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Thread: at motherboards in atx cases

  1. #1
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    Default at motherboards in atx cases

    Just checking for future use. It seems harder & harder to find AT cases that aren't insanely expensive.

    I have a 2 part question: can you match up an ISA motherboard with ATX case slots, and are there differences in the standoffs?

    I know the power supplies are different, and that adapters are common & inexpensive as long as you don't have a -5v sound card.

  2. #2
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    Most AT style motherboards will line up with slots on the back of the case, the problem is the standoffs. You'll probably have to end up marking, drilling and tapping more mounting holes for large and very small AT boards. Using plastic standoffs is an option if you aren't using more than a couple, else the board won't be secured properly and can end up sliding around or flexing, causing potential damage to the motherboard.

    As for the -5v rail, you'll want to either get a supply that has it, or make it with a negative voltage regulator. Many motherboards check for the presence of the -5v rail and won't POST if it is missing.

  3. #3
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    Funny, I'm planning to do the opposite; modern hardware in an old case :P

    I measured the width and spacing of the ISA slots on my 5170 and two other AT clones, and compared it with ATX cases from the 90s, 2000s, and 2010s. They all come to approximately 8-9mm wide and 11-12mm spaced apart. So you're good there.
    Also, when considering an ATX case, choose one where you can remove the I/O shield. It'll leave a gaping hole but allows access to the keyboard port. Skilled hands could fabricate a custom shield from sheet metal.
    And choose an ATX PSU with a on/off switch on the rear, I don't think the momentary switch on the case can be used.

    I cannot think of any other conflicts between the two. Let us know how your build goes!

  4. #4
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    Quote Originally Posted by Casey View Post
    can you match up an ISA motherboard with ATX case slots, and are there differences in the standoffs?
    I have a 486 in an ATX myself, works just fine and everything lines up,n the only gotcha's are:

    1. The IO shield - You can just leave it out completely, or if you are lucky there are some ATX io shields that have the AT keyboard hole in the right place (I was lucky enough to find one), you could probably easily make one if you found an IO cover that had no holes in it.

    2. The power switch on the front of the case. ATX power switches are momentary and low voltage, AT on the other hand are on/off toggles that toggle the 120V high voltage. In my case I used an ATX power supply, lopped off the ATX motherboard connector and replaced it with AT molex connectors. I then found a replacement switch for the power button that was a toggle switch and use it to bridge the power on wire with a ground wire. Works perfectly.

    Quote Originally Posted by Casey View Post
    I know the power supplies are different, and that adapters are common & inexpensive as long as you don't have a -5v sound card.
    First off, -5V is part of the older ATX spec, so there are some ATX power supplies out there that have a -5V rail, not many though. But there are also adapter cables that adapte ATX to AT and include a -5V regulator, so can be used to make any ATX PSU into an AT PSU with -5V. Look them up on ebay, IIRC they ae not super expensive.

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  5. #5

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    I have a whole tote full of old ATX supplies with -5V. They aren't hard to find at all

  6. #6
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    I've got an either/or case marketed fairly early in the ATX introduction. It uses different I/O plates, which are screwed in, so a regular AT I/O shield doesn't work.

  7. #7

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    I have a case like that as well, but it will accept snap-in IO shields in addition to the screw in ones it was designed for.

    There are 3d print designs for snap in shields that fit an AT style full-DIN keyboard connector on thingyverse. They also have punch outs for DE-9 and DB-25 connectors as well as a miniDIN ps/2 mouse.

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    Quote Originally Posted by lutiana View Post

    1. The IO shield - You can just leave it out completely, or if you are lucky there are some ATX io shields that have the AT keyboard hole in the right place (I was lucky enough to find one), you could probably easily make one if you found an IO cover that had no holes in it.
    Early last year I took a flyer on 2 'blank' shields form you know where. I only paid about $3 total and I completely forgot about them until they arrived about 3 months or so later. I was going to use them on an AT board cobbled into an ATX case. To tell the truth, that project never got off the ground and right now, I can't remember what the heck I was thinking anyway as my Intel 486 DX2/66 is up and running nicely in a mini AT tower. Bottom line is you can find those blank shields only you need to be handy with the fab.
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  9. #9
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    So it sounds like stand offs would be the biggest challenge.

    The AT/ATX power adapters I've seen for sale all seem to include a "hard" power switch.

    A few years ago I ran across on eBay i/o blanks with just an AT connector hole. Can't find them now. Have seen several blank shields for sale, including mesh types you apparently cut out the desired holes.

    Am currently shopping for a 486 motherboard to fill out my collection. Would cheerfully kill for a Deskpro386 (the original Darth Vader style, not the later consumer version) but at least I have a Zenith 386 16Mz system. Have several 8088, 286, and portable systems to cover the pre-Pentium era. It seems once we hit the Pentium era consumer systems were all over the place. I prefer white box systems. That's the problem with both Compaq & Zenith; they both feature proprietary cases & power supplies in case you need to replace something.

  10. #10
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    Quote Originally Posted by maxtherabbit View Post
    I have a case like that as well, but it will accept snap-in IO shields in addition to the screw in ones it was designed for.

    There are 3d print designs for snap in shields that fit an AT style full-DIN keyboard connector on thingyverse. They also have punch outs for DE-9 and DB-25 connectors as well as a miniDIN ps/2 mouse.
    My problems mostly are with non-standard cases that don't take snap-in I/O shields. I've resorted there to fabricating them out of single-sided PCB stock. They work and don't look awful.

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