Swapping parts off earlier boards

[griffin22]

Hi all,

I have managed to get hold of a donor board to try to fix up a faulty VA7 with a dead VDP1 issue. The board I got is a VA0 and the numbers on the chips are different. I was wondering if anyone knew could these be directly swapped or are the revisions different enough that I need to find identically numbered ICs?

Thanks for any help.

[zyrobs]

That's something I never tried. The pinouts are, as far as I know, the same. But there might be electrical differences, which makes it necessary to have some extra resistor or capacitor on certain pins, the lack of which would cause stability issues at best, burn out the chip at worst. The Megadrive had a bunch of hiccups like that between different versions of some chips.

To the best of my knowledge the VDP1 got two versions only, and the first one was only used on VA0 boards. But I've no clue on the difference. It could be a fix to a manufacturing defect that would make board construction simpler by not requiring a workaround in the form of extra resistors/caps. It could also be functionally 100% identical, being nothing more than a die shrink.

I wish we had scans of the service manuals for later board revisions, those would likely explain this since later boards can have different chips for certain ASICs even on the same board.

[griffin22]

Thanks for the response, I think I can get a VA9 donor board soon, so I will try to resurrect this VA0 board and grab the VDP1 off the VA9 once I have that. Would rather not risk killing a good chip.

Cheers