VOGONS


First post, by kegepet

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I have an Intel Advanced/AS socket 7 AT motherboard that I'm currently setting up. It's an early Pentium board with a 430FX chipset, and apparently does not put out the full 3.3V PCI voltage. I get a "1 long,2 short" beep code when I booted up for the first time. The manual indicates a problem detecting the video card, and it's probably because the card I installed (a cheap RAGE XL) requires the 3.3V. There is a supplemental power connector on the board (see pics), and my ATX power supply, which I have hooked up via an adapter, also just happens to have a supplemental power connector (see pics). But if you'll notice, in the photo, two of the wires are the correct 3.3V orange, but the first wire is red, which is 5V. So evidently this power connector is not exactly the same as the one required by the board. I was searching around on ebay and couldn't find the necessary adapter. Should I try cutting the red wire and tapping one of the orange wires, splicing it onto the severed red wire leading to the connector? Or would this be a terrible idea? What do you think?

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    ATX PSU's mystery 3.3v/5v connector
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Reply 1 of 8, by TheMobRules

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I suppose you could do that, there are some AT power supplies (usually from OEM systems) with the additional 3.3V power connector, and it is in fact 3 +3.3V and 3 GND. On the other hand, I never had a problem with PCI video cards when leaving that connector unplugged, are you sure that is the problem with your card? Intel claims in their manuals that they added it for "full PCI compliance", but it was never clear to me what that meant.

Reply 3 of 8, by kegepet

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TheMobRules wrote on 2020-07-12, 05:32:

I suppose you could do that, there are some AT power supplies (usually from OEM systems) with the additional 3.3V power connector, and it is in fact 3 +3.3V and 3 GND. On the other hand, I never had a problem with PCI video cards when leaving that connector unplugged, are you sure that is the problem with your card? Intel claims in their manuals that they added it for "full PCI compliance", but it was never clear to me what that meant.

from the manual:

PCI 3.3 VOLT CAPABILITIES To maintain strict compliance with the PCI specification, the motherboard provides a connector which c […]
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PCI 3.3 VOLT CAPABILITIES
To maintain strict compliance with the PCI specification, the motherboard provides a connector which can be used to
route 3.3 volt power to the PCI slots. The connector may be used with a separate 3.3 volt power supply or with a
custom designed voltage converter. Note: The on-board 3.3 volt regulator provides power for the CPU, PCIset and
L2 cache only, not the PCI slots

That last part makes me think the pci slots are getting no power at all, but this probably isn't so. I wish the manual would be more clear.

Reply 4 of 8, by chublord

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My Valuepoint 486 motherboard has the same connector, and I had the same question. The factory PSU didn't have the plug for it and so far there hasn't been any issues with the PCI card.

IBM Valuepoint 486 DX4-100, Opti 802G, 50 MHz FSB, Voodoo1+S3 864, Quantum Fireball EX 4.0 GB, Seagate Medalist 1.6 GB, 128 MB FPM, 256k L2

Reply 5 of 8, by kegepet

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Well I just got finished rewiring the psu (photo attached) and everything works now. I believe older PCI-based video cards required 5V and will work with older boards without additional power requirements. Whereas some, but not all, newer ones, specifically PCI 2.0-compliant cards, require 3.3V. And many will work with both. I did see another post here on vogons about the Rage XL requiring 3.3V, so I guess that's it. Oh, and I should mention, I did try another newer PCI video card, specifically a TNT2 M64 Dell OEM card. That, too, did not work without the additional 3.3V power.

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Reply 6 of 8, by Horun

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Nice work ! Yeah my Riva TNT PCI is a 3.3 card iirc. Most 3.3v PCI cards have a second groove on the edge connector. I bet an old S3 Trio64 would have worked w/o the extra power cable as they are 5v PCI (unless the chipset is wired to register Video only if the 3.3v is connected whether the card needs it or not)

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. https://archive.org/details/@horun

Reply 7 of 8, by kegepet

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Horun wrote on 2020-07-12, 20:53:

Nice work ! Yeah my Riva TNT PCI is a 3.3 card iirc. Most 3.3v PCI cards have a second groove on the edge connector. I bet an old S3 Trio64 would have worked w/o the extra power cable as they are 5v PCI (unless the chipset is wired to register Video only if the 3.3v is connected whether the card needs it or not)

Thank you. Yeah I bet you're right about the S3 Trio64. Unfortunately, I don't have any older cards to try right now. But, I still can't figure out why they made it optional. The manual does mention an onboard 3.3v regulator--why doesn't it also supply power to the PCI slots? I know that the 430fx chipset this board has is a repurposed socket-5-era chipset, which probably predates PCI 2.0.

Reply 8 of 8, by Horun

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Short answers: Intel also made the same board labeled Intel Advanced/ATX at the same time, which used an ATX PSU (and ATX back panel) which does supply the 3.3v for PCI. I think it was at that time where some companies were building both AT and ATX of same board during the transition from AT to ATX.
In general the 3.3v regulator on AT boards has always been for CPU support not PCI, and Intel did the design work for that so it explains why it needed an external 3.3v supply.... just my opinion.

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. https://archive.org/details/@horun