VOGONS


First post, by Maleckii

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I recently picked up a Saturn I 486 PCI motherboard that I'm certain was pulled out of a Gateway 2000 system, since I recognize the serial number sticker. I'm fairly sure this is an Anigma board. There's jumpers on board to select 5v and 3.3v CPUs, and 1, 2 or 3x internal clock multipliers, which I suppose means this will support a DX4. This board has something I haven't really seen before - a third AT power connector labelled 3.3v. I haven't powered up the board since I can't find any AT power supply that actually puts out 3.3v - and also I don't have any more cache to populate the sockets at the moment, nor can I fit it in any case I have since it uses PS/2 like every other Gateway 2000 machine I've seen.

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Has anyone ever seen an AT power supply with a 3.3v rail?

Reply 1 of 8, by DeafPK

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I have a computer with such PSU, it even has a fourth connector for 5V standby and soft power-on, just like ATX. However, the motherboard hasn't got the connector soldered on so the 3.3V cable is not in use. You may be able to run your board without it aswell.

"an occasional fart in their general direction would provide more than enough cooling" —PCBONEZ

Reply 2 of 8, by TheMobRules

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I have seen that connector mostly in early PCI based motherboards with Intel chipset, such as late 486 (Saturn, Aries) or early Pentiums. I never had one of those boards myself, however the manuals mention that it's a 3.3V power connector "to maintain strict compliance with the PCI standard". No clue what that means.

Reply 4 of 8, by derSammler

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TheMobRules wrote:

I have seen that connector mostly in early PCI based motherboards with Intel chipset, such as late 486 (Saturn, Aries) or early Pentiums. I never had one of those boards myself, however the manuals mention that it's a 3.3V power connector "to maintain strict compliance with the PCI standard". No clue what that means.

When PCI was introduced, the AT PSUs back then had not enough juice on 3.3V to fulfill the PCI standard. That's why this connector exist. You don't need to care about, unless you plan to connect it to a pre-1994 AT PSU.

Reply 5 of 8, by TheMobRules

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derSammler wrote:

When PCI was introduced, the AT PSUs back then had not enough juice on 3.3V to fulfill the PCI standard. That's why this connector exist. You don't need to care about, unless you plan to connect it to a pre-1994 AT PSU.

But standard AT power supplies do not provide 3.3V, just 5, 12, -5 and -12 volts. The 3.3V line was introduced by the ATX standard...

Reply 6 of 8, by GPA

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Board will run without 3.3V connected without any issues, all mine do at least.
Also, there are ATX->AT adapters on the ebay that have this third 3.3V connector, but be careful if you buy one of those, they are often wired with reverse polarity!. Please make sure to check there the ground is on your board and on this adapter before plugging it in.

Reply 7 of 8, by BitWrangler

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Acer liked to do that. and yah ^^^^ double check that, Acer also had funky wired "AT" connectors.

Basement full of ancient PC stuff, starting to go through it. Most recently toyed with DOS era stuff 15 years ago, so memory might be rusty. So what's this BitWrangler guy's deal ??? >>> Taming the pile, specs to target?

Reply 8 of 8, by derSammler

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TheMobRules wrote:

But standard AT power supplies do not provide 3.3V, just 5, 12, -5 and -12 volts. The 3.3V line was introduced by the ATX standard...

The point was that this connector was only added to get PCI approval. When not connecting, 3.3v is generated from 5v (or not provided at all), which however does not fulfill the PCI standard, since the sum of current is too low (6A is required on 3.3v alone to comply PCI 2.1).