Audio Circuit (PC Engine GT)
Basic notes taken during some diagnostics, dumped here for quick reference until I make more format docs.
Audio IC100 pinout
Pin 1 * Output A Speaker Pin 2 5V Pin 3 Output B Headphone Pin 4 GND Pin 5 Input B- Headphone Pin 6 Input B+ Headphone (Pin 3 of vol wheel) Pin 7 Input A+ Speaker (Pin 4 of vol wheel) Pin 8 Input A- Speaker
Basic visual of the circuit path from pin 1, through capacitor, splitting off to resistor and inductor.
CC103 is opposite side of amp R109 is just above pin 1 of amp L100 is to left of R109
Audio amp is NJM2073M, labelled U10 near volume wheel Pin 1 is top left, then going anti-clockwise so top right is pin 8.
Output A is sent to the pin 11 of bottom right white connector (speaker +) but not directly, through some switch that gets disconnected when headphones are inserted. To test if that part of circuit (the logic to disconnect/connect speaker) is broken, just send a wire directly from pin 1 of the U10 amp to pin 11 of the connector and see if you get audio. The speaker will never turn off when headphones are inserted but proves if the U10 audio amp is working.
Headphone connector middle pin next to L103 silkscreen closest to letter L is grounded when no headphones, disconnected from ground when headphones inserted
Connector for white ribbon going to front board containing speaker.
Pin 12 Speaker - (Ground from motherboard side) Pin 11 Speaker + Pin 10 Ground Pin 9 ASIC Interface BUS Pin 8 ASIC Interface BUS Pin 7 ASIC Interface BUS Pin 6 ASIC Interface BUS Pin 5 ASIC Interface BUS Pin 4 ASIC Interface BUS Pin 3 ASIC Interface BUS Pin 2 ASIC Interface BUS Pin 1 Presumably switched ground of some kind or switch power
Vol when pins top to bottom
Pin 1 Pin 2 Pin 3 Input B+ (Pin 6 of amp) ------| 5K Pin 4 Input A+ (Pin 7 of amp) ------| Pin 5 GND
Headphone connector on front board bottom center pin is ground, the two pins above it get grounded when headphones inserted. Those 2 pins go to the BU5782K IC. This IC handles controller signals and link cable communication as well has headphone insert signal to disable output A of audio amp when headphones inserted.