Is it only a single note out of tune?
You can try resetting the transpose to shock it back, but if
the detune is consistant with each transposition, then it sounds like a controlling circuit board is out of whack.
Some older keyboards have individual boards or single chips for each note (notice I didn't say "key"). That chip doubles (or halves) it's frequency for each octave.
If the chip that controls the virtual oscilator for a given note is having a detuning problem, it could be caused by environmental conditions (powering up in extremem temps before the keyboard has a chance to aclimate can cause this).
It is possible that the problem will fix itself (unplug the keyboard, remove any batteries and turn it on. This may clear it up).
Much older keyboards have a pot on each note's circuit board that control it's tuning. I doubt that the CZ uses that tired technology (it's an 80's keyboard, yes?).
However, if it does, you'll find that each circuit board has the name of the note lithographed onto it (C, C#, D, D# etc.).
You'll see a tiny silver box or cylinder with a plastic pot inside of it. It'll look like the top of a flat head or philips screw.
You'll need a plastic tweaker to tune the board. Using a good guitar tuner, hook it up to the keyboard (audio output from board to audio input of tuner) and making sure you are clear from any electronics, turn the keyboard on.
Ground yourself, hit the offending note (and sustain it with a foot pedal). Now carefully tune the card while looking at the guitar tuner. Clockwise will sharpen and couter will flatten the note.
Hope this helps you.
Carl
