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IBM PS/2 mca raid adaptor problems

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First post, by Grain

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I recently got a PC server 500 with a pentium 90, 32mb and 7 8gb SCSI drives, the machine had a raid and non raid model. Using the “cheetah” card, I’m having problems of the bios often believes that the card is a second motherboard. Saying Slot 1 - built in features, and lists most of the same configurable stuff as the main board but with some stuff being wrong such as a music note for if there’s a co processor and how much ram is install.

Upon removing the card the system doesn’t give any errors or anything, apart from a 165 saying I’ve removed a card, and after a auto configure it’s fine, but once I put the card back in rarely it shows the cards bios and says starting drives but giving a 165, and rebooting the machine or auto configuring it will make it think it’s the main board.

I’ve tried leaving the system without a cmos and power for hours without any change and I’ve even tried removing the Dallas 1225Y which I assume holds the array information, which is still working as when I first got the machine I was able to use it for a bit and configured 2 logical drives, and when it rarely shows the cards bios it does say it knows about my two logical drives.

So if I found a replacement for the Dallas chip would I have to copy over any of the data? (I don’t mind loosing the array info) and if anyone’s had any card playup like this before.

Reply 1 of 3, by luckybob

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the battery in the dallas chip should be dead by now. I'd do the battery mod. its all over youtube. you are losing settings and its causing issues. If you arent comfortable with doing the mod yourself, there should be plenty of resources on epay for turn-key modules.

just be sure to buy the ones specifically compatible with what you have. IBM is NOT known for user friendly repair.

It is a mistake to think you can solve any major problems just with potatoes.

Reply 2 of 3, by Horun

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This was brought up back in about 2020 about a 1225Y, the only replacement for a Dallas/Maxim 1225Y is an ST m48z18-100pc1 (and available) AFAIK. Easiest way IMHO.
The internal battery is not easy to access so would take some diff mod than other Dallas types. Unlike 1287/12887/etc there are no missing pins to identify where to dremel so connecting an external battery is more difficult and dangerous.
One way to mod would be inserting a very low Vdrop diode in the PSU VCC path next to pin 28 and adding a 5v source (like non rechargeable battery with another low Vdrop diode) direct to that 1225y vcc pin 28 .
And the battery ground attached to the ground near the 1225y.

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 3 of 3, by Grain

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Horun wrote on 2025-02-22, 05:05:
This was brought up back in about 2020 about a 1225Y, the only replacement for a Dallas/Maxim 1225Y is an ST m48z18-100pc1 (and […]
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This was brought up back in about 2020 about a 1225Y, the only replacement for a Dallas/Maxim 1225Y is an ST m48z18-100pc1 (and available) AFAIK. Easiest way IMHO.
The internal battery is not easy to access so would take some diff mod than other Dallas types. Unlike 1287/12887/etc there are no missing pins to identify where to dremel so connecting an external battery is more difficult and dangerous.
One way to mod would be inserting a very low Vdrop diode in the PSU VCC path next to pin 28 and adding a 5v source (like non rechargeable battery with another low Vdrop diode) direct to that 1225y vcc pin 28 .
And the battery ground attached to the ground near the 1225y.

It's not an issue with the battery as moving it to a different slot makes it work for a while, and when it does it remembers it's config (what the dallas chip stores)

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