Casiotone CT 6500 - Turns On , No Sound

[HAILHAIL]

I recently adopted a Casiotone CT 6500, it turns on but no sound. Any advice would be great, thank you in advance. See link for video clip turning on the piano.

https://drive.google.com/file/d/1dEiWn3EapZ-LyJVCrtjLlA3GhkXjrrXB/view?usp=sharing 

[pianokeyjoe]

I saw a strange audio cable sticking out under the flip panel, is that supposed to be there? Or was that a cable you where using to try the outputs and it did not work with the headphone/output jack either? These units have been know to have issues with both the power supply and amplifier section since both are close to each other inside a tight plastic case. Do you smell electronics or ozone in the air when you turn it on? If you put your ear to the speakers, do you hear static,hum, or crackling? And lastly, if you have not tried it yet, try the headphone jack. Also, slide and wiggle the main volume slider as that will sometimes cause this issue. I know, cause I was just working on a church organ tonight with volume issues.

[HAILHAIL]

Thank you for posting a response.

 

The cable is just set there, nothing to worry about. So all I hear when turn it on is the slight static-pop of the built in speakers (can also hear it in the headphones when turned on) a very quiet hum that settles within a few seconds. No scent. 

 

Opened it up, see link below for images. Any advice before I open it up would be appreciated. - Thank You 

 

https://drive.google.com/drive/folders/1bE3Uwe8neBlJm4LauS_qqzhyq1xDduCx?usp=sharing 

Edited December 9, 2021 by HAILHAIL
Added Images

[pianokeyjoe]

Ok, I did not realize there was a lithium battery in these Casios! Ok, first thing, that battery needs to go, and you solder in a coin battery clip instead that you can then buy and insert a CR2032 coin battery. These last about 1 to 5 years depending on the brand.  Look close on the main board that the battery is on,for cracks,battery leak acid on the traces of the board(green side with copper traces, you would see blackening and crud or crusting on the board near the battery). The drums do not play either? There is a board you did not show me.. the AUDIO AMP board with Jacks.. That amp has been known to go bad over the years to overheating. The AMP board has the big aluminum heat sink attached to some power amp chips.Also, be sure to check that the cables from the amp board did not become detached from the boards. While a dead battery will not necessarily cause the no sound on THIS model keyboard(it will for the CZ101 internal sounds), it can leak and cause damage that way. I suspect a crack on a board, or the amp board having faulty output chip or the ironic loose wires scenario. Be slow, be methodical and be patient when you check everything. Its worth it. I did not see anything obvious on the component side of the boards you took shots of. Check the green side of the boards for crack, discoloration of traces due to the leaking of battery acid or maybe even a loose capacitor or other component due to a bad or old solder joint.

[HAILHAIL]

Uploaded more pics of the boards.

 

I can see the battery is mounted to some clip away from the board, it seems glued to it. Not sure how to replace it, I have the CR2032. No leaks, cracks etc.. anywhere I can see. I will keep looking more closely. 

[pianokeyjoe]

Firstly, THANKYOU for the followup pics. You will be happy to know I found your issue. Second, the battery is soldered to the main board not glued. Do you know anyone that works with electronics? Not electric, but electronics? The battery would need to be clipped off the board and then you need to desolder the leads that are left in the board or you can solder a coin battery clip to the remaining part of the battery leads left on the board to then slip in a new coin battery. Now for the real fun part.. The volume control near the RIGHT SPEAKER is cracked and you need to fix it or replace it. Check the area again, you will see it. Right near the last blank C key underneath inside the keyboard you will see a long narrow board with little white and red wires attached to it. That board is broken which is you main volume and as such is what is causing the no sound. Sadly seems that MOST of the board is smashed and ALL of the volume sliders are nonfunctional as a result. That board has to be seriously fixed with jumper wires to fix the broken traces OR, you need to find a replacement board or adapt a way to control the volumes somehow. I am assuming you are NOT living in South Western Pennsylvania?

[pianokeyjoe]

The part you need is Casio M5157

[pianokeyjoe]

Put your keyboard back together carefully, and store it in a safe place for now. The picture you need to submit to a tech if you do not live close to me, is pic: IMG9323.HEIC and focus on the bottom left. The damage is there.

