Scoping Casio SK-1
At CCRMA's Max Lab, I set up my Casio SK-1 for some digital oscilloscope probing.
#1 - I got a fresh Casio SK-1 from Ebay.
#2 - Taping wooden lifts onto the edges so that it can be flipped over without accidental key presses.
#3 - Removing the screws that hold the Bottom Case Subassembly on.
#4 - Scoping an envelope signal as it is asserted by the CPU. The black alligator clip is connected to ground (specifically, Pin No. 98, named”AGND,” which serves as the “Ground (0V) source for DAC (Digital to Analog Converter)”). The white alligator clip is connected to an Envelope Signal (Pin No. 89, named “EH,” the “Melody envelope signal output”).
You can see the schematic in the background - Google searching reveals that there are two versions of the Casio SK-1 Service Manual easily available. Both are pretty bad quality, which is a real problem if you want to look at the Main PCB Top and Bottom Views, or the Schematic Diagram. One version is either thresholded or has been processed in some way - it is usually (but not always) easier to read. I find myself struggling to find legible information, looking between the two versions of the PCB layout and Schematic Diagram, and recognizing sequential numbering schemes on repeated sub-circuits. For instance, there are four identical Pitch/Envelope Mixing Circuits, and their numbering schemes follow the same logic, so if one component name or value is illegible, it is possible to fill in the gaps by examining other sub-circuits.
Since keeping track of this is so tricky, I’m making some annotated overlays on photos I take of my own board. So far this has been very helpful. I’ll post them once they are more complete, hopefully they will prove useful to others.