Gregory's Serverthen i add a few parts to the schematic, place a few footprints on the layout, and start hooking up wires. i'm starting with +5V and ground since those are easy.
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 one of the chips is a mystery chip -- it has been marked "862130" but that is not the real part number. the person who owns this board pulled the chip out and found this underneath! how rude... 😆 these are the pin connections i've deduced based on the rest of the board design. this chip seems to take over the Apple II's address lines and it copies sound samples over to the four DACs on the card. almost like a DMA controller. hmmmmmmmmmmm. 🤔 i've got it! it perfectly matches the pinout of the MC6844 DMA controller! mystery solved.     @tubetime you’ve heard of an op amp but what about a pop amp??? got some parts in from China, but I need to test them to see if they actually work. they've been painted and remarked (of course 😑) the ADC was tricky to test. one of them was bad and had some stuck outputs. I wonder if it'll work? I'll have to fire up the Apple II to find out.  @tubetime "Apple II goes here" ok, now I know you made it... I can guess its a super-rare IIe card that nobody has seen the likes of since the day after it came out...  @tubetime :-) Amazing. Before buying are you able to simulate the board, and is that useful? @benjohn there aren't any models of the larger chips. it's easier to just make the board and try it out irl!  @tubetime I used to have an old Xenix multi-user system that contained a *lot* of chips. Like a full megabyte of memory on a single board (12" square) with dozens of chips. Plus chips on the mainboard, chips supporting the system bus... |
so i just add a wire at a time to the schematic, propagate it to the layout, and make sure that it matches the existing traces. if there is any ambiguity, i just move on to the next trace. eventually i use a process of logical deduction to resolve that.