I'm not very familiar with the CT-X700 yet, but it sounds like you might be accessing the Split Point function-- or whatever Casio calls it-- which sets the key where you want the keyboard to be split. I believe Casio identifies Middle C as C4, in which case F#3 would be the F# below Middle C. I think the two left-hand voices are called the Lower 1 Tone and the Lower 2 Tone. I'll look at the user's guide later to see what it says.
First of all, I was wrong about "Lower 1" and "Lower 2." The CT-X700 and CT-X800 have only one "Lower" voice. (The CT-X3000 and CT-X5000 do have "Lower 1" and "Lower 2" voices, which confused me.)
I see that the SPLIT button is used both for toggling the split mode on or off and for setting the split point. If you hold down the SPLIT button, the split point is displayed, so it might be that either (1) you're holding the SPLIT button down too long when pressing it, or (2) there is some sort of problem with the SPLIT button or its circuitry.
When you press the SPLIT button to toggle the split mode on or off, an "L" is supposed to appear or disappear on the LCD screen. Can you make the "L" turn on and off by tapping the SPLIT button? If you can, then hopefully there is no problem with the button or its circuitry. But if you cannot, then you might want to contact the store that you bought the CT-X700 from to see about returning it for replacement or repair.
If you're able to toggle the split mode on or off successfully, I would try turning it off, then following the procedure for selecting the Lower voice exactly as described in the User's Guide:
(1) Tap the TONE button to enter tone-selection mode, then select the tone you want to use for the Upper 1 voice.
(2) Tap the SPLIT button to toggle the split mode on, then select the tone you want to use for the Lower voice.
You're welcome! I'm glad I was able to help you. My Yamaha keyboards also have buttons that serve two functions-- one by tapping it and the other by pressing and holding it-- so I know how tricky they can be.
SeaGtGruff, this place would fall apart without you. Thanks for the info.
My sister just purchased a Casio WK-6600. Totally out of the blue - I had no idea she was even contemplating a keyboard purchase. On my end, I've now got my Kurzweil and Yamaha set up and playing. My next kbd will be the 76 key version of the CT-X5000, assuming they choose to make such a beast. Hoping for a January announcement...