I can't speak for OEM specific cases like IBM/Compaq/Packard Bell/etc because they all had their own little quirks and proprietary nuscinces.

But as far as regular old AT Cases go? I'd say their no harder or easier to work in then your modern ATX/Micro ATX case.

Sharp edges are just a fact of life with cases from this era. Some may have minor differences like requiring you to takeout the motherboard tray to fully access all the drive bays (that's how mine works), and -some- will have screwholes for special AT PSU designs (so no ATX will fit. Allways check the back of the case just incase) but otherwise it's fairly straightforward.

Most AT Cases have regular old front panel connectors like you find these days. Only the front power switch is usually wired to the PSU.

AT PSUs? Well IMO, Preferably use a ATX-AT converter for safety and peace of mind. Unless you can recap your AT unit. Just remember to match the cables black wire-to-black wire and you won't get your board killed.

I have a dumb little rhyme to help me remember.
"Black to black or there's no going back".

...but sometimes forgetting happens to even the best of us 😁

Depends. a long time ago AT cases didn't have standoffs they had these plastic retention clips like the ones that they attach heatsinks with that you would put in the motherboard holes. And then you would slide the board into the motherboard tray and those things would hold the board on there. Except a lot of times you couldn't insert VLB cards in the slots because of board flex with that old mounting system so you had to insert cards before u put the board in.

I wouldn't attempt a 5170 as the power supply is likely not enough wattage and may not have "modern" connectors like for 3 1/2" floppy drive, etc.
It is true you can connect AT power backward. The rule is black wires next to each other.
As you point out, a late model "AT" power supply (technically LPX) is "hard" power - that is, a power switch in the front of the case has a black cable going to it with 120V running inside. Most power supplies used a switch like this https://sep.yimg.com/ca/I/cablesonline_2268_82431278 that just screws into a designated place on the front of the case. Other cases used something custom like a 1/0 rocker switch. Back then it was common for a case to come with a power supply included bypassing that issue entirely.
I don't see why you would need to open up the power supply. You might have to disconnect and reconnect wires if you need to change the power switch, though.

I will point out though - I have built several reverse-stealth machines. It has been straightforward to put a Baby AT motherboard into a modern ATX case. You know it will fit so long as the motherboard is just wide enough for VLB slots and no bigger. On one system, I used a StarTech AT power supply (since discontinued) and adapted the case to remove the tiny ATX power switch and put the "big" AT power switch in its place. On another system I just finished, I used an ATX power supply and an ATX to AT converter. The only issue with these is that the power switch in an ATX case is momentary - the circuit is only closed when you hold it down; an ATX-AT converter needs it to stay closed until you want to shut off the machine. I replaced the power switch with an E-Switch TL2285EE which fit in my case, and is a different design that latches on until you press it again.

There are three other minor issues. You either need to find an I/O shield with a hole for the keyboard port, or drill one. I also have an "official" AT I/O shield from a company in Florida that I haven't been able to get ahold of to order more (possibly coronavirus). The other issue is that ATX cases have 7 slots rather than 8, so you lose access to one slot. My HOT-591P doesn't even have an 8th slot so that's a non-issue; for a 486 you'll just want to make sure the slot closest to the keyboard port is not a VLB slot since you only have a few of them to start with. Finally, ATX cases of course have front ports useless for a 486. I used to use the (since discontinued) Thermaltake V3 that had these conveniently located just over a 3.5" drive bay, so you could just saw them away and put the floppy drive in its place. My last one was a Cooler Master RC-350 with the same design, but unfortunately there are extra plastic parts in the way of putting a drive in. I'm thinking of getting a thin black piece of plastic that will pass as an empty drive bay cover and just gluing it over those ports.

🤣 I was about to say that if building a AT system do not use an OEM case, too many problems could occur.

Horun wrote on 2020-07-31, 02:08:

🤣 I was about to say that if building a AT system do not use an OEM case, too many problems could occur.

Yeah, that is a good point. By the 486 timeframe AT motherboards were only used by white-box manufacturers and people who built their own machines. So you were actually better off buying a no-name prebuilt machine vs. brand-name as that meant it was more likely they used standard AT parts that you as an individual would have bought, rather than custom-fit. The downside of an AT motherboard is that the only external port is the keyboard, and of course that it's AT instead of PS/2. Any built-in ports like PS/2 mouse, serial and parallel have to have little ribbon cables in order to connect to the proper port on the back of the case. The Packard Bells, HPs, Dells, etc. of the world used LPX, which has all the ports on the back of the motherboard, kind of like ATX, but unfortunately with every motherboard needing a custom-fit case with the proper holes. There weren't I/O shields yet. The other part of LPX is that the ISA slots could be horizontal rather than vertical (in a desktop case); this required a riser card that plugged into the motherboard such that the add-on cards would be parallel to the motherboard. The reason for doing this, like a rackmounted server case today, is so that a desktop case could be shorter than the standard height of an expansion card.

working with AT cases isn't the problem, it's FINDING them for less than $100

maxtherabbit wrote on 2020-07-31, 03:57:

working with AT cases isn't the problem, it's FINDING them for less than $100

And this is why I snatch up every cheap AT case or system I find... I probably have enough now though.

