Casio CT6500

[pianokeyjoe]

So, I finally got to plug in 2 of my beloved Casio CT6500 keyboards in today since I reorganized my future music room. And I have some worrying observations.

1) I plugged in one keyboard that used to work, and now it hums really loud and no sound comes out but all functions respond to button presses.

2) The second keyboard plugged in is fine, all sounds and functions are a go, BUT there is this smell of electronics coming from BOTH CT6500s I own. I did clean the contacts for the volume sliders on BOTH units back in 2018-19. These were BOTH working back then but now in 2021, I notice these anomolies(smell of electronics, and with the second unit, no sound but a big hum).

 

Has anyone else experienced this? I have a third unit with a bad amp board, and broken buttons but working mainboards,etc.

Is the AMP board in my HUMMER the culprit? These suckers are LOUD when turned all the way ON, so that is nice, but damn.. 2 bad amp board CT6500s? And the good unit smelling like electronics too? Ay ay ay!

 

Any clues? I know how to fix them but is my good one about to bite the dust now too?

 

See? So many questions, so little answers lol! I think I need a service manual here..

[IanB]

I've never found a service manual for the 6500 (come on Casio, release them all!) but much of it is very similar to the CZ5000 in the guts! Humming does sound like the power supply/amp having gone down, might be a capacitor thing (or might not, hehe). Does it sound like mains frequency?

 

What does electronics smell like? Magic smoke about to be released?  I'd personally be tempted to get in there with at least a multimeter and preferably an oscilloscope before switching it on again.

 

 

CZ-5000_cascz50sm.pdf

[pianokeyjoe]

Hi IanB! Yes it sounds like mains hum but very loud, I guess going through the amp speakers. The smell of electronics is like it was washed in a chemical and kinda newly soldered? But can be like burnt phenolic board smell too? I am checking them both later on this weekend. I can not have both units go down. I do have a third parts unit with a bad amp board that makes all the sounds very loud and grungy distorted(feedback). But here is another detail I failed to mention: The HUMMER's flip lid does NOT tilt all the way to 105 degrees back, like the working unit. The lid is supposed to tilt back to 105 degrees in order to hold music sheets/book, and stay open and not slam down on your hands. The Hummer stays a 92 degrees.. almost a 90 degree tilt that any sudden or strong playing can send the lid slamming down on my hands. If I try to push it back more, it wants to bounce back to 90-92 degrees and will pull on the top chassis. I am not sure but I think a wire harness is jammed in the pivot of the lid.. a darned, cliche techno lazy diagnostic "LOOSE WIRE" scenario lol! I will not know for sure till I crack it open but the third parts unit did not get put back all the way together due to the fit being so tight and those wires getting in the way of the darn lid too. The working unit I have NEVER had to crack open so no issues but the smell is worrying me yes.

[IanB]

@pianokeyjoeWell the lid at least is easy! You just slide forward the covers at the ends of the lid and that exposes the mounting, you can then undo the two screws each side to remove the lid. The only wiring in there is one connector for the tweeter each side in the lid which can be locally unplugged. Then the lid just lifts off.

[pianokeyjoe]

Ok! I shall see what to do here in a few days. I am still organizing and have ALOT of keyboards to move around and no real space to setup and tinker. Been using my laundry room washer machine as my tech bench for some of my projects.. The only area well lit and free of stuff lol. This sure helps alot though. It may not be the lid pinching a wire or two then. But.. then again! If you short the tweeters, that would cause the amp to blow too so a must check situation indeed.

[Chas]

On 4/8/2021 at 4:56 AM, IanB said:

Humming does sound like the power supply/amp having gone down, might be a capacitor thing (or might not, hehe). Does it sound like mains frequency?

 

FWIW, my Casio CT403 had an annoying output hum, and one day a RIFA film capacitor near the PSU decided to commit suicide in quite a spectacular fashion - lots of smoke and the 403 dying on me!

 

I replaced the RIFA capacitor with a better quality item and not only did that bring the 403 back to life, it also eradicated the output hum.

