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pianokeyjoe

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  1. @Chas and @CYBERYOGI =CO=Windler beat me to it! Yup! Check the yellow rectangle capacitor and check that your local input AC wall power voltage is set firmly on the correct setting. Then the black square device just down of the yellow rectangle capacitor which is your AC/DC full bridge rectifier, could be shorted and thus dead. That WILL cause the mains fuse to blow. The rectifier is a set of those black and silver diodes you would find in AC to DC power adapters but in a solid package. If ONE of the 4 diodes inside that device is shorted, the whole thing is going to be shorted.
  2. Remember when doing your troubleshooting that the CT6500 has built in speaker system and the amplifier and PSU sections will be different due to this fact. The synth/accomp section is also different from the CZ line due to the added rhythm/accomp section. The presets are but 40 in all and there is a hidden rewritable internal sound preset that is only accessible via midi as @IanB has pointed out. This keyboard is very different beast from the CZ line. You will need to do some process of elimination troubleshooting as you have been doing, for sure. I do not have my units handy still so I can not add more info to help but this: The PSU may need to have caps redone! I smelled electronics when I last powered my 2 good CT6500 units!
  3. Is the DAC chips on the amp board?
  4. Sorry @Aaron WrightI had to google the part number for the DAC lol. Ok, so after you showed the expander circuit which I find baffling why a dac and then an expander to get the analog sound out of the digital waveform in the first place but eh.. Casio and Yamaha did things different in the 80s to get that magic signature sound from their keyboards. Ok, So the first thing I thought was the DAC is bad because duh! You getting digital sound where analog is supposed to be AND the digital sound artifacts of pressing more than one key, which is fuzzing, but louder than normal sound volume. So check the DAC chips. You should have 2 at the very least, on the main or melody sound section, one on the rhythm section and normally on most classic Casio accompaniment keyboards you would have the third for chords/bass/arpeggio? I could be wrong. I do not have my board accessible still and it is 2024 going on 2025.. I am slacking, I know, Sorry. I can 100% tell you when I changed my amp board out, the problem went away for ME. So at least in my case, the issue is ON the amp board..
  5. Hello @Aaron Wright! I check the forum classic Casio section several times a day for years now so you are not writing in a dead thread by a long shot! So your situation is the same as mine for ONE of my 3 CT6500 units. It has a bad AMP board and that is very easy to tell IF you had a second unit that does work but say, has broken external parts and you would just transplant the good amp board from the physically damaged(in shipping in my case) CT6500 into the CT6500 that has everything looking good but needs a good amp board.. The issue in your case is that very thing.. bad amp board. Sadly if you do not have more than one unit, you will need to fix the amp board you have. Best thing to start with is finding the Filter and DC bias section of the AMP board. Leave the big Synth boards alone except for the CR2032 battery inside, you WILL need to get rid of that and put in a coin battery holder in it's place with a new battery! The Dead Battery can and will cause issues if left in the synth/home keyboard CT6500. That fuzzing output is the filtering section and DC bias being off due to some short or in my case, an open resistor somewhere. Again that sound is what you get from the synth chip in raw form. You need the biasing and filtering to tone it down to analog warm sounding levels. Even then, you DO hear the digital artifacts when you press certain presets without pressing any keys yet, and when you release keys after hearing a tone(Normally the same fuzzing but very very quiet and you have to put your ear to the speakers to hear it). Yamaha FM synths and keyboards have this same fuzzing artifact in their preset tones after key release or when you press the touch responsive keys very soft you hear it too. I hope you can get your unit fixed cause it is a very nice preset based CZ style keyboard, not unlike the CZ230S and maybe the CT5500?? Oh the battery in the CT6500 is for storing a custom synth sound you can make via midi and if I remember correctly, the internal recorder? I could be wrong on the recorder though.
  6. Glad you did a more thorough investigation and got it resolved!
  7. Hi, firstly check that you are using a NEGATIVE TIP CENTER polarity 7.5VDC or 9VDC power supply with at least 500mA. Thats the first thing. ALL older CASIO keyboards use NEGATIVE CENTER PIN polarity power supplies, no exception. Once you have tried to use the properly negative polarized power supply, the next thing to check in the jack itself and the solder points on the jack. You WILL notice solder pad/pin lifting if the jack is loose or wiggly or a hairline crack around that area of the board. The next thing is the most obvious.. the battery compartment for corrosion and greenish or brownish corrosion spots on the boards. Then check the clear mylar flexi ribbon cables that connect between the POWER/AUDIO AMP board and the main BIG SYNTH board. The most obscure thing to check as I have indeed checked this before and was lost as to how it worked but indeed it WAS my issue on a CZ101, the POWER SWITCH section! On the MT800 I believe the switch is a single reddish color switch on the side cheek of the board? I could be wrong but check. That switch has several things goin on besides a simple make or break 2 wire circuit for power. It has several circuits that also redirect battery power and the auto shut off feature and power led signal.
