CDP-135 Self Diagnostic Program

[JLPmusic]

Hi everyone! I just received the keyboard that I "won" from a Good Will auction. It "looks" nice on the outside but 9 keys are not working. From the looks of the inside, a fluid apparently was spilled and got onto the circuit boards. There's lots of rust around the circuit board mounting screws. I cleaned the key carbon pads and that fixed all but 4 of the keys. I thought I would perform the Diagnostic Program I found for the CDP-130. Running the two ROM tests does not give me a confirmation chord but just a lower frequency chirp sound, when pressing the B0 key. I was unsuccessful in finding a YouTube video of someone doing the test to hear what the fail sound sounds like.

 

I was hoping someone could tell me what the pass and fail sound sounds like. And if I get the fail sound, is it worth going further to repair the keyboard? Besides cleaning, is there a way to determine if the carbon key pads are still good?

 

Thanks for any assistance!

[Jokeyman123]

Hard to say from this distance-I have this schematic, one of the better I've seen for a Casio. From that description and yours, error sound seems to be described as a single tone vs. a chord, the single tone being the error code. and since it is triggered by a keypress-it is probably detecting an error in the key scanning process which unfortunately could be as simple as one of the key contacts shorting or not having continuity, or as complex as a circuit malfunctioning from the IC's and circuits responsible for scanning the matrix.

 

Since there is so much damage but you have been successful in getting all keys but 4 to work-seems like all the other functions are working? I would look again at your carbon strip in that section. Not too difficult to get a new matching strip of rubber contacts, see if that works.

 

These carbon contacts are terribly sensitive to contamination and since it is only 4 keys and not an entire octave or more-hopefully the scanning matrix is not at fault, this can manifest as all the same notes being dead through the octaves, skipping depending upon the matrix design, used to be 8 at a time not sure with newer keys.

 

The carbon can become non-conductive-lose its conductive properties but still appear intact and clean. I have used white vinegar and plain water with mixed success on these carbon pads and I would try some simple continuity tests with a multimeter-or simple resistance tests-see if the contacts have retained their electrical conductivity. One probe goes on the carbon contact-then hit a trace down the line from that-might have to scrape a little epoxy off a trce to bare the copper in the trace to do that.

 

4 keys together also suggest a possible break in a trace on the IC boards-could be close to these keys-or a trace much further-you would have to do some visual circuit tracing to see if this is the problem, and it might be.  Again, dilute white vinegar with its mild acid will clean electrical contacts without doing any harm-I would keep any other chemical cleaners away from the carbon or copper contacts below. will only make things worse, I speak from experience.

 

Judging from the service manual, I don't think there is an easier way around restoring this-on a positive spin, these older Casio key assemblies are pretty impressive, the CDP's are pretty sturdy, even compared to the newer Casios and other and depending upon your patience and time, I'd give it another go, but that's me!

[JLPmusic]

Thank you Jokeyman, you've given me some really good ideas where to go from here.