He provided me pictures of these parts, they were two black custom ICs in SIL package.A 20 pin one marked 'HO755FE' with 'NH-0075' silkscreening on PCB and a 19 pin one marked 'HO745FD' but silkscreened as 'NH-0074' :
I was asked to do a reproduction of them and and that for this task two samples would have been sent to me to be analyzed.But, as I always do, I first looked for a bootleg board to see how the functions of these parts may have been reversed.Then I remembered I had somewhere a bootleg which was a perfect copy of the original except for the fact the 'NH-0075' and 'NH-0074' were not present as ICs neither in the form of replacement PCB but their functions were integrated on the board.I studied the hardware for a bit and could identify the equivalent circuits of the two custom ICs (highlighted in the picture below) :
I also figured out the functions, the 'NH-0075' is used to drive the inputs of both players (two custom ICs are present on PCB indeed, one for each player) while the 'NH-0074' is basically an RGB DAC.With this info in my possession I started my reproduction job.Being not complex circuits I quickly drawn schematics and came to a proper board layout for both :
Project files were sent to the manufacturer and boards received after some time.Here is how they looks populated with their parts :
The reproductions were sent for testing on hardware and after some time I received the news they were both working like the original custom ICs.John provided me some pictures as proof :
Thanks again to John from vintagevideogames.com for everything and long live to arcade!
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