[IanB]

Agree with @pianokeyjoe, the controls board has a lot of cracks in it it. If you can solder, you can fix it by soldering jumpers across the breaks; you'd also want to to mechanically repair the board too. The battery doesn't matter right now, the 6500 will work without it.

 

Also, as and when you do get it working, you might be interested to know it's possible to fully edit the current patch (though not save it to a preset) via MIDI. I wrote some software specifically to achieve that; see the link in my signature.

[HAILHAIL]

Apologies for the late reply, I am limited on how may responses I have in one day. THANK YOU GUYS for taking the time to pluck out all the details. I have some keyboard buddies that will let me know whether or not to fix the keyboard or buy a new one, I'll farm the work out to one of them here in San Diego. 

[pianokeyjoe]

Doh! wrong South western lol! Ok my friend, good to hear you have some back up! Hope you can fix it, it is worth it if you are a Classic Casio lover.

[Chas]

As the CT6500 is pretty much a preset version of the CZ Phase Distortion synths, it might also use the same output relays that have been known to fail in CZs and cause similar issues to yours (poor/ low volume/ no volume/ crackly output).

 

They're fairly easy to replace and have fixed many a CZ with output issues. The link below will show you what to look for in a CZ-1, so have a look on your 6500's boards see if you can find something similar. If you do, then replacing (or cleaning them) may get your 6500 working again. 

 

http://youthvulture.blogspot.com/2013/11/casio-cz-1-relay-replacement.html?m=1

[pianokeyjoe]

Hi @Chas! He did take some very good shots of the inside of his unit and I found the issue. It it the long volume control board. It is destroyed at the end near the right speaker. He needs a replacement board or some one to jumper the broken pieces OR, just solder the volume pot wires for the 3 volume controls to MAX volume or adapt new volume pots directly to the wires instead of the circuit board(like happens with amps and guitars). I have the replacement part but my unit is not readily accessible at the moment.

[IanB]

@HAILHAILIt's certainly repairable, it isn't a "beyond economic repair" situation, any reasonably competent technician should have no problem with it. Doesn't even need any parts beyond solder and superglue

[Aaron Wright]

Hi,

 

I'm the new owner of this CT-6500, and I spent the last few days disassembling, soldering, and experimenting to see if I can get it working. I'm not sure if it's against forum etiquette to continue the thread like this instead of making a new one, but I figure it makes sense to keep the current discussion in place and add on to it. I'll move it to a new thread if anyone raises any objections.

 

Anyway, I fixed the broken board and confirmed with a multimeter that the sliders are now doing what they should. Unfortunately, the speakers/headphones/line out still only produce a hum after starting, and generate no sound whatsoever regardless of volume. I even experimented with the aforementioned relay, finding that the contacts were stuck in the wrong position, hence the pop on startup, and I even tried bypassing it to see if that made any difference, but it doesn't seem to be the source of the hum or the lack of sound.

 

I found the service manual for the CZ-1, since I couldn't find one for the 6500, and thankfully the relevant components are almost the same, so I tried following the sound generation backwards from the output to find a place where I could actually hear some keyboard sounds, and there's a loss somewhere after the BA9221 DAC and the several TL082CP op amps at the top left of the main board (M5157-MA1M). I can hear some choppy and not-yet-completely-analog sounds from the output of the BA9221, which get quieter after the first op amp (which seems... wrong) and eventually gets lost entirely as I move further down. Part of the problem could be that I'm testing it with an 8 ohm impedence scrap speaker with the negative terminal hooked up to the chassis ground, which might not be the proper way to be testing the op amps further down the line, but I haven't found any guidance on how to do it better.

 

I also tried fiddling around with the DAC offset voltage, which didn't do anything and I'm not even sure I was doing it right since the components on the CT-6500 are labeled differently from the ones on the CZ-1. There is an adjustable dial right by an 8A9221 and TL082, but it's labeled VR2 instead of VR3, the voltage between pin 13 of the DAC and pin 1 of the op-amp is something closer to 5V than the service manual's specified 3 +/- 3mV, and adjusting VR2 has no apparent effect on the voltage or the sound of the keyboard.