  8. Thankyou @Chas for directing him to the downloads! @boilive, yes the filter block right before the amp section. So the synth output at the sound generator is sounding very distorted but you can play nice funky stuff with that. In the case you are not happy with that though, I would say the sound you hear is the digital aliasing that you would hear if the synth is operating normally and you would have to put your ear to the speaker after you release keys, and you would hear that same distortion but very very low. So yeas, it is a filtering circuit issue. Anti-aliasing or aliasing reduction area of the circuits would be a good place to start your trouble shooting. I broke a pin on my main ic SOC on the MT45 that put it in that state permanently until I put a resistor in another part of the circuit to restore it back to normal.. I do not remember how I did it or the circuit I "patched" since I was still a teenager when I did that waaaay back in 1988.
  9. Huh! Funny, I remember making my CT310 and MT45 make those distorted sounds by shorting pins on the main IC chip but I never did it on my MT65s or CT405. I would say the traces from the Sound gen chip to the amplifier ic need checked. There is a resistor that may be either shorted or in more likelyhood, broken(open). The distortion is the filtering section of the circuits. Right now I am in the middle of a crisis but someone here could help with the service manual which IS posted here!
  10. google Casio CPS101. I found the manual at archive.org and have it in my hard drive now. Download the PDF file version and check page 14. That gives US, not just you lol!, the info needed for us CPS101 owners to set the midi channels, local control on/off and so on. YES, you have to press a combination of buttons to get those settings set. Not for the faint of heart I will warn you.
  11. Do you have the same issue? A key lifts up? If so, see my comment above and the picture of the keys. Ebay search CZ101 keys if you want to just buy a replacement, or syntaur.com as well in the USA, for such replacement.
  12. From my hacking of Casios experience in the past, The key scanner/matrix chip in most Casio keyboards of the 1980s had a maximum of 8 notes polyphony play possible.. I do not think this was a fault but a design feature back then. The sound engine was capable of 16 note poly via a midi controller or sequencer or some other device capable of more polyphony but as my old MT240 keyboard goes, it only has 49 notes keyspan even in midi mode, and 4 part midi channel play via midi tone module mode, but the keybed in the MT240 has a 10 note poly play capacity. So limitations in the design of the keyboard are at play. Casiotone all the way back to the late 70's had 8 note poly play sound engine based keyboards and that seemed to be the limit with the key scan/matrix ic and supporting circuitry. I do not know if the FZ1 and VZ1 had this limitation however.. As those 2 keyboards were made with a very different keybed(both units had the same semi weighted synth bed), and were made in 1987/88? The CPS line of electric pianos did have more polyphony at the keys but again.. the key matrix is different even from the CZ1 which is velocity sensing. I could be wrong there but I say to you, the limit is down to the keybed ic chip and circuit design, not the internal sound engine. Some one else with more in depth electronic experience will be able to delve in deeper and better explain this.
  13. Ok, remove the main board which you showed us which is still fixed down to the plastic casing, and check underneath that big board for discolored traces and corrosion. That board is the one near or on top of the battery compartment from the video shots I saw. So the DG20 seems to have 2 bigger boards. The loose one that is smaller and has a reddish card board on the back of it, also needs to be checked. You will need to remove the red card board to see if the traces on that one are corroded or not. The no power thing really is a dog of a situation as I have 2 PT20 units that while they do power on, no sound or bad sound. All due to batteries leaking inside so yeh, do not take anything for granted. Also seems like with my PT20, you may have shorting at the auto power off circuit or if, there is a p-reset circuit on the DG20, that circuit may be tripping due to acid/alkali. At this point, it does not hurt to check.
  14. Ay ay ay.. Ok, yeah I fear damage from the old batteries. Pictures can help to point out anything you may miss. I can tell you that even clear battery alkali film on the circuits WILL cause trouble even if you can not see obvious issue. The boards do have to be cleaned but I myself still do not know what proper mixture of stuff is needed to clean battery alkali and acid off circuit boards to bring our precious Casios back from the dead.
  15. Corroded DC power barrel or the power jack on the DG20 itself? Check your battery compartment for such obvious corrosion as well. If you see that in the battery compartment you can bet the inside electronics maybe corroded by the leaking batteries that were in the unit. Now the biggest issue is that most modern batteries being made in Mainland China, the quality and volatility of the battery chemicals inside are sub par and very dangerous too. I have SEEN it first hand and wow, scary! So you may have a dead DG on your hands. Check inside for corrosion on the circuit traces on the boards inside. Report back
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