CT-6000 in need of repair

[CRABFLAG]

I bought a broken CT-6000 from Craigslist. It was in ROUGH shape. It powers on but there is only a static sound coming from all speakers and outputs. I have opened it up, cleaned the inside and replace one blown resistor. Everything else looks good and I have used a multi meter to check that the main boards have power. It almost sounds like something between the synth and the main output board is not hooked up correctly and it is only sounding some electronic interference.

Any advise is welcomed! Is there a possibility that I could repair this or is she ready for the graveyard? 💀

I have some photos of the boards and a short video of the sound in this google drive folder: https://drive.google.com/drive/folders/1mK-NVLZ-nR4NFnlxD7rVhsK6HQP1wVlg

[pianokeyjoe]

Ok, thankyou for the detailed photos and the sound video example! I was looking and I noticed alot of what looks like dried or semi dried liquid on the component side of BOTH slider control panels. Also first thing that came to mind is "sliders" when looking at the back of said control boards where the wires connect to the sliders. These wires are audio input/output cables. You keyboard is fine, you just need to clean the boards and then resolder the wires. IF that does not work, the next logical step is check your MAIN VOL slider. The best way is to short the pins on the slider at one end or the other and check for audio. Yamaha PSR11 keyboard with similar issue was bad main volume slider due to liquid damaged slider carbon contacts. I needed another slider but instead of waiting to find one I just shorted the MAX volume pins to give me max volume and bypass the slider. Now my keyboard is loud ALL the time. As it should be.  Check your sliders. The sounds you are hearing are normal cpu sounds. How are they normal? Everytime you pressed a key, it made a sound, and when you change a preset it makes that sound but some presets make it louder and brighter and some presets make it duller and muffled. That is the filters in action. If you press the rhythm start and hear a very faint pattern to the noise, then yes, you have a classic DEAD volume situation going on. Another thing to try is slide the main volume and the other sliders one at a time to see if the noise sounds go down in volume or stay the same. IF they go down in volume, then the issue is a cold solder on one of the input/output wires.. Let me know what you find, and consult back.

[CRABFLAG]

@pianokeyjoe I did hear a very faint drum pattern! I will work on cleaning this and get back to you. Do you have a recommendation for a board cleaner?

Edited November 8, 2022 by CRABFLAG

[pianokeyjoe]

For cleaning the boards themselves, i used rubbing alcohol and electronic contact cleaner as well as a mix of baking soda and white vinegar if nothing else works as this neutralizes acids and alkalis like those from batteries and soda spills. I use paper towels and distilled water if nothing else is needed too. The shorting the main volume would be the first thing to do. Once you have determined you have sound, then work on cleaning and changing that slider. The goo on the boards looks like dark soda pop spill so syrup? Good thing for you is it is NOT, I repeat, NOT pee!!! I have a dead Yamaha PSR70 that is pee pee damaged.. so sad..

[CRABFLAG]

@pianokeyjoe   I cleaned the board with rubbing alcohol, removed the wires for the main volume slider and cleaned the contacts with contact cleaned and then resoldered the wires. I added some before and after photos in the google drive folder. I have not put it back together or tested it yet. What is the best way to short the max volume pins to try and give this thing full volume?

 

Thanks for the help so far!

 

https://drive.google.com/drive/folders/1mK-NVLZ-nR4NFnlxD7rVhsK6HQP1wVlg

[Chas]

@CRABFLAG - Good luck with your CT6000, and I hope you can get it back to good health again. They are very unique and very lush sounding keyboards, and they're most definitely worth saving.

 

I can't add much more advice to what @pianokeyjoe has already suggested. Only thing that I could have added would be to hook it up via MIDI to a DAW/ other MIDI keyboard and see if it's sending MIDI correctly. If it is, then that suggests the main CPU and associated controller circuits are functioning correctly. Though as you've already got yours apart to tackle the soldering and volume slider that might not be possible at present. Fingers crossed the soldering and volume slider will sort it all out. Good luck! 

[CRABFLAG]

@Chas when I got it home I hooked it up and was able to use it as a midi controller and when I sent midi into it it was making the weird sounds the built in keys were making. So midi communication works and I’m going to use the midi input to test it so I don’t need to keep putting it all together just to test. Just running midi in and one audio cable out for testing. 

[pianokeyjoe]

@CRABFLAG So you have midi tested it too? Ok. So it IS the volume slider. Ok, turn the unit on, and while pressing some key or press the rhythm start button to have sound going. Now take a wire with both ends stripped and there are 3 solder points for the main volume. plus the slider metal chassis ground. Take the wire and touch one end to one of the slider solder points and short to another point, then the other and hear for the keyboard to spring to life. Flip the test points, if the first shorting test did not do anything. I think on the Casio it is the 2 solder points side by side for max volume but it could be the single solder pin at the one end of the slider shorted to one of the side by side solder pins at the opposite end. Make sure to slide the volume to max on the slider itself just in case, obviously lol! Funny, I had to do this for the rhythm section volume on my unit. I was able to fix it like that and thus that is how I KNOW the beats are similar to the CPS201 which is a heavy analog style beat tones not found in many Casio keyboards outside the CPS201/CT6000 class series.

