CT-403 Repair

[skizze]

Hey all,

 

I'm new to this forum, but I'm looking for help repairing my Casiotone 403. I accidentally knocked it over and it now no longer powers on. If anyone happens to have any experience with these and could point me in the direction of the possible components which might've failed, I would be eternally grateful.

[CYBERYOGI =CO=Windler]

This can be everything. May be a crack in the PCB (torn traces) or a switch or jack has ripped out of it. If a special chip cracked, it can not be repaired, but likely parts need to be soldered back in. If it fell on a plugged in plug, contacts inside a (e.g. power supply) jack may be bent and thus prevent it from turning on.

[Jokeyman123]

You will have to disassemble it from the bottom first, look for hidden screws if you can't get it apart easily. Now look for physically obvious problems. Might be a cable connector that's popped loose. Or as cyberyogi said, a crack in a circuit board.  You probably should use a good magnifying lens since even a tiny crack or broken solder joint could be the culprit and will be hard to spot with the naked eye.  If you had it connected to your power supply when it dropped, check the solder joints at the power jack first, this would be my first suspect. Let us know how you progress.

[CYBERYOGI =CO=Windler]

I see, the Casiotone 403 is one of the faux woodgrain models, which has an internal power supply and is mechanically different. It is likely mechanically similar like my Casiotone 401 (even same accompaniment chip).

The 401 is quite heavy (about 10kg?) because despite its case looks almost perfectly like wood, it is mainly made of plastic coated sheet steel. (Casiotone 201 and 202 were of genuine wood.) In spite of this it is not as robust as it appears, because at the corners of the side pieces (made of pressboard?) the plastic woodgrain tends to peel off. I had to hotglue mine back into place, but this sheet plastic stuff also cracks off easily when accidentally folded to hard. The high quality speaker sits in an own thick plastic compartment of that even the cable hole was sealed with glue to turn it into a perfectly closed box. It is driven by a large hybrid amplifier module that is screwed to a sheet metal heatsink welded to the case bottom. This makes it very unpleasant to remove the mainboard because you have to unscrew the module and mess around with (possibly poisonous) old heat conductive paste.

The front panel is held by screws (those in the 403 seem to be at the sides). I don't know how yours is built, but (if like 401) be careful with the 5 metal lashes with screw holes those hold the rear part of the control panel from inside. With case opened, these lashes are sharp as razor blades and easily damage the panel and PCB traces; with mine a preset sound LED failed by an accidentally cut trace after working on the opened keyboard. After soldering the trace I glued ribbon adhesive tape over the sheet metal lashes to make them less dangerous. After opening, a lot of broken small black rubber rings fell out of the case - likely they belonged under the piano keys somewhere for damping (keys feel a little loose), but turned brittle by oily room air or ozone.

I don't have a service manual of my 401, but got a photocopy of Casiotone 403, which was of great help to understand the general hardware architecture, because it has the same accompaniment hardware combined with the main voice section of Casio MT-60 (first 403 models had CPU version D776G with external bugfix circuitry). They are a good didactic example how Casio in early instruments made several different CPUs cooperate and combine their keyboard matrices rather than the centralized master-slave approach found in later hardware, and how despite almost self-contained CPUs often minor functions like clock rate conversion or preventing wrong key press order during preset sound selection used a crazy amount of "glue logics" ICs cluttering up the mainboard.

[roboshaman]

Hey, new here.. after removing the spring, how do the keys come off the 403? Haven't been able to find much about it. 

 

[roboshaman]

Never mind. Figured it out.

[johnbsa650]

Any contacts for casiotone 201 repairers ? I am in London

[Chas]

When I was in the UK, I used this guy, Mark Exnaw, to do work on my Roland JX-3P, including fitting a Kiwitechnics Kiwi3P upgrade. He did excellent work, is very fairly priced and is well known among the synth community. Nice guy too.

 

His Facebook profile is:

 

https://www.facebook.com/mark.exnaw

 

And his old email is:

 

Axa@onetel.com

 

Here's a Gearslutz link where you see him being recommended 👍

 

https://www.gearslutz.com/board/electronic-music-instruments-and-electronic-music-production/1047218-best-synth-repair-option-london.html

[TonyR]

Good day. My Casiotone 403 has a permanent tone of about 1kHz on the accompaniment side. I am an electronics hobbyist so have some hope of fixing it. I’m assuming a failed filter capacitor? Where do I start looking?
if anything me can let me have a service manual that will be great. Many thanks. Tony Roberts. Pretoria. 

