I am unfortunately not in game collecting anymore. (I wish I had kept some of my boards....)

However, the information below will be very interesting for many other collectors.

Everything below has been built and tested. The Nintendo color inverter is probably the best one you can find. I built others and this one is the easiest and produces the best results.
Sinistar speech board schematics
Sinistar speech board (bottom layout)
Sinistar speech board (top layout)
Sinistar speech board (top overlay)
Sinistar speech board (check plot)
Nintendo color inverter (bottom layout)
Nintendo color inverter (check plot)
Color inverter with built-in amplifier (top overlay)
Color inverter with built-in amplifier (bottom layer)
Color inverter with built-in amplifier (check plot)
Galaga small board (bootleg blue set) (bottom layer)
Galaga small board (bootleg blue set) (top layer)
Galaga small board (bootleg blue set) (top overlay)
Galaga small board (bootleg blue set) (check plot)