Casiotone - help with repair

[83GLT]

I recently found a Casiotone 401 at a local flea market and have come here asking for help with its repair. Everything works properly except for the sound presets. Only two of them, piano and clarinet, work every time those presets are selected. Of the remaining sounds, the organ works when the unit is first turned on - which is the default - but as soon as i select another sound i can't get the organ to work again. Pressing any of the other sound preset buttons will cause either the piano or clarinet to light up, depending on which row the non_functioning button is located. I can get a third sound, which i think is trumpet, but can't confirm because no led lights up. Finally, if i keep pressing buttons randomly in different order, i can sometimes get a few of the other sounds to light up and play, but it is intermitent and ranfom - for example i can sometimes get the electric piano to play by pressing violin, etc.

I tried cleaning the obs switches for the presets and nothing changed. I think it's a problem with the circuitry. I have the service manual on order and was wondering if anyone here recognized these symptoms or had any similar experiences with this family of casio keyboards and could point me in the right direction.

For what i paid i don't have a lot to lose in opening it up and working on it myself. I have repaired guitar amps and such and have some electronics repair experience etc. But this is my first keyboard and i'm not prepared to pay a professional repair shop a few hundred bucks to hopefully fix it, which is well beyond what the thing is worth to begin with.

I hope someone has some ideas or may have had a similar experiende and knows what to look at. I will also say that i couldn't see any issue with the traces or doldering on the board where the switches are located. I'm wondering if it isn't the main sound chip, the switches themselves or some other such component?

Thanks in advance for any help.

 

[SeaGtGruff]

You said you've got the service manual on order, but if you're talking about the CTK-401 then you can download a PDF version of it from ElektroTanya for free:

http://elektrotanya.com/?q=showresult&what=casio 401&kategoria=&kat2=all

When you go to the page with the manual, watch the third line of text below the image of the cover, which says "This file is downloadable free of charge: ...processing..." Wait a little bit (perhaps half a minute or so) and it will eventually change to say "This file is downloadable free of charge: Get Manual" which is the link you must click on to download the manual.

I'm no good with repairs, but hopefully the manual will help.

EDIT: Never mind, I don't think that's the correct manual, but it was the only one that came up when I searched that site for "casio 401." Still, you might want to bookmark the ElektroTanya site in case you ever want to check it for some other repair manual in the future!

 

[83GLT]

Thanks for your reply. Yes, it's the model CT-401 I'm talking about here. In a nutshell the voice selection buttons do not all work - only piano and clarinet work every time I press those buttons. All of the other buttons either don't work at all, or only intermittently and random. Sometimes if I press the violin for example, I can get the electric piano or trumpet to work. But those results are not consistent.

Just wondering if this is a common problem or one that someone has experience with and can direct me on what to look at for a fix. I'm guessing it would be the component that controls all of the voices?

 

[happyrat1]

Gary

 

[83GLT]

Thanks for the suggestion. Do you suggest this from experience? I don't think the buttons on the 401 are the same though. I will try to take some photos when I open up the keyboard again. I initially though it may be the buttons themselves, but I would need to individually desolder and remove them to open them up and investigate. And given that some voices will engage/light up randomly when I'm pressing other voice buttons makes me think it's a problem in the circuit and not a mechanical problem with the buttons themselves. But I'm a novice here!

 

[happyrat1]

99% sure the problem is worn switches.

Depends what type of switches they are.

If they're rubber membrane or snap dome switches the video I posted would work.

If they're metal snap dome phosphor bronze then they have to be desoldered and replaced.

Otherwise it's 99% unlikely the problem is electrical at the component level since it still lights up and produces sounds.

Either these suckers die completely or else it's just worn or dirty or stuck buttons.

That's the typical point of failure on old keyboards. Worn out buttons.

Gary

 

[happyrat1]

BTW, easy way to check for bad buttons is to use a DVOM.

Gary

 

[83GLT]

^ Brilliant! That's why I'm a novice! I tested for continuity on the switches when depressed and they all appear to be good. I took a moment to peer at the circuit board beneath the keys and noticed that at least one chip appears to be a little burnt and the pins are askew. I will have to disassemble the keyboard further to investigate. I'll report back when I know more. Thanks again for your help thus far!

 

[happyrat1]

Burnt chips with dislocated pins are a definite red flag.

Hopefully you can pull a chip number and replace the culprit.

Gary

 

[83GLT]

Finally got it opened up and i was mistaken. There is no burnt chip and no apparent evidence of any failed components. I have the service manual but this is my first foray into digital electronics repair and i'm finding it a challenge to identify what could be wrong in the circuit.

The only two consistent and working voices are piano and clarinet, and they happen to share a signal path. The other voices are gouped into clusters and none of them work. If it's the main voice chip, then i might not even bother with this unit. New chips are not available, and the cost of a parts keyboard with this chip is going to be more than this keyboard is worth, as will any repair bill be if i take it to a tech. Fortunately, the piano voice is the best of the lot on this keyboard, so at least there's that. But it would be nice to have it fully functional.

Anyone have any experience with this problem on these old casio boards? It would seem that someone somewhere must have experienced this issue? Anyone a casio expert or know where i could find one?

Many thanks!