NMS8250 MSX 2+ Mod black screen

By ddehaan

Expert (73)

ddehaan さんの画像

12-02-2023, 10:00

Hi Everyone,

It seems that the modifications i'm making to the NMS8250 all fail somehow. After spending a long on getting the V9958 to work, i now have started to make the system a MSX 2+.

Bought a set om 3 roms from Bas Kornalijnslijper, read his documentation and watched his video. In the video tests the V9958 first, then the roms and then the LS chips.

The V9958 is working, but after the Rom mods i'm getting a black screen and that's it. Placed the old Roms back and desoldered the connection on the MY connector and everything works fine again.

So what could this be?

Faulty Roms? I've dumped the roms before making the modification, but i can't find them on the internet to verify if they are any good.

Wrong Connection? In the documentation there has to be a connection between the MY connector pin 38 and IC117, but in the video Bas said it should be Rom B (IC118). When i look at his work in the video i can see the wire is connected to IC117 so i guess it should be IC117.

I have done dozens of mods in the past, but i never had more trouble than with his MSX 2+ upgrade Sad

Is there anybody who can give me some ideas where to check?


By Daemos

Prophet (2170)

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12-02-2023, 15:00

If for example you are not planning to use the basic functions that make use of the smooth scrolling capabilities and screen modes of the V9958 you are in luck. Never had something not working on my V995ed MSX without the BIOS updates. You may consider just using the MSX with the V9958 if your are lucky enough not to need the MSX basic 3.0

By ddehaan

Expert (73)

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16-02-2023, 16:47

Bas was kind enough to send a new rom set and it turned out that the B rom was faulty. After reflashing the old B rom with the correct data it worked!

By mohai

Paragon (1031)

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16-02-2023, 19:25

I found an old thread where Bas explains how to do the upgrade.
Maybe you can see it more clear there.
Get the service manual from here, so you can be sure if you are doing something wrong.
I did a different mod to my 8280, I think I did not use any MY connector signal

By ddehaan

Expert (73)

ddehaan さんの画像

16-02-2023, 21:01

Thanks, but it's already working. As i explained one of the eproms (roms) was bad Wink