome volume in the programming mode and it involves using the first 7 keys which did not work. If the keyboard is not the problem where can I look for the problem on the CPU?

It sounds like there's some confusion in terminology. By "keyboard", I meant specifically the "bank of 88 white and black keys, and their sensors."

Based on the results of your metronome programming test, the keyboard (and its connection to the rest of the DP) is a good place to focus your troubleshooting.

all 88 keys are out and circuit boards removed. nothing looks obviously bad. Started tracing out circuits through the CPU end of the keyboard connector plug on to the keyboard. continuity through all wires to both circuit boards. with power on and keyboard harness connected get the following voltages to ground on the keyboard circuit board:
pin 1=grnd
pin 2 has 5 volts to grnd
pin 3 has 1.6 volts
pin 4 has 1.6 v
pin 5 has 2.5 volts
pin 6 has 2.5 v
pin 7 has 2.5 v
pins 8 to 15 all have 5 volts to grnd.

I fixed it! one of the small holes that goes from the top of the CPU board to the underneath was corroded under the leaking cap (C-112). had a very high resistance on the connection between U3 and U30 chips. put a small wire in the hole and a drop of solder. keyboard plays now. thanks to all for your help.

Wow, nice job!

Cheers,
James
x

It turns out I have the same model keyboard with similar symptoms. Can I assume that I need to replace that capacitor? How can I make sure that I get the correct capacitor?

Thanks for any and all help!

No you can't just assume it's the same capacitor and problem, but it could be a leaking capacitor and dry or high resistant joint. Start with a visual inspection, then get the multimeter out just like fx did.

Most capacitors that are bad or going bad will show visual indications such as bulging or leaking, but not always.

On the capacitor itself, you have to look at the mF rating (capacitance, measured in microfarads) and the voltage. This will be printed on the component. Then find a matching part. They need not match visually, just the specs (you can even go up on the voltage rating if you can't find one identical, but you can't substitute with a lower rated cap). Be sure to match the stripe on the cap with the markings on the board when soldering it in. It would not be a bad idea to replace every capacitor while you're in there. Capacitors are cheap.

When you're removing the old capacitor, be sure to suck up all the old solder from the previous capacitor. Use a solder sucker first and a solder wick to soak up the excess.

I would have felt better if the OP had gone ahead and replaced that leaking cap when he could, but he has probably had to by now or will soon.

Here's a good video on replacing capacitors. In this example it's an LCD monitor, but it's all the same really.

http://www.youtube.com/watch?v=jdDNW6r2hDg

Thank you for this help! We're teaching music in Kuwait and it isn't easy to find technicians who can work on musical instruments. One more question: It *is* the same capacitor that fx had problems with (C-112) that I am seeing a clear sticky fluid around on the circuit board. Is there some way I can clean up that stuff without ruining the board? And do I need to get it out of the tiny holes too?

One more note... I'm not sure that this (C-112) is really a capacitor. It kind of looks like a small battery to me. Can I email a picture of it to someone to verify?

Put a photo on here. Is there any writing/printing on it? To clean the gunk you need an alcohol based cleaner (available in Kuwait?), or similar (paint thinner, ask in hardware or DIY store), that does not leave a residue when dry.

This sounds like a small repair job that's about to turn into a large repair job.
Honestly, if you don't have the skills to do this, expect to do more harm than good.
Instead, get a technician to do the work.