problem board on a sp4-7

[tjh]

hello my friends, i have been attempting to repair an sp4-7 given to me by a friend of mine. when he gave it to me it had hardware problems and software problems. i have fixed the software problems by updating the firmware, but the hardware problems remain. i would be very grateful if anyone could offer any insight.

a few keys on the treble side of the keyboard have stopped working. i had thought the ribbon cable would have been the problem, but i replaced it and the same issue kept going. I also tried to plug the bass side into the treble socket on the board and the same keys would not work. the problem it seems is not the keys, but something internally like the circuit board itself or possibly another loose connection. i am not familiar with how these keyboards are made and how they work - does anyone know which board will need replacement, or if there is something i missed regarding the internals?

thank you,
tj

 

[happyrat1]

Each key uses two rubber membrane switches to sense the initial keypress and the terminal velocity at the end of the keystroke.

It's the same system regardless of whether it's a $200 Casio or a $5000 Kronos.

If you do a youtube search on "kurzweil Keyboard Repair" you will find dozens of detailed videos on how to solve this problem.

Sometimes it's as simple as cleaning the key contacts while others it requires replacement or repair of the contact strips themselves.

Good luck with your repair.

Let us know how you make out.

Gary

 

[tjh]

Each key uses two rubber membrane switches to sense the initial keypress and the terminal velocity at the end of the keystroke.

It's the same system regardless of whether it's a $200 Casio or a $5000 Kronos.

If you do a youtube search on "kurzweil Keyboard Repair" you will find dozens of detailed videos on how to solve this problem.

Sometimes it's as simple as cleaning the key contacts while others it requires replacement or repair of the contact strips themselves.

Good luck with your repair.

Let us know how you make out.

Gary

it's not the contacts, switching the wiring so that the left side of the keyboard triggers the treble keys results in the same pitches not triggering even when played on different physical keys. the switches and contact boards themselves are fine, it seems that the problem resides in the electronics after the notes are triggered. i am also seeing that the specific pitches are not passing midi information either.

thanks

 

[happyrat1]

Do you have a 100MHz or better scope or scopemeter?

I'd suggest trying to trace back the signal to the source of the problem.

If it's a logic problem it might be a simple buffer or inverter chip that's quit on you.

Are the missing notes contiguous?

Gary

 

[tjh]

Do you have a 100MHz or better scope or scopemeter?

I'd suggest trying to trace back the signal to the source of the problem.

If it's a logic problem it might be a simple buffer or inverter chip that's quit on you.

Are the missing notes contiguous?

Gary

i don't have a scope but may be able to borrow one from someone. the missing notes are spread fairly evenly across the treble side of the keyboard. i will try to get ahold of one and will see if i can't find the issue. thanks for your help