Casio CZ/ VZ/ FZ - Pro Series

hi all!

I just had shipped my first CZ synth :), which I boutgh on ebay.
I already feel this could be one of my favorite synths (I own several rolands, korg, moog, sequential circuits,...)

Through headphones it sounds right, but when connected from the output jack to a Mackie mixer, the sound is so low that I need to increase the mixer channel gain to have it sound at levels comparable to other synths (more than 20dB). (of course the CZ volume is set to the max, and that slider works fine).

I have the impression that it just shouldn't be like this, but I'd like to hear a confirmation, before moving on to try to see if this has to be fixed and how.
It sounds fine, it's just so weird the signal level is so low.
I suspect it might be broken, also because the guy who sold it to me had put a piece of tape on the output jack.... (but this guy said twice it was working perfectly...).

Can comment on the output signal level?

Also, does anybody know in more detail what's the expect ouput level (say for a pure sinewave of given frequency and max amplitude and volume), I mean some objective way of quantifying it, so that I can try to measure it (I own a multimeter, and probably goign to buy an oscilloscope soon)?

Thanks ahead of any suggestion!

Best,
Marco