And really, you can use an ATX case anyway and just need a rear I/O plate with just the KB hole.

Power supply and case are the easy part. Hard part is when you don't have the manual and/or couldn't figure out the millions of jumpers on the board, and scratching your head for months. 😁

I recently dug my old IBM ValuePoint out of storage to play with but the motherboard has started intermittently failing to POST so I decided to replace it. No luck finding the same model (at least for the money I could afford) so I picked up a very similar spec Dell . Same size and shape but all the mounting holes are different - I've had to knock out the metal standoffs from the case (they were pressed into the baseplate) and drill and mount them differently. It hadn't even occurred to me that they would be different!

jakethompson1 wrote on 2020-07-31, 02:03:

I wouldn't attempt a 5170 as the power supply is likely not enough wattage and may not have "modern" connectors like for 3 1/2" floppy drive, etc.
It is true you can connect AT power backward. The rule is black wires next to each other.

I had thought that the 5170's design was the most "pure" AT configuration, and that perhaps a generic AT PSU would be designed to screw into a 5170 and be ready to go immediately (after all, the power switch is on the PSU itself). Guess I was wrong. It sounds like an AT/ATX case and a StarTech ATX power supply with adapter would be the way to go.

Arbuthnot wrote on 2020-07-31, 08:04:

I recently dug my old IBM ValuePoint out of storage to play with but the motherboard has started intermittently failing to POST so I decided to replace it. No luck finding the same model (at least for the money I could afford) so I picked up a very similar spec Dell . Same size and shape but all the mounting holes are different - I've had to knock out the metal standoffs from the case (they were pressed into the baseplate) and drill and mount them differently. It hadn't even occurred to me that they would be different!

Well at least you "only" had to modify the case--I threw out a P4-based Dell I was using as babby's first retro PC because I wanted to run a GeForce FX in it and the PSU was not just physically but electrically incompatible with standard ATX, so there was no hope of an upgrade.

Woolie Wool wrote on 2020-07-31, 15:03:

Well at least you "only" had to modify the case--I threw out a P4-based Dell I was using as babby's first retro PC because I wanted to run a GeForce FX in it and the PSU was not just physically but electrically incompatible with standard ATX, so there was no hope of an upgrade.

Nasty! I wasn't impressed recently when I went to put a large second hard drive in my new Lenovo work PC - it's one of these stupid 12 V only PSUs, with the power for disks coming off the board. If you want more than 2 extra drives (which I might) or a graphics card you need to get an adapter and put a normal ATX supply in.

Just built a 486 with a baby AT board in a mATX case. Atx psu with an atx->at adapter.

Had to drill a few holes to fit newly placed standoffs for the board and swapped the switch from a momentary to on-off switch. Then bought some blank IO shields and cut out the AT keyboard hole.

Wanted a small case so sacrificed some of the expansion slots, hence mATX but would think a full ATX case would be fine.

Case was £18 and have modern psu that is less likely to go bang!

I gave up on finding an AT case for a sensible price.

Nice squelch41, I wonder how many of the slots you lose on a PCI or VLB board though would be PCI/VLB?
At least I only lose an ISA with my current board and full ATX. With PCI I'd lose one PCI, but I think I'd have two left for video card + ethernet card.

jakethompson1 wrote on 2020-08-02, 21:27:

Nice squelch41, I wonder how many of the slots you lose on a PCI or VLB board though would be PCI/VLB?
At least I only lose an ISA with my current board and full ATX. With PCI I'd lose one PCI, but I think I'd have two left for video card + ethernet card.

Not the clearest pic but you get the idea!
lose then 8 bit isa slot and top 2 ISA/VLB.
The 3rd VLB/ISA is accessible so is where my multi io card is

It does fit nicely. Someone good at cutting metal, etc. could make a nice Baby AT case out of a MicroATX...

