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Motherboard posting with AT PSU but not ATX PSU

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First post, by stealthjoe

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I got an AT CPU today with a intel i810 chipset dual S370/Slot1 motherboard (KOB 810 DST). It also has both AT and ATX connectors. There is a Pentium 3 550mhz slot 1 processor installed. The board posts fine with the built in AT PSU (200W). However, it seems to have problems when a CD drive is connected. The board goes in a reboot loop just after posting.

So I tried using an ATX power supply (P450B). The board starts but doesn't post. I also tried using a different local PSU with a 45A rating on +5V rail. However it is the same case.

Any thoughts on what could be the issue?

Intel 845GEBV2, Pentium 4 2.4 Ghz, Geforce FX5600 256MB, 512MB RAM, 160GB HDD, Sound Blaster Live! SB0100 - Win 98.

Reply 1 of 3, by byte_76

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Some boards have jumper to select between AT or ATX.

Have you tried clearing the BIOS?

It’s possible that the 5V rail is not strong enough on your ATX PSU.

Reply 2 of 3, by stealthjoe

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I couldn't find any jumpers for changing between ATX and AT. However the board is still connected to the AT connector but no power to that PSU. Also noticed that the power pins of the front panel connector is not populated with any AT wires. Is that specifically for only ATX switch?

Intel 845GEBV2, Pentium 4 2.4 Ghz, Geforce FX5600 256MB, 512MB RAM, 160GB HDD, Sound Blaster Live! SB0100 - Win 98.

Reply 3 of 3, by stealthjoe

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byte_76 wrote on Today, 14:45:

It’s possible that the 5V rail is not strong enough on your ATX PSU.

Any idea how much amps is required for the 5V rail for such a board?

Intel 845GEBV2, Pentium 4 2.4 Ghz, Geforce FX5600 256MB, 512MB RAM, 160GB HDD, Sound Blaster Live! SB0100 - Win 98.

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