So I am looking to assemble a 386 or 486 desktop. I have some of the components already floading around from saving things over the years. Main thing I am missing is the motherboard and the case. So I am wondering if any of the new cases and and power supplies out there are compatible with the older motherboards. I am going to probably get the motherboard from e-bay as their are plent out there, the case is where I am stuck....
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Building up a 386 or 486 machine
- Thread starter Frozen001
- Start date
krebizfan
Veteran Member
A 386/486 motherboard will likely be in either AT or Baby-AT form. Avoid proprietary and LPX (riser card) form factor since they require weird cases and often are cheap low quality motherboards.
Some ATX cases are still designed to take AT and Baby-AT motherboards. Check the documentation of the case before buying to make sure it has the extra couple of attachment points. For power supply, there were adapters that would let the typical ATX power supply connect to an AT motherboard. Many vendors still sell AT power supplies so that is a simpler option.
The following store offers period looking AT cases and powersupplies: http://baber.com/coop/oe/at_cases_motherboards_keyboards.htm
VLB motherboards can be a special issue for selecting a case. VLB cards tended to be big so smaller space saving cases will not work with them. Some cases have drive cages or support bars that extend into the area a VLB card would be placed. Check the return policy.
Some ATX cases are still designed to take AT and Baby-AT motherboards. Check the documentation of the case before buying to make sure it has the extra couple of attachment points. For power supply, there were adapters that would let the typical ATX power supply connect to an AT motherboard. Many vendors still sell AT power supplies so that is a simpler option.
The following store offers period looking AT cases and powersupplies: http://baber.com/coop/oe/at_cases_motherboards_keyboards.htm
VLB motherboards can be a special issue for selecting a case. VLB cards tended to be big so smaller space saving cases will not work with them. Some cases have drive cages or support bars that extend into the area a VLB card would be placed. Check the return policy.
Scali
Veteran Member
Yes, a real AT power supply is the safer bet.
ATX2 (the newer 24 pin version) does not have a -5v line.
So if you use an ATX2->AT converter, you won't get -5v. In most cases you get away with it, but there may be some hardware that won't work.
Agent Orange
Veteran Member
All of the above is good info. Cosmetically, if you stuff a 368/486 in to an ATX type case you will be left will a gaping space where your feature bezel snaps into your ATX case. Also, you'll have to fish around for an old type ATX power supply that still has the facility to plug into your motherboard (AT style power connector). There are adapters (ATX to AT) that can be had for a few dollars, however. Personally, I wouldn't do it - not worth the hassle. If appearance isn't a problem for you, then you're good to go. You ought to be able to find an AT style case in your area without breaking the bank.
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gslick
Veteran Member
If you're shopping on eBay for some of the parts you could find an AT case there too. Here is one example from a quick search for around $100 shipped. Maybe they would accept a lower offer, or maybe you could find one less expensive:
http://www.ebay.com/itm/181642387708
I put together a 486 VL-bus system with a motherboard from eBay in the last year and used a basically new AT case with power supply that I picked up for around $10 from a local PC recycler (RE-PC in Seattle). The other 486 I have is a Deskpro 486-33M EISA system that I recently got off of eBay as I wanted an EISA desktop system just for the heck of it.
Yeah, looking at the price of AT cases online, I considered myself pretty lucky that my parents still had the case from their first 486 intact. I remember taking all the parts out of it when I was younger and for some reason I couldn't find the motherboard or the I/O card anywhere when I went to put it back together recently. Luckily I had a 486 VLB motherboard laying around that I had purchased off eBay at a really low price years ago before people decided they were kind of a collectible, so I just used that, although I did have to rewire most of the stuff on the front panel and spend nearly $50 on a CPU upgrade for the thing so I could get the speed I was used to out of the machine (it's a 5V motherboard and doesn't support the 3.3V DX4-100 that was originally in the machine, so what I ended up doing was dropping in a 133 MHz 5x86 upgrade in since it was listed at the same price as both most 3.3V 486 motherboards I saw and the only 5V-to-3.3V regulator socket I could find).
If you opened your eyes, you would see that is the same seller, using a different internet ID.
http://www.ebay.com/itm/181642387708 look that brown table that AT case is standing on.. On ebay you will see the same (guess maybe iam blind?)
There are a few drawbacks with an ATX to AT converter. -5V is one. The other one is the fact that modern PSUs are mainly focused on +12V, so it must have sufficient 5V and 3.3V wattage. Also, since 386 class systems draw significantly less power than modern systems, the PSU must be OK to operate at low total loads (I don't think there will be a problem, but it won't be operating in the most efficient way)
On the other hand, AT PSUs are aged and modern ATX PSUs have a better overall quality. I've been measuring the line volts of some of my AT PSUs. Some of them were found OK (typically those that were branded, eg IBM, Infoquest), others were just unacceptable, as I've been reading voltages as low at +10.5V for the +12V line, or they just shut down the system suddenly etc. The thing is that even those PSUs were powering on the system and it seemed to work OK. Considering that by the AT days I was buying a PC case that had the PSU included and all of it was affordable priced, I don't expect any high quality PSU inside. Now let that cheappy PSU age for 25 years and I wouldn't really put my vintage hardware in it.
Much like I suggest for todays PC, a good PSU is a must if you care for your hardware. So whatever you end up throwing in it, make sure it has a quality insurance. I wouldn't trust an aged AT PSU without testing it with a multimeter under idle and load first.
Scali
Veteran Member
I agree... To be clear, with "a real AT power supply" I meant buying a NEW one, as various places still sell them. Using a dusty old PSU may indeed be troublesome if it's not a decent brand PSU. Like you, I generally just used the PSU that came with the case in those days, and the PSUs have pretty much all died. I have only one of them left.
My older XTs however, they still work fine, with their custom IBM/Philips/Commodore OEM PSUs.
I never had an AT supply die on me (have seen one that was DOA in somebody elses case I inherited) and I still have over a dozen here in use or as spares. The major penny pinching on power supplies seems to be after the switch to ATX and those flimsy cases they were sold with.
Chuck(G)
25k Member
If you can find an old ATX power supply that doesn't have the separate 12V connector(s) for CPU power, you probably have one that supplies -5V on ATX pin 20. Almost any 20-pin PSU will fall into this category. Otherwise, you can run a small (e.g. 79L05) voltage regulator from the -12 pin to supply -5 (the spec calls for very low current draw (it was mostly used for NMOS substrate bias on 16Kbit DRAM chips).
k2x4b524[
Veteran Member
What causes most of these older supplies to fail? I'm sure replacement caps, filters, fuses, can all be sourced. Older power supplies can be had cheaply enough, shouldn't be too hard to refurb them, should it?
Chuck(G)
25k Member
Mostly aging/failing capacitors, but occasionally failed semiconductors.
sergey
Veteran Member
Usually input capacitors (high voltage electrolytic) fail, and frequently they take transistors with them
-5V - Some sound cards (e.g. Creative Sound Blaster) use this voltage for opamps. Some cards use -12V/+12 instead.
lowen
Veteran Member
One 'AT/ATX' dual-use case I had included a 'feature bezel' with a single keyboard hole in the correct place for the AT keyboard connector. You might still be able to find such.