 

Anyway, I poked around in the wrong place and now don't get any speaker output because I think I fried an op amp, so I'm going to swap them around on the board tomorrow and see if anything changes. I am also suspicious of the two chips labeled "5K4 T / HD14051BP", the functions of which I am uncertain.

 

Just spitballing here, but the hum from the speakers/headphones is exactly the same as the sound produced by putting the negative terminal of a speaker to chassis ground and just poking around until I find a positive lead somewhere on the board, so that suggests it must either be a short somewhere on the main board, a problem with the power board (maybe the transformer?), or this is normal noise that's ordinarily supposed to be removed by all the sound processing circuitry. I suspect the transformer, just because I own an electric piano with a buzzy/static-y speaker that sounds similar, which I was told could be an issue with a transformer. Also, the shattered volume control board is on the same side as the power board, so even though there's no apparent damage on anything else, it's not outside the realm of possibility.

 

Sorry for the long read, but hopefully someone might have a better clue than I do from all that information, since this is my first time diving into a Casio or doing any significant repair work on audio circuitry, though I do have some basic familiarity with audio circuitry from digging into a different keyboard for a personal project a while back. Is there a particular direction I should be focusing on here (the power supply vs the DAC on the main board)? Really hoping to get this thing working as more than a midi keyboard and to hear its amazing sounds, and I'd even like someday to try hooking an arduino up to this thing to get more individual control out of the phase distortion synthesis than the presets it offers, if possible. But I digress. One thing at a time.

Edited January 2, 2022 by Aaron Wright
Clarified plans for op amp chips

[IanB]

I would urgently advise that you stop testing immediately with a speaker. A speaker is low impedance (8 ohms) which requires far more current than signal level circuitry is intended to provide (it's also an inductive load) and can cause damage. The fact that now you're not getting sound where you did before means some more damage may have occurred. You *can* do a similar audio test method by using a lead connected to the line level audio input of an amplifier with the test end plug stripped off and the signal wire as your probe and the shield grounded, I've done this myself. But under no circumstances use a speaker.

 

I would also strongly advise against swapping op amps around on the board. These are old parts already, and you don't know whether the one you swap in is faulty. TL082s are cheap as (er) chips and if you're replacing one, always use a new one.

 

The 4051s you're uncertain about are analog switches https://www.ti.com/lit/ds/symlink/cd4051b.pdf which function as the expander circuit to give a pseudo-higher resolution to the DAC output. Depending on what you meant by "choppy", that may indicate a fault there. There's also a 4053 or 4066 (should be somewhere nearby) which may be suspect.

 

It would be good to see some audio traces; since we're in the audio range a computer or tablet oscilloscope app would be able to do that- again using a stripped lead as an input.

 

Finally, there's no need to get an Arduino in there. Because the sound generation is all done inside the custom chips, you can't get "bend" any more capabilities. You can complete edit the active sound via MIDI, including those in MIDI multi-channel mode (where MIDI channels 1-4 act as 4 separate synths and Channel 5 is the drumbox). My software VZV-CZ is purposely designed to work the CT6500 (it's actually why I initially wrote it), link in my signature

 

Edit I've included the CZ5000 service manual below, which is closer than the CZ-1 to the 6500. Also, I found that the pinouts on the sound generator chips UPD933 are different on mine to the ones in the manual. Please be very cautious about fiddling with them as they are irreplaceable (without a donor CZ).

CZ-5000_cascz50sm.pdf

Edited January 2, 2022 by IanB
Added some stuff

[IanB]

Additionally; the drums are not generated by the 933 chips and are on a completely different PCB (whose designation escapes me, I don't have my machine in bits at the moment) but it's the same one IIRC as the chorus unit is on. So if you can't hear the drums, something way downstream of the CZ phase distortion gubbins is at fault. So the best place to start is there; get to a state where we can hear the drums. Until that point is reached, we can stop messing around with the PD board.

[Aaron Wright]

Evidently I've had the concept of impedence wrong in my head for a while, so thanks for the tip. I somehow got it in my head that the impedance would have just resulted in a quieter speaker and a lower likelihood of blowing my eardrums out when listening for a tone. I've learned my lesson.

