Casio wk-3800 keys are malfunctioning, also the demo mode pop up abruptly. How to fix

Question moved from Cars and Trucks to a Casio Keyboard one.
Easy enough if you can find the part.

https://www.google.com/search?q=casio+wk-1250+parts+diagram

casio WK1250 Parts and Accessories - PacParts

https://www.pacparts.com > model > model_id=WK1250
Mfg / Model No, Description, PDF, Year. casio WK1250, Musical Instrument: Electronic Keyboard, 1998. The following parts are available for the model listed ...

Casio WK-1250 Repair Parts and Accessories - Syntaur

https://syntaur.com > keyboard > keyboard=2080
Casio WK-1250. Released in 1998. The WK-1250 is a 73-note consumer keyboard with built-in speakers. Synth. All photos are copyrighted by Syntaur, ...

Casio Keyboard Junkyard: Welcome

https://casiokeyboardjunkyard.com Used accessories, parts and stuff for Casio Keyboards ... CASIO WK-1200, WK-1250, WK-1300, WK-1350 models are basically the same and use the same parts.

Casio Repair Parts - Keyboard Kountry

https://www.keyboardkountry.com > keyboard-parts
Casio Repair Parts ; Yamaha Brand Key Lube (Small). $3.80 ; Casio CTK-560L Ma1M Light Boards. $9.95 ; Replacement Keys for Casio CTK-491 and Others. $10.95.
Missing: 1250 ‎' Must include: 1250 ..

From CASIO, duhhh ?

Sounds like either the contacts are dirty or worn out. Solution clean / replace.

It sounds like the sustain is stuck on as if a sustain pedal is active. You don't mention if you have one, however if you MIGHT have one and you have used a Roland pedal, that brand is reverse sensed and would cause note to remain on.

Your adapter should be an AD12M. Some have tried a switching version of this and it has not worked. Make sure yours is the AD12M and not the "ML" suffix one.
The reason is that some of these have filtering built into the adapter, and others do not. The filtering is often required.

Hopefully one of these links can help:http://www.rayburnmusic.com/brook_mays.asp or http://www.rayburnmusic.com/contact.asp or http://mf.custhelp.com/cgi-bin/mf.cfg/php/enduser/std_adp.php?p_faqid=898

One portion of the key scanning matrix has gone bad. First thing is to clean the contacts with 99% isoprophyl alcohol. These USUALLY consist of traces on a circuit board that conductive rubber "pills" under silicone rubber domes are pressed down. Each note usually has two contacts, one closes before the other. This creates "velocity" measurement for the key. IF ONE of the contacts for a key doesn't work, the velocity can detect that the note has actuated, but no release occurs.

This would be on the "STROBE" line for either the first or second contact for THE OCTAVE you have problem with. There are disconnect diodes that prevent sneak paths.

You could have one bad diode, a crack in the circuit board, or a bad connection to the keyswitch board.

Most of these have VELOCITY sensing and that involves two contacts per note. If the velocity sense on those notes is somehow not working, broken wire or trace on the board or short that MIGHT cause your problem.

Have you tried signing on to your computer as the administrator? I looked at the support pages at Casio and saw how confusing they are. Look at page: http://support.casio.com/information.php?rgn=5&cid=008&pid=114 and page: http://support.casio.com/information.php?rgn=5&cid=009&pid=115. Pay attention to the red lettering. The computer might be considered as the midi out device and the keyboard as the midi in device or the other way around, I'm not sure. Pretend its a telephone conversation with one person talking and the other person replying. I don't know if this helps but you can also try tech support at Sweetwater Sound (800)222-4700.

No.

I have a Wk-8000 & a CDP-200R, the later is the same as wk-500 but with 88 weighted hammer keys.

Since wk-500 can play SMF (Midi 0 & 1) format directly from a SD card and there is enough polyphony to play anything, I don't find any real reason to convert SMF to any "Casio Format". Just get a 2GB SD card and put your SMF files in the MUSDAT folder for the SD CARD using your PC/MAC.