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Thread: Help with power requirements for Olivetti 286 motherboard

  1. #1
    Join Date
    Apr 2020
    Location
    Belfast, Northern Ireland
    Posts
    10

    Default Help with power requirements for Olivetti 286 motherboard

    I've been gifted an Olivetti M203 motherboard which I'm fairly sure is from a model M290S computer. I have no idea if this works or not but I want to try and power it on just on the chance it does. Problem though is that these Olivetti's all used proprietary power supplies and this one uses a 10pin connector. I've managed to bell out 9 of the pins using the ISA riser for reference and I've figured out +5v, +5v, ground, ground, ground, ground, +12v, -12v, -5v. The last pin though has me stumped. It only seems to be connected to some 74 logic and a custom olivetti IC. Its connected to the logic not the ground or VCC pins so I've no idea what this is doing, any suggestions?

    Is it possibly some sort of reset line or power good signal or maybe something to isolate the monitor pass through (this is a feature on my Olivetti 386 all be it, its contained within the PSU).

    If I hook everything else up to a do you think it would work without this pin? I suppose there's one way to know but before I go trying I thought I'd ask.

    There is also another potential issue... when belling out the various pins I noticed a reading of 167ohms between +5V and the chassis ground which changes to about 200ohms between the +5V and ground pins (at the psu connector but also at components around the board). Surely this can't be correct?

  2. #2
    Join Date
    Apr 2020
    Location
    Belfast, Northern Ireland
    Posts
    10

    Default

    Well I figured it out. Took a chance that Olivetti would just have reworked the AT standard rather than reinvent it so the last pin had to be power good.

    The board posted much to my surprise all be not ever time. On first power up it'll through a timer error on screen but quickly resetting the PSU will make it boot properly.

    Unfortunately I can't get it to boot a disk yet and it seems to be in a 40 column mode rather than 80 column as the BIOS reports. My thoughts now are since the battery is removed any settings in the bios even after a soft reset are not being stored. I have a new battery on order, hopefully that'll fix the issue.

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