 

No idea if the CT 6500 uses RIFA capacitors, but if it does it might be a good idea to replace them as they're known for going pop as they age.

 

On 4/8/2021 at 4:56 AM, IanB said:

What does electronics smell like? Magic smoke about to be released?  

 

With my CT403, the magic smoke about to be released was because of a dying RIFA capacitor. And the electronics smell is a combination of hot plastic, solder and heatsink paste 😉

[IanB]

@Chas Ah yes, the RF caps are really just little time bombs put there by the manufacturer! "Hmm, let's set this one to 32 years, 3 months and 5 days! HAHAHAHAHAAH!"

[Chas]

@IanB- I believe that the Germans actually call them "RIFA Bombs"! 😂

[pianokeyjoe]

Hmm, well that doth blow the big one then now doesn't it?! I have a alot of keyboards lol! So I will have to setup a tech bench and buy ALOT of caps to replace one keyboard at a time. Mind you, that is only if indeed my issue is the caps. I have to check but right now I have put up the keyboard to wait until I have a physical space to setup a tech bench and trouble shoot and fix this. Thankfully I have 3 keyboards like this to make ONE work good at least. Thankyou for the service manual pdf btw!

[IanB]

The RIFA caps are RF suppression caps strapped across the mains input and they do tend to blow spectacularly as a result. They don't tend to damage anything else when they blow except by blast damage, but always take the fuse out. They need to be replaced with an appropriate X2 rated capacitor. The device will actually work without them but may put bad interference into the mains and upset nearby radios 

 

With the age of these keyboards it may OTOH be the main decoupling electrolytics causing the hum.

[PinWina]

Hi!  I recently received Casiotone CT-6500 from a relative in order to learn the basis of the piano, and I have a problem.

 

When I play a chord (three notes)  if I start playing the main melody, some notes doesn´t sound, in fact is more like them sound very low, so much that you can´t hear them. After some investigation I could see that one note sound and the next no (for example, if I start the melody on C it sounds, D no, E sounds, F no, G sounds...etc. If I start in G it sounds, A no, B sounds...). I supose it's some synthesizer option, but after reading the manual, and trying diferent options I can´t find the solution. 

 

Sorry for my English and if this is not the right place for this question.

Thank you in advance.

[pianokeyjoe]

Hello, it is electronic issue with the key multiplexer chip. @CYBERYOGI =CO=Windlercould very likely help you there as well as @IanB with this issue. I remember it being reported here before. The sound chips(2 of them I think), output every other note each to allow for more polyphony and sound layering. Could be however, a simple issue of the main volume or melody volume acting up on you which IS dual channel(stereo). Because you do say the you can play every other note, then try that once dead note and it plays but then the previous sounding note next to it does not sound, leads me to believe it is the audio volume line or pot(slider) being dirty or defective. I have 3 of these keyboards but I do not have immediate access to them right now to better help but at least this gives you a starting point

[CYBERYOGI =CO=Windler]

I have nothing about the CT-6500. The only somewhat similar keyboard I own is the CZ-230S, which has only one sound IC (Music LSI "NEC D933AC") and no "key multiplexer chip".

[IanB]

On 3/14/2023 at 5:49 PM, pianokeyjoe said:

Hello, it is electronic issue with the key multiplexer chip. @CYBERYOGI =CO=Windlercould very likely help you there as well as @IanB with this issue. I remember it being reported here before. The sound chips(2 of them I think), output every other note each to allow for more polyphony and sound layering. Could be however, a simple issue of the main volume or melody volume acting up on you which IS dual channel(stereo). Because you do say the you can play every other note, then try that once dead note and it plays but then the previous sounding note next to it does not sound, leads me to believe it is the audio volume line or pot(slider) being dirty or defective. I have 3 of these keyboards but I do not have immediate access to them right now to better help but at least this gives you a starting point

 

If you can hear the notes but they are very low, there's a good chance this is in the internal mixer (audio circuit rather than digital circuit) which should make it relatively easy to fix with appropriate test gear. Might be a failed op amp or even a bad DC blocking capacitor.