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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.

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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.

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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.

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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.

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