 

The op amps I was swapping are the cheaper TL082s, which was why I figured it would be alright to swap them. Mostly, I got carried away and desoldered them with the intent to test them individually, but thought it would be easier to see if swapping them changed the point of failure and probably wouldn't hurt anything. Worry not though, I was being extra careful with everything irreplaceable.

 

The "choppy" sound was what I assumed was the sound going into the expander circuit, since I did read up on that in the CZ-1 service manual (thanks for the CT-5000 manual, by the way) and it was coming out of the op amp directly after the DAC and before the 4051s. It sounded like I imagine the unexpanded waveform printed in the service manual would.

 

That midi info is excellent and is exactly what I was interested in doing. Pretty incredible that that much control is available through midi alone, as someone whose only previous experience has been with some comparatively dumb keyboards. I'll definitely be using your software!

 

Finally, I did read about the separate drum synthesis, but wrongly assumed it was still on the same board. There's no sound from the drums either, so I guess I'll have to poke around (less literally this time) the spooky power board. That transformer is MASSIVE! I'll update as I find out more and hopefully don't get zapped by any capacitors.

Edited January 2, 2022 by Aaron Wright
missing a word

[IanB]

HI Aaron,

 

Regarding the MIDI- I was going to go down the Arduino/Microcontroller route until I did a lot of experimenting and found it had the full MIDI implementation. The trick is that on all CZs, the live sound is editable at Patch 96 (60 hex) and the CT is no different, including in multi-channel (multi-timbral) mode. It actually implies this in the user manual in the MIDI implementation chart, but then they give no useful information so it's the kind of info that's only any use if you know it already! You can upload and download patches at will (none of the CZs have a true MIDI parameter editing mode, they all require you load the entire patch each time you externally tweak a parameter).

 

Have you ever got any sound from the op amp after the 4051? Note that there's another analog switch (probably a 4053 if it's the same as the 5000) which is doing the sample and hold which samples the output between DAC value changes to prevent glitching. It may well be worth just swapping the analog switches to see if that helps.

[pianokeyjoe]

My good sir, have you explored the Audio AMP board as I had mentioned before? The Synth and Accomp boards, IF they are intact and have no burnt or loose components(cold solder joints), should not be your main focus. You stated all the functions of the keyboard worked before just no sound. We found the volume control boards smashed which begs the question, why was that section smashed like that?? So thinking along those lines, you have to assume you are dealing with physical damage, and the damage extends beyond the volume sliders board. Your power supply and amp boards are BOTH near the section that is damaged. I can confirm from my own CT6500 donor keyboard, that if you remove the amplifier board from the keyboard, you still have functionality of the controls, just no sound obviously. My donor unit had a bad amplifier section with all the sounds being very distorted and loud which means the filter section died on mine. The amp board has a big heatsink connected to audio output chip or chips. And yes, the PSU is massive too. Check both of these boards and parts for cracking or loose components that may have come loose due to physical trauma. You would have to look very carefully at the solder side of both boards. Yeah never ever use a speaker to test sensitive circuits. If anything a simple multimeter will suffice. Though if looking for sounds like I have had to do on some of my other fixer keyboards, checking and fiddling around the amplifier board would be my first place if the unit turns on, and all the controls work and react to presses.. The o-scope method is even better! what would you use as the o-scope input in the computer though? The audio mic pink minijack??

[IanB]

@pianokeyjoeYou'd normally use the line level (light blue) because the mic input is designed for electret microphones and has a low voltage DC to power them, it wants a small varying capacitance as input, not a voltage. Or a cheap USB input like a Behringer UCA222 if there's no line in.

[pianokeyjoe]

9 minutes ago, IanB said:

@pianokeyjoeYou'd normally use the line level (light blue) because the mic input is designed for electret microphones and has a low voltage DC to power them, it wants a small varying capacitance as input, not a voltage. Or a cheap USB input like a Behringer UCA222 if there's no line in.