Another way to memorize how to connect the AT PSU cables to the motherboard:

"Red and red and you're dead"

Imho for me the problems are always these:

1) deciding if an ATX case would be acceptable to have a 386 or 486 system into because after you finish it, I usually feel like it is .. just wrong. Such modern case with such old mainboard even if actually can be fixed into the case it doesn't look right imho.
2) deciding and trying to find a good, complete AT case, that make the system having a time correct sense, so imho a 486 should have a vertical AT case with front led similar to early Pentium builds but a 386 imho should have an horizontal case.
3) when the case is found, and ipotetically having all the components already, deciding the PSU. And imho it's the worst part. Many AT psu I've seen seems that were cheap even back in those days ironically for system that maybe were really expensive, rarely instead depending on the brand (if there were any at all) a good one can be found but still they have 30 years of lifetime behind so anything into those can be at its limits. Not only the capacitors. So an ATX one? A modern cheap ATX psu I don't think might have any "retro" logic into it so 5V, 3,3v etc might not have the stability those components might need who knows, voltages peaks, ripples etc and only after some serious reviewer that confirm some retro oriented test of good brand new ATX psu I'd be happy with those but still it will not have many old drive connectors not any -5V line. But the -5V line it's said only few cards required it.. I don't know.. my mainboard without it had all the kind of strange crash and instabilities with an old Prescott oriented PSU with the AT adapter and without the -5V. So for me IMHO is a requirement at first in any old config of mine even if not maybe required who knows. But if an old ATX -5v enabled psu is choosed they are old themself too... and as discussed lately the ATX complexity introduced much more components into the PSU than an AT one that at one point they might fail themself compared to a simple good AT psu or even before?
Imho the PSU choise is a serious unsolved problem for me, when there're systems having rare and expensive components into them.

386SX wrote on 2020-08-04, 16:05:

3) when the case is found, and ipotetically having all the components already, deciding the PSU. And imho it's the worst part. Many AT psu I've seen seems that were cheap even back in those days ironically for system that maybe were really expensive, rarely instead depending on the brand (if there were any at all) a good one can be found but still they have 30 years of lifetime behind so anything into those can be at its limits. Not only the capacitors. So an ATX one? A modern cheap ATX psu I don't think might have any "retro" logic into it so 5V, 3,3v etc might not have the stability those components might need who knows, voltages peaks, ripples etc and only after some serious reviewer that confirm some retro oriented test of good brand new ATX psu I'd be happy with those but still it will not have many old drive connectors not any -5V line. But the -5V line it's said only few cards required it.. I don't know.. my mainboard without it had all the kind of strange crash and instabilities with an old Prescott oriented PSU with the AT adapter and without the -5V. So for me IMHO is a requirement at first in any old config of mine even if not maybe required who knows. But if an old ATX -5v enabled psu is choosed they are old themself too... and as discussed lately the ATX complexity introduced much more components into the PSU than an AT one that at one point they might fail themself compared to a simple good AT psu or even before?
Imho the PSU choise is a serious unsolved problem for me, when there're systems having rare and expensive components into them.

I think you worry too much... no decent power supply is going to be "at its limits" when trying to power a regular AT style computer with an HDD, optical drive and one or two FDDs. Doesn't matter if it's AT, ATX or whatever. Just measure how much power such computers take from the wall, it probably won't be more than 50W. Now, if we're talking about servers or workstations the situation may be different, but I think this is not the case.

Just make sure you get a PSU from a reputable manufacturer, make sure it's working and call it a day. Refurbish it by replacing fan and caps if you know how to, as those are usually the first parts to fail. Yes, it will die someday, just like everything else in the universe, but if it's reasonably good the chances of it frying your components are very low.

The -5V line is a non-issue unless you have one of the ISA sound cards that actually need it. Any other problem scenarios are edge cases, it won't have any effect otherwise. It definitely won't lead to "crashes and instabilities", at worst the MB may not power up or the BIOS may sound an alarm which can usually be disabled.

Maybe I worry too much but I've seen different PSU acting in different ways, even when new by the way... lately an old AT psu I had that on the label seems to be "a good one" with a 60W system literally did a flame into it just as soon as I switched it on the power button with a big sound and special effects and scary as it can be imagined. Turned out it was a thermistor inside that went badly and burned literally the near components. The capacitors brands told me it sure was a cheap psu but they were the only things still good probably. Years ago an ATX psu I had, just bought new in box, once switched on gave out of the +12v line something like +15 volts and on the +5v something like +7 volts immediately taking with them the hard disk and the connected video card. I remember some more stories into good psu too ending up badly and most of those didn't necessary have capacitor problems (beside others sure did have capacitors gone before showing signal of it but cause I usually check them all inside).
If I build a no rare Pentium whatever machine with generic low-end components I don't usually care a lot about it but if I have a 386 mainboard that lasted 30 years and still working ok I'd like to be a bit more sure of the power source where everything is connected. 😀
About the -5V line, I read about it and usually I beleived it but maybe I found the only mainboard layout that needed it or maybe some of my components (even with the vga only..) needed it but it might be needed for something more who knows with so many pcb layouts that line might have been used also for others pcb logic. My experience with a well tested P4 psu not having that line with my 386 ended up having the strangest behaviours ever seen in msdos; without that -5V with the mainboard I have, of four I/O controller only one worked at all. Maybe a mainboard design flaw or maybe who know I only have the "rare" cards that needs that line. Still I convinced myself that if that was an AT/ATX requirement I suppose there were some more reasons it was required. 😉