mygrove

Thanks for that. I am guessing you meant FI4 and SI4 as this is the block I'm having problems with? These are the pads each end of the ribbon cable on the keyboard pcb and main pcb?

Thanks again @Jokeyman123 I'll try some magnification over the solder at the weekend. I'm sort of OK understanding the schematics but I find the challenge interpreting this on the actual board. Perhaps one point you could clarify for me is how the signal from the keys being depressed is combined and then passed over the ribbon cable. As I know that the silent keys precisely align with the F14 and S14 rows from the Key Matrix, it seems a component or joint that is common to them that is at fault. I also wondered whether the faint sound that is heard when first switched on and depressing one of those keys is a symptom of a failed capacitor. Thoughts?

Thanks @Jokeyman123. You prompted me to study the Service Manual a little more closely. I have annotated the relevant areas, but when it gets to the logic and circuit I'd need some help. If you think there should be any more useful pages I'll attach those too. I can't see how you attach files here so here is an external link to the pdfs Casio CTK-611 pdfs

I have acquired an (old) Casio CTK-611. All seems to work as expected, except that 8 keys in the centre of the keyboard do not work. The keys are G#4, A#4, C#5, D#5 and A4, B4, C5, D5. In fact, when you first switch on they can be used once but only sound very faintly, then nothing. I have had a look under the keys to see if it was perhaps a dust issue - it wasn't. Looking inside it is the first 8 notes of the second half of the keyboard on pcb KY2M. I understand this board was a common component of many Casio products. I get the same nil response by pressing the pair of rubber pads at the sametime. But is it this pcb that is likely to be the problem or something else? Any clues on fault finding are appreciated. (I have posted a similar question elsewhere but it has been suggested there may be more folk with knowledge of fixing Casio keyboards here - let's hope so!) Thanks.