[pianokeyjoe]

On 3/10/2017 at 3:14 AM, skizze said:

Hey all,

 

I'm new to this forum, but I'm looking for help repairing my Casiotone 403. I accidentally knocked it over and it now no longer powers on. If anyone happens to have any experience with these and could point me in the direction of the possible components which might've failed, I would be eternally grateful.

Hi skizze! Welcome to the Casio Forum! I need you to do as the other very helpful users have asked and carefully take the unit apart. Take pictures of ALL the circuit boards and power supply area so we can see where the damage might be and better inform you and others that may be in similar trouble, on how to repair it if at all possible. Thats the first step to save us all alot of confusion and speculation. The obvious, check the control panel for damage and the back where the plug and jacks go for damage. Then proceed to the dismantling fun! Pics need to be clear and big so we can zoom in on them. Now I just realized this post is very old. BUT, if skizze ever fixed it or not, remains to be seen eh? We can hope. So I will address this to all potential users then.. Check the obvious, then proceed to dismantle carefully and methodically. Taking real good clear large pics like a user of a CT6500 recently did and I was able to find his issue right away.

Edited December 30, 2021 by pianokeyjoe

[pianokeyjoe]

1 hour ago, TonyR said:

Good day. My Casiotone 403 has a permanent tone of about 1kHz on the accompaniment side. I am an electronics hobbyist so have some hope of fixing it. I’m assuming a failed filter capacitor? Where do I start looking?
if anything me can let me have a service manual that will be great. Many thanks. Tony Roberts. Pretoria. 

Hi TonyR! Ok, I need you to post a video of you messing with the keyboard,the tone, the volume settings,the rhythm buttons, the melody side, etc. Play the board like you are trying to play it normal, lets all see and hear what you got going on and we can further advise. Mind you, only if it is possible to film, if not, then do it old skool, record the keyboard with audio only and lets hear what is up. Lets hear the tone while you play the melody side and try to play Casio Chord section in Fingered, single fingered and manual bass mode as well as ACCOMP OFF with only the melody side up. Fidget with the volume controls to hear if there is static noise for the accomp side. Now I can tell you the chip for the accomp section IS different from the Melody so that is at least a good thing that if the chip is dead, you can still use the keyboard as a basic organ.

[TonyR]

Thanks so much. I’ve taken a video and will Now try to figure out how to attach it. In summary, everything works. Minor scratchiness on pots. The noise sounds like pure sine wave. 

[TonyR]

Still trying to send video. I don’t see an image other than a GIF allowed. I’m going to try sending the video to Flipboard then using the link. 

[IanB]

Hi TonyR, you can always put a video on YouTube so we can all see it?

[pianokeyjoe]

12 hours ago, TonyR said:

Still trying to send video. I don’t see an image other than a GIF allowed. I’m going to try sending the video to Flipboard then using the link. 

You need to do as IanB stated and use youtube or vimeo or some other 3rd party video clip hosting site as this forum will not allow uploading video clips so far as I have seen.

[Chas]

If you have a Facebook account, you can upload to your Facebook page and make the post sharable/ viewable by the public.

[CYBERYOGI =CO=Windler]

On 12/30/2021 at 6:39 PM, TonyR said:

Good day. My Casiotone 403 has a permanent tone of about 1kHz on the accompaniment side. I am an electronics hobbyist so have some hope of fixing it. I’m assuming a failed filter capacitor?

 

This might be a keyboard matrix (or LED matrix) scanning signal leaking into audio by a broken capacitor. (I don't know the actual scanning frequency of this model.) This is some 401 info I wrote for my site:

 

The Casiotone 401 uses the main voice CPU NEC D773G, which is an early member of the D77xG family. The accompaniment CPU "NEC D8049C 084" is an MCS-48 microcontroller with 2KB ROM (I dumped it) that controls through I/O IC NEC D8243C the chord section tone generator "Texas Instruments TMS3615NS", which is socketed by unknown reason. Because Casiotone 301 (same hardware without accompaniment) came first, it may be that a shortage of that IC prevented finishing the 401, so the TMS3615NS could be installed last when the rest was already completed. Someone e-mailed me that in his Casiotone 701 the rare DAC IC "AM6012PC" died and that he successfully replaced 2 of them with the modern type "Analog Devices DAC312". It is unknown if these generally suffer of ageing, but another e-mail confirmed that they tend to die. The 401 has the same part connected with its main voice CPU, while the direct successor Casiotone 403 already had the DAC hybrid "EXK-SIOL0025C" (12 pin SIL) - possibly to improve reliability.