[CRABFLAG]

@pianokeyjoe sorry for the delayed response. I have tried touching points together on the volume slider to see if anything would work and I can still not get this thing to make noise. I even tried connecting the red, white and black wires connected to the master volume together hoping to bypass the slider. The electric hum went away when I did that but still no sound. I am not sure what I would even do now.

[CRABFLAG]

@pianokeyjoe This keyboard also has a separate melody and rhythm volume sliders. Is there a chance that those are not functional also? Maybe they all need attention? When I connected the wires to bypass the master I was able to hear the rhythm section without the static sound but it was still VERY QUIET. So maybe the volume going into the master is quiet or just not there for the keyboard? Is there another way to test the keyboard sound?

[pianokeyjoe]

I do believe the melody and rhythm sliders may need attention but the odds of all 3 going bad at once is kinda out there but not improbable. I would say on the main volume, put everything back the way it was since you could hear something. Next thing to check is the amplifier section. I am sadly not able to get to my CT6000 parted out keyboard or the good one to guide you through yet. Hopefully some one else can help here? I have only yesterday posted my first youtube video about my own Casio keyboard issues. But as time and remodel progress allows, I should be able to get to my own keyboard(CT6000) eventually and post any findings here. Sadly, not any time soon. If you are not getting amplification in the Speakers nor the headphones, did you try the direct output jack on a guitar or computer speaker? If that does not work either then your issue is Amplifier section related and that will take more time and care to diagnose.

 

I did take a look again at the pictures and noticed the volume slider board is operating as a Stereo system so you have LEFT and RIGHT(white and Red)wires both going IN and OUT. Did you touch the wires while the keyboard was ON to see if there was a hum when you touch the amp wires at the main volume? If you did and the hum was loud or louder as you pressed harder on the wire solder points, then the Amplifier does work and your issue IS the sliders themselves. I know it sounds confusing since you would hear the hum for the amp INPUT wires but in the case of the volume controls it is a backwards thing. because one of those cables is coming from the SYNTH chip section IN to the volume pot, and the other cable is going OUT of the volume pot to the Amplifier. So touching the OUT wires will HUM because that is the Audio INPUT of the Amp section. If you can follow? The sliders all may be toast due to the Soda or juice spill you cleaned up off the board in general. My suggestion, is find out if you have audio on the amplifier first. IF you DO, then what you would do to bypass the Main slider is take the red wires on BOTH sides and connect them together, then do the same with the white wires and finally with the black/ground wires. Do not short black to white or red to white. Red to red, white to white, black to black, and test. The Yamaha I have was a MONO device so it was wired differently so shorting 2 points worked there. In your case you have a stereo IN and Stereo OUT set of cables on a dual channel volume pot. Connect these as I have described only AFTER you determine the Amplifier works. THEN if connecting those of the main still yield no result, LEAVE them connected. Now do the same for the next sliders, desolder the wires, and connect them together as prescribed here and that is how you bypass these sliders.. If you still do not get sound, then I can officially say, I am stumped lol!

Edited December 7, 2022 by pianokeyjoe
adding more info.

[CYBERYOGI =CO=Windler]

If a keyboard with headphone jacks makes no sound, always check if the switch contact inside the jack is oxidized. In 1980th Farfisa/Bontempi stuff it is a common fault that the amp stays mute because it behaves like headphone is plugged in and so mutes the speaker.  You may need to desolder and dismantle the jack for cleaning.

[CRABFLAG]

KEYBOARD UPDATE:

      Again, I have been busy for the holidays, so I have not had much time to work on the broken CT6000 but I found another one locally and was able to get it for $150. Which in total $175 is not bad for two vintage Casios. I have not tested everything but this new one seems to work. So maybe that will help me in some way with working on the broken one. 

[CRABFLAG]

Also, I think I have tried every output including the headphone output so it is a problem happening before that part of the keyboard. 

[CYBERYOGI =CO=Windler]

Here is the Casio CT-6000 service manual:

https://www.file-upload.net/download-15065480/CT6000_SM_CASIO_EN.pdf.html

 

 

Edited December 26, 2022 by CYBERYOGI =CO=Windler

[CRABFLAG]

On 12/25/2022 at 10:45 PM, CYBERYOGI =CO=Windler said:

Here is the Casio CT-6000 service manual:

https://www.file-upload.net/download-15065480/CT6000_SM_CASIO_EN.pdf.html

 

 

The link did not work for me. The website seemed sketchy. But I think that would be helpful for me. I’m now thinking it is the melody volume slider and an issue with the amplifier. 

[pianokeyjoe]

13 hours ago, CRABFLAG said:

The link did not work for me. The website seemed sketchy. But I think that would be helpful for me. I’m now thinking it is the melody volume slider and an issue with the amplifier. 

Hello again!, the website is only a file hosting site. I downloaded the pdf in Linux on Firefox. It is fine. You need the service manual trust me.

[Helfried]

CT-6000 service manual

 

Here is the service manual - it is indeed detailed, the complete circuit is included and many hints for measurements and adjustment.... However, the layouts of some boards are missing, but they have not been forgotten, as it looks like they are also missing in the original. In any case, it is very helpful.