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Sega ST-V ModBios issue

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Kataklysm

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Hi there!

I've recently ordered a Modbios from Ebay and as I wanted to swap the originial, came across the following issue: The EPROM sent to me has 42 pins instead of 40.

Does anyone have any experience regarding this? Should I leave the 2 extra pins hanging or...?

Thanks in advance.

bios.jpeg
 
Gross... if 2 pins are to be hanging its the other 2.

27c400s are expensive, I'm wondering if they used a 27c800 instead. I would press them on why they used the wrong chip. This kind of shortcut (doubling the rom to a physically larger chip with more pins) is passable in your own work, but people shouldn't be selling it like this IMHO.
 
Last edited:
skate323k137 said:
Gross... if 2 pins are to be hanging its the other 2.

27c400s are expensive, I'm wondering if they used a 27c800 instead. I would press them on why they used the wrong chip. This kind of shortcut (doubling the rom to a physically larger chip with more pins) is passable in your own work, but people shouldn't be selling it like this IMHO.
Click to expand...

I've managed to reach the seller, he replied the same: pins 1 and 42 should be left hanging.. Being honest it is a bit strange, since on the Ebay display photo he has a 40 pin EPROM.

@Darksoft I bought the board with a burned 40 pin EPROM which had either the EU or the US bios, so I guess if I leave 1 and 42 out, it should be ok.
 
Kataklysm said:
I've managed to reach the seller, he replied the same: pins 1 and 42 should be left hanging.. Being honest it is a bit strange, since on the Ebay display photo he has a 40 pin EPROM.

@Darksoft I bought the board with a burned 40 pin EPROM which had either the EU or the US bios, so I guess if I leave 1 and 42 out, it should be ok.
Click to expand...
Technically if the rom is doubled it will probably work, if the board has the roght pinout, but ideally the highest address line should be pulled high or low for stability.

On a 27C800 pin 42 is not used. Pin 1 could be grounded to keep the ROM in the lower bank.

However! 27c400 and 27c800 are MASK equivalent. If your board had an official Sega EPROM with a window, you need a 27c4002 / 27c4096. This rom probably won't boot.
 
Kataklysm said:
I guess I got lucky, the board boots and all the games are working fine. Thanks for the help :)
Click to expand...
No problem.

I will admit, I have used this solution in a pinch, but it's unfortunate to see people charging for it. Anyway, all is well that ends well it seems, happy gaming :)
 
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