The 401 is quite heavy (about 10kg?) because despite its case looks almost perfectly like wood, it is mainly made of plastic coated sheet steel. (Casiotone 201 and 202 were of genuine wood.) In spite of this it is not as robust as it appears, because at the corners of the side pieces (made of pressboard?) the plastic woodgrain tends to peel off. I had to hotglue mine back into place, but this sheet plastic stuff also cracks off easily when accidentally folded to hard. I bought my specimen in very dirty state; the whole case was severely sticky especially at the bottom. I am not sure whether it was fatty kitchen dirt or if anybody had tried to apply furniture wax on the case despite it is not of wood. I removed most of that gunk with a paper towel and vegetable oil (stay away from rubber parts) followed by water with dish washing soap, but it still feels sticky on hot days. The high quality speaker sits in an own thick plastic compartment of that even the cable hole was sealed with glue to turn it into a perfectly closed box. It is driven by a large hybrid amplifier module that is screwed to a sheet metal heatsink welded to the case bottom. This makes it very unpleasant to remove the mainboard because you have to unscrew the module and mess around with (possibly poisonous) old heat conductive paste. The dirty speaker grill had to be removed also for cleaning, because someone spilled cacao or similar on it.

Be careful with the 5 metal lashes with screw holes those hold the rear part of the control panel from inside. With case opened, these lashes are sharp as razor blades and easily damage the panel and PCB traces; with mine a preset sound LED failed by an accidentally cut trace after working on the opened keyboard. After soldering the trace I glued ribbon adhesive tape over the sheet metal lashes to make them less dangerous. After opening, a lot of broken small black rubber rings fell out of the case - likely they belonged under the piano keys somewhere for damping (keys feel a little loose), but turned brittle by oily room air or ozone. The quite complex analogue hardware of this instrument has the size of an old style PC mainboard and contains many discrete components for the analogue percussion. The percussion have individual trimmers for their decay time. The main IC numbers and sounds have some similarities with the smaller Casio MT-40. The power amplifier is a quite big hybrid module. Unusual is that the fingered chord is up to 12 note polyphonic with additional monophonic bass, while the main voice polyphony is only 8 notes.

I don't have a service manual of the 401, but got a photocopy of Casiotone 403, which was of great help to understand the general hardware architecture, because it has the same accompaniment hardware combined with the main voice section of Casio MT-60 (first 403 models had CPU version D776G with external bugfix circuitry). They are a good didactic example how Casio in early instruments made several different CPUs cooperate and combine their keyboard matrices rather than the centralized master-slave approach found in later hardware, and how despite almost self-contained CPUs often minor functions like clock rate conversion or preventing wrong key press order during preset sound selection used a crazy amount of "glue logics" ICs cluttering up the mainboard.

 

The microcontroller based bass accompaniment with tone generator is described in US patent 4561338. There it uses for each 2-bar bass pattern 16 ROM addresses (4 bit) with 5 bit bass note data (31=silence) and 5 bit percussion data (1 bit per sound). When during 2nd bar any chord key is pressed or held, the 4th address bit of the bass note counter resets and so repeats the 1st bar. The accompaniment CPU outputs a monophonic squarewave tone and trigger pulse for the analogue bass envelope circuit, and trigger outs for analogue percussion. In the actual instrument it also controls the chord tone generator TMS3615NS through an I/O IC.

 

Danger!: The IC TMS3615NS employs a +15V high supply voltage, which may destroy other ICs when accidentally shorted. Thus stay away from pin 4 and do not blindly poke around in the circuitry; also some logic ICs use this voltage.

Edited January 12, 2022 by CYBERYOGI =CO=Windler

[Jalbobble]

Hi,

I am new to this forum - hello!

I have just got my old Casiotone 403 out from the attic. It had a couple of knobs missing and the plug socket had come loose so I unscrewed it at the back and fixed the plug back in place. I'd been playing it for a few sessions fine but then heard a crack and it started smoking! I've obviously disconnected it from everything and darent switch it on again, although I noticed it still was 'on' despite the smoke when I turned it off.

I think I need a professional who knows what they are doing to have a look so I don't Burn my house down! Can anyone recommend a vintage casio repairer?

Thank you!

Jess

[CYBERYOGI =CO=Windler]

Likely a capacitor went up in soot. Typically electrolytics do that, but I read that in early Casios also foil caps in the primary (mains operated) side of power supply sometimes release their magic smoke. (See Badcaps website for general info.)

 

And always watch out to set the keyboard to the correct mains voltage (there is a black knob with slot a screwdriver, somedimes hidden under a lid). If voltage is set lower (e.g. 220 instead of 240V) the keyboard may sound normal but overheats voltage regulators and possibly amp parts.

[William Johnson]

Does anyone have a schematic drawing for the Casiotone CT-403?

[CYBERYOGI =CO=Windler]

I got a poor photocopy of the Casiotone 403 service manual but have no intact scanner.