Reply 20 of 24, by Jepael
Yes sometimes a digital inverter can be used for analog signals too.
Good news is that I was able to figure out the connections of the digital parts (bus address decoding, buffering, clock divider, etc) and the connections match my expectations. Chip select decoded from address bus with the two 138s go directly to OPL2 -CS and 245 -OE. Doubly inverted (buffered) -IOWR goes directly to OPL2 -WR and doubly inverted (buffered) -IORD goes to both OPL2 -RD and 245 DIR. Address pin A0 goes directly to OPL2 A0.
Bad news is that it is extremely hard to see how the analog parts are connected together, as I can't see the PCB wires under the chips and other components. The surroundings of the operational amplifier (U8) is most unclear, as well as some of the output amplifier connections (U9), including the volume control knob and the output mute parts (Q1).
If I had a card on my hands, I would measure what is connected to where with a multimeter by using the continuity test beep mode. So anyone with a Adlib, multimeter and basic electronics skills can help me fill out the blanks.