@darry Thanks for the info. I am not sure if I can fully disable it with the jumpers on the board unlike the VGA (which holds the reset line to the chip high). I just used my soldering iron to melt the case of the Dallas chip to get to the pins I needed. Also at some point managed to plug it in backwards and blow it up so I had to order some replacement ones as well.

Poot36 wrote on 2022-07-02, 22:48:

@darry Thanks for the info. I am not sure if I can fully disable it with the jumpers on the board unlike the VGA (which holds the reset line to the chip high). I just used my soldering iron to melt the case of the Dallas chip to get to the pins I needed. Also at some point managed to plug it in backwards and blow it up so I had to order some replacement ones as well.

If you meant disabling the CMD640, there is always the option of cutting off its DC power supply or heat-gunning it off the board permanently (not sure if either of these options would be sane or even likely to be effective/without caveats). Beyond what is known officially, there is likely a backstory that explains how a chip like the CMD640 with so many flaws made it into so many designs (including high profile ones) without nobody either discovering said flaws before products hit shelves, or worse, knowing about said flaws, but going ahead with it anyway .

EDIT : https://www.mindprod.com/jgloss/eideflaw.html for more details and backstory

Thanks for the idea for the Dallas. I might try that instead of the Dremel .

@darry If you do try the soldering iron approach make sure to wipe the plastic off the tip as quickly as possible to avoid damaging the plating on the tip. Also have good ventilation as well. And be careful not to leave solder balls stuck in the melted plastic on the chip if possible to prevent them from pinging off in the future and potentially shorting something out on the motherboard. I will see if there is a easy way to hold the CMD640's reset line in reset so it does not show on the PCI bus.

This thread is missing a term: PISA

The brown slot is physically identical to ISA, but there the similarities end. A slot like this used to supply PCI and ISA risers is referred to as a PISA slot. The risers that don't work are 'regular' PISA; apparently AST did something less regular in this particular system. Given the great work in here finding that pinout and modding a riser, it would be a shame if someone searching for AST PISA didn't find it. Now they hopefully can 😀

@dionb It looks like a EISA slot that has been used for both ISA and PCI. I think the amount of pins are the same.