Ah ok thankyou @IanB! My laptop and industrial all in ones only have the green speaker and pink mic ports sadly. My heavy bulky towers all have the extra ports though. Yep I may need to find a cheap usb external solution if I do not want to setup a space for a big bulky tower,monitor,keyboard,mouse setup in my very very limited space. I have been using my dresser or washing machine as my computer test desk for those towers lol! But yeah, it makes sense to use line level. Like phono input versus aux input on a old stereo system! So I only noticed that Aaron Wright is the NEW owner of the keyboard in question so he may not be privy to the pics the former owner sent us.. But just the same, I hope those op amps did not blow.

Edited January 2, 2022 by pianokeyjoe
misspelling

[IanB]

@pianokeyjoe I just tried looking at the pics and they're still working.

[Aaron Wright]

As a newbie, I am apparently limited to two posts a day, so apologies that my updates will have to be portioned appropriately. Anyway!

 

I resoldered the TL082CPs in a different order, and it turns out I was wrong about there no longer being sound output-- it's the same as always, though the hum actually seems quieter than it was in my initial testing.

 

I looked closely at the power board and didn't find anything loose, though some legs of one of the transistors were apparently cracked around the solder pads, so I reflowed that solder and several others just to be safe. I'm actually considering reflowing every single soldered connection on the power board simply because there aren't that many of them and it might help, but I'll only do that if I run out of ideas. I also looked at the amp board for similar issues but found none.

 

I found a USB sound card I had laying around and used the line in per @IanB's suggestion, which has been interesting and enlightening. The "buzz" everywhere is exactly 120hz, which suggests yet again that it's something in the power board, but I'll have to look closer into that. Here's the waveform, if you want to see:

 

 

It's about the same at every point with positive voltage that I test, going back to the power board, but I'm reluctant to poke my "line in" input around the power board because I don't want to fry my sound card if I poke the wrong part, so I'm not sure precisely where it starts. All sound coming from the board is mixed with this waveform, it's never just the sound on its own (save, perhaps, for pin 1 of the BA9221 DAC, though I think that's mostly due to the much higher voltage).

 

Secondly, I found that drums sounds are being produced correctly and are making it to the amp board. The same cannot be said of the keyboard sounds, which don't make it out of the main board. The top left op-amp, TL082-2, seems to be where the sound stops, and this is one I swapped out from TL082-3 down lower. I think that suggests that that might be a problem piece. I can get sound from the non-inverting input, but none of the other pins. I measured some voltages:

 

Pin 3 (non-inverting input) with no sound: 5.70-5.72V

Pin 3 with sound: same as above plus 2mV

Pin 2 (inverting input): constant 4.22 volts

Pin 1 (output): constant 13.64V regardless of sound

 

The other side of the chip has around 200mV on all the input and output pins, which does vary with keys pressed, but I can't hear any sound out of them (probably due to the... low voltage). To reiterate, there is no sound from the keyboard past that chip. It could be that TL082 is at fault, or possibly the 4053 below it, or maybe even the 4051, if they're supposed to contribute anything more than an audio output signal to the TL082.

 

Finally, the sound output on the amplifier board seems to stop at the NJM13600. Both input pins on both sides (total of 4 pins) have drum sounds on them (but no keyboard sounds) and neither of the outputs produce anything other than the trademark buzz. There is no sound from any of the other pins either.

 

So, to summarize, I think there are three problems:

 

1 - 120hz buzz from the power board

2 - no keyboard sound past the second op amp on the main board

3 - no sound at all out other than buzzing from the amplifier board, stopping at the NJM13600 amplifier.

 

Tomorrow I'll continue to read the service manual and see if I can figure anything else out or narrow down the issues any further, concentrating on the hum and the power board first and the amplifier circuit second. Thanks for you guys' help as always. I might update this post with new information if anything else comes up, but we'll see.

[IanB]

Okay, interesting. A quick suggestion here would be that the 120Hz buzz would strongly point towards power supply smoothing caps (i.e. big electrolytics) having lost their mojo and need replacing. They're over 35 years old now so that would be quite expected!

 

Also, the 4051 is in the negative feedback path of that TL082 and the 4053 is enabling or disabling its output to the next audio stage, so I'd suspect them as well. They're easily sourced and cheap.

Edited January 3, 2022 by IanB