Old AT PSU, how do I trick it? (Question INSIDE)

Sean · Post by **Sean** » Fri May 17, 2002 7:45 pm

OK, I spent the past hour or so dismantling the old Pentium 60mhz Gateway. I found that the 145 W PSU inside would work well for testing the noise of fans (as I removed the fan, and the PSU ran fine). However, the only way to get it working was to hook it up for the motherboard. There HAS to be a way to trick the PSU into thinking it's hooked up to the motherboard. Like the Antec PSU Tester, except for AT. The PSU has a switch on it, so it's all good.

Here are a few pictures:

Anyone have any ideas??

Post by **FlyingPenguin** » Fri May 17, 2002 8:03 pm

Unless you have a VERY strange PSU, there's no trick. Flip the power switch on an it's on.

Unlike ATX power supplies, the power switch on an AT PSU is strictly a mechanical 110 volt switch - usually located external to the PSU connected to a bundle of 4 heavy guage wires wrapped in an insulating sheath.

Sean · Post by **Sean** » Fri May 17, 2002 8:17 pm

You are right about the switch, but, when I turn it on, without the plugs in the mobo, I get little spurts of power. It's odd. The fan starts moving for half a second, than stops. I can turn it off, and it continues for a few minutes, than it just sits there.. Here's a pic of the markings:

Lmandrake · Post by **Lmandrake** » Fri May 17, 2002 8:22 pm

You need to put a load across the 5v leads or it won't work...a 2 or 3 ohm power resistors will do...

Jim Z · Post by **Jim Z** » Fri May 17, 2002 9:10 pm

yeah, a lot of supplys won't regulate unless there's a minimum load.

Sean · Post by **Sean** » Fri May 17, 2002 9:12 pm

Isn't a 5v lead a 4pin connector, basically, right? Cause, once I did put a 4pin fan in, and it did the same thing..

Maybe two fans? Cause it had bigger spurts that time.. ANy ideas?

Jim Z · Post by **Jim Z** » Fri May 17, 2002 10:05 pm

fans are usually 12v. The 4 pin connectors have a 12v (yellow or orange) wire, two ground (black), and a 5v (red) wire. The 5v rail needs to be loaded so that it delivers at least an amp or two.

Post by **FlyingPenguin** » Fri May 17, 2002 10:17 pm

I've never seen a standard AT PSU that needed a load. Must be an unusual beast.

Fans are always 12 volts. IF it's detecting a load, it's looking for a 5 volt load not a 12 volt load.

Silly question - you just using this to test fans? ANY 12volt DC powersupply will do the trick. Rummage around your junk drawer for a 12VDC wