VOGONS


First post, by eesz34

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I got this NOS AT case and motherboard, and the keyboard connector is not centered in the case hole. It's strange, I've never expected this would even be a thing.

From the case's perspective, the keyboard connector is too close to the expansion slots. The keyboard plug does fit into it without interference, barely. I don't have another AT case or MB so I can't compare. But because it's a big name MB, I'd wager my bets on the case being off.

Is there a mechanical drawing somewhere of AT form factor dimensions?

Reply 1 of 21, by eesz34

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eesz34 wrote on 2022-07-26, 15:44:

I got this NOS AT case and motherboard, and the keyboard connector is not centered in the case hole. It's strange, I've never expected this would even be a thing.

From the case's perspective, the keyboard connector is too close to the expansion slots. The keyboard plug does fit into it without interference, barely. I don't have another AT case or MB so I can't compare. But because it's a big name MB, I'd wager my bets on the case being off.

Is there a mechanical drawing somewhere of AT form factor dimensions?

Could someone maybe get out one of their AT motherboards and measure the distance from, say, the mounting hole at the corner where the keyboard connector is, to the center of the keyboard connector? I want to compare and determine if it's the case or MB that's off.

Inches or cm are welcome 🤣.

Reply 2 of 21, by TheMobRules

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On a random ASUS Socket 7 motherboard I have at hand I measured 23mm from the center of the mounting hole to the center of the keyboard connector. I made the measurement at the edge of the board.

Can you post pictures of the case you're having the problem with? Unfortunately this kind of annoyances are common with generic Baby AT cases. Not sure if there ever was an official spec for it, I think manufacturers just took the IBM AT as a reference for the positioning of mounting holes and connectors.

Reply 3 of 21, by jakethompson1

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TheMobRules wrote on 2022-07-26, 21:12:

On a random ASUS Socket 7 motherboard I have at hand I measured 23mm from the center of the mounting hole to the center of the keyboard connector. I made the measurement at the edge of the board.

Can you post pictures of the case you're having the problem with? Unfortunately this kind of annoyances are common with generic Baby AT cases. Not sure if there ever was an official spec for it, I think manufacturers just took the IBM AT as a reference for the positioning of mounting holes and connectors.

Supposedly the IBM XT 286 (5162) motherboard was the first Baby AT form factor and where it's derived from.

Reply 4 of 21, by eesz34

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TheMobRules wrote on 2022-07-26, 21:12:

On a random ASUS Socket 7 motherboard I have at hand I measured 23mm from the center of the mounting hole to the center of the keyboard connector. I made the measurement at the edge of the board.

Can you post pictures of the case you're having the problem with? Unfortunately this kind of annoyances are common with generic Baby AT cases. Not sure if there ever was an official spec for it, I think manufacturers just took the IBM AT as a reference for the positioning of mounting holes and connectors.

The MB is in the case with everything attached so getting a caliper or ruler in there is not possible, but I used some measuring instruments I have and got 24mm. So yeah I'd say the MB is correct and that makes sense I guess?

I'll do one better, here's the listing: https://www.ebay.com/itm/324957305191

You can easily see it's offset in the photos there. Otherwise it's a great case.

Reply 5 of 21, by TheMobRules

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jakethompson1 wrote on 2022-07-26, 21:25:

Supposedly the IBM XT 286 (5162) motherboard was the first Baby AT form factor and where it's derived from.

Right! I think the only difference is that some of the mounting hole positions are taken from the original AT boards (though in some cases boards have holes that match both XT and AT).

eesz34 wrote on 2022-07-26, 21:44:

I'll do one better, here's the listing: https://www.ebay.com/itm/324957305191

You can easily see it's offset in the photos there. Otherwise it's a great case.

Does the case have a removable motherboard tray? In that case you can maybe tweak it so that the keyboard connector is centered on the hole. Or you can loosen some of the screws that attach the motherboard to the tray and try to reposition it, usually the nylon standoffs allow for some wiggling. Also check if the expansion cards are straight and sit properly on the slots, that can give you an indication of whether the board is in the correct position.

Reply 6 of 21, by kaputnik

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eesz34 wrote on 2022-07-26, 20:58:
eesz34 wrote on 2022-07-26, 15:44:

I got this NOS AT case and motherboard, and the keyboard connector is not centered in the case hole. It's strange, I've never expected this would even be a thing.

From the case's perspective, the keyboard connector is too close to the expansion slots. The keyboard plug does fit into it without interference, barely. I don't have another AT case or MB so I can't compare. But because it's a big name MB, I'd wager my bets on the case being off.

Is there a mechanical drawing somewhere of AT form factor dimensions?

Could someone maybe get out one of their AT motherboards and measure the distance from, say, the mounting hole at the corner where the keyboard connector is, to the center of the keyboard connector? I want to compare and determine if it's the case or MB that's off.

Inches or cm are welcome 🤣.

It's harder than it might seem to do this measurement with any precision using a sliding caliper, so take this with a grain of salt. Got 31.8 mm from edge to the center of the connector.

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Measuring mobo edge - connector edge (42.5 mm), and subtracting half the connector's measured width (20.8 / 2 = 10.4) gives 32.1 mm. This is a better measurement method, but it's assuming that the connector is symmetrical over its center.

Edit: distance from edge to mounting hole center is 8.0 mm, subtract that from the earlier measurements if you rather want mounting hole - connector c/c.

Last edited by kaputnik on 2022-07-29, 08:08. Edited 2 times in total.

Reply 7 of 21, by eesz34

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TheMobRules wrote on 2022-07-26, 22:12:
Right! I think the only difference is that some of the mounting hole positions are taken from the original AT boards (though in […]
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jakethompson1 wrote on 2022-07-26, 21:25:

Supposedly the IBM XT 286 (5162) motherboard was the first Baby AT form factor and where it's derived from.

Right! I think the only difference is that some of the mounting hole positions are taken from the original AT boards (though in some cases boards have holes that match both XT and AT).

eesz34 wrote on 2022-07-26, 21:44:

I'll do one better, here's the listing: https://www.ebay.com/itm/324957305191

You can easily see it's offset in the photos there. Otherwise it's a great case.

Does the case have a removable motherboard tray? In that case you can maybe tweak it so that the keyboard connector is centered on the hole. Or you can loosen some of the screws that attach the motherboard to the tray and try to reposition it, usually the nylon standoffs allow for some wiggling. Also check if the expansion cards are straight and sit properly on the slots, that can give you an indication of whether the board is in the correct position.

No tray, no. And interestingly, the 3 cards in there seem to line up perfectly.

It's just odd that someone would manufacture a case with something like that so noticeably off center.

Reply 8 of 21, by eesz34

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kaputnik wrote on 2022-07-26, 22:23:
It's harder than it might seem to do this measurement with any precision using a sliding caliper, so take this with a grain of s […]
Show full quote
eesz34 wrote on 2022-07-26, 20:58:
eesz34 wrote on 2022-07-26, 15:44:

I got this NOS AT case and motherboard, and the keyboard connector is not centered in the case hole. It's strange, I've never expected this would even be a thing.

From the case's perspective, the keyboard connector is too close to the expansion slots. The keyboard plug does fit into it without interference, barely. I don't have another AT case or MB so I can't compare. But because it's a big name MB, I'd wager my bets on the case being off.

Is there a mechanical drawing somewhere of AT form factor dimensions?

Could someone maybe get out one of their AT motherboards and measure the distance from, say, the mounting hole at the corner where the keyboard connector is, to the center of the keyboard connector? I want to compare and determine if it's the case or MB that's off.

Inches or cm are welcome 🤣.

It's harder than it might seem to do this measurement with any precision using a sliding caliper, so take this with a grain of salt. Got 31.8 mm from edge to the center of the connector.

DSC_6938.JPG

Measuring mobo edge - connector edge (42.5 mm), and subtracting half the connector's measured width (20.8 / 2 = 10.4) gives 32.1 mm. This is a better measurement method, but it's assuming that the connector is symmetrical over its center.

I think the only issue with this is you're measuring from the MB edge rather than referencing it to a hard attachment point. I don't know if AT MBs are supposed to be a specific size with reference to the screw hole.

Reply 9 of 21, by kaputnik

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eesz34 wrote on 2022-07-26, 22:32:
kaputnik wrote on 2022-07-26, 22:23:
It's harder than it might seem to do this measurement with any precision using a sliding caliper, so take this with a grain of s […]
Show full quote
eesz34 wrote on 2022-07-26, 20:58:

Could someone maybe get out one of their AT motherboards and measure the distance from, say, the mounting hole at the corner where the keyboard connector is, to the center of the keyboard connector? I want to compare and determine if it's the case or MB that's off.

Inches or cm are welcome 🤣.

It's harder than it might seem to do this measurement with any precision using a sliding caliper, so take this with a grain of salt. Got 31.8 mm from edge to the center of the connector.

DSC_6938.JPG

Measuring mobo edge - connector edge (42.5 mm), and subtracting half the connector's measured width (20.8 / 2 = 10.4) gives 32.1 mm. This is a better measurement method, but it's assuming that the connector is symmetrical over its center.

I think the only issue with this is you're measuring from the MB edge rather than referencing it to a hard attachment point. I don't know if AT MBs are supposed to be a specific size with reference to the screw hole.

Yeah, that hit me too, edited the post 😀

Reply 10 of 21, by eesz34

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kaputnik wrote on 2022-07-26, 22:37:
eesz34 wrote on 2022-07-26, 22:32:
kaputnik wrote on 2022-07-26, 22:23:

It's harder than it might seem to do this measurement with any precision using a sliding caliper, so take this with a grain of salt. Got 31.8 mm from edge to the center of the connector.

DSC_6938.JPG

Measuring mobo edge - connector edge (42.5 mm), and subtracting half the connector's measured width (20.8 / 2 = 10.4) gives 32.1 mm. This is a better measurement method, but it's assuming that the connector is symmetrical over its center.

I think the only issue with this is you're measuring from the MB edge rather than referencing it to a hard attachment point. I don't know if AT MBs are supposed to be a specific size with reference to the screw hole.

Yeah, that hit me too, edited the post 😀

Well your measurement more or less matches my MB, and also TheMobRules. So someone couldn't get the case hole into the right position, which is kind of strange.

Reply 11 of 21, by eesz34

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Just found an interesting picture, probably not interesting to many of you experts out there. But this pic shows a keyboard hole in a no-name type case that's oblong, so apparently there were issues with this.

https://ancientelectronics.files.wordpress.co … /04/386alt2.jpg

Come to think of it, I think I've seen this type of thing somewhere before, back in the day when AT form factor was current.

Reply 12 of 21, by Horun

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I cannot find it now but somewhere in my docs archive is a PDF that gives the actual AT and Baby AT case specs.
AFAIRRC: AT and Baby AT used same mount to KB spacing but not from the left edge (as the OP asks) but from the KB to mount first mount to right, behind most ISA slots and then on to the far right end of board.
Many Baby AT have a "slot" for the far right mount (looking at baord from back) so it can be used in various older full AT cases which had some variants based on the original IBM AT board..
With advent of Baby AT they also added more mounts to the shorter board. If you ever see an old full AT tower it will have movable mounts so it can use either full AT or Baby AT boards.

Ok for comparison: checked my full AT sized DTK PEM3301 versus a typical 486 baby AT. Biostar and PcChips
From center KB to first mount toward ISA is: 1 - 15/16" for full AT, same with a Biostar 1433/50 and a Amptron 9700
Next measure from center KB to far right hole (again looking from back of board): full AT = 6-13/16", Biostar and Amptron = 6-11/16" and 6-13/16" depending on center of the "slotted" type mount hole.
You cannot use the mount hole left of the KB as a measure, that is not how thee standards were developed....AFAIK 😁

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.

Reply 14 of 21, by Errius

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Yes, the specifications appear to have been fairly loose. I've had great difficulty getting certain AT motherboards into supposed AT cases. Also, certain ISA cards won't fit in certain AT cases/boards - you have to remove the I/O bracket to use them, because the alignments are all wrong.

“I like to dissect PCs. Don't you know I'm utterly insane?"

Reply 16 of 21, by eesz34

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pete8475 wrote on 2022-07-27, 19:14:

I have that case and it lines up with the motherboard I have in it.

K6-2+ 450, Asus VX97 Build - updated now to include some 430TX vs. 430VX benchmarks

Could you measure something on it so I can compare? A good one might be distance from the closest edge of the closest slot to the closest point on the keyboard hole. See picture for description and my measurement.

For what it's worth I used a caliper around those edges, but the keyboard port misalignment on this is more than just rounding error. Luckily the slots seem to line up perfectly.

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Reply 17 of 21, by eesz34

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Errius wrote on 2022-07-27, 19:03:

Yes, the specifications appear to have been fairly loose. I've had great difficulty getting certain AT motherboards into supposed AT cases. Also, certain ISA cards won't fit in certain AT cases/boards - you have to remove the I/O bracket to use them, because the alignments are all wrong.

I had this problem putting an ISA NIC into a Compaq. I took the bracket off and made the bracket holes oblong and that fixed it, so that wasn't bad.

I guess that's the price we paid for cheap clones.

Reply 18 of 21, by pete8475

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eesz34 wrote on 2022-07-28, 15:46:

Could you measure something on it so I can compare? A good one might be distance from the closest edge of the closest slot to the closest point on the keyboard hole. See picture for description and my measurement.

For what it's worth I used a caliper around those edges, but the keyboard port misalignment on this is more than just rounding error. Luckily the slots seem to line up perfectly.

Sure, give me a minute and I’ll measure it. Your video card looks like it’s mounted weird btw.

EDIT - Pics. I don't have a caliper so I used a measuring tape. To me it looks like 59 or 60mm. Also see how the video card is nice and straight in the expansion slot? Something is weird on your end.

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Reply 19 of 21, by eesz34

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pete8475 wrote on 2022-07-29, 03:10:
eesz34 wrote on 2022-07-28, 15:46:

Could you measure something on it so I can compare? A good one might be distance from the closest edge of the closest slot to the closest point on the keyboard hole. See picture for description and my measurement.

For what it's worth I used a caliper around those edges, but the keyboard port misalignment on this is more than just rounding error. Luckily the slots seem to line up perfectly.

Sure, give me a minute and I’ll measure it. Your video card looks like it’s mounted weird btw.

EDIT - Pics. I don't have a caliper so I used a measuring tape. To me it looks like 59 or 60mm. Also see how the video card is nice and straight in the expansion slot? Something is weird on your end.

Thank you so much. Good to know it isn't because mine is screwy.

And yes, I did notice something with the video card when I took these pictures but couldn't immediately determine what it was. It went in easy as did the other two boards in there. And looking at the uncropped picture, the NIC two slots down is straight as an arrow.

But I see your keyboard port is offset just like mine? That's the main issue. The NMB I had plugged into it worked out just fine though and barely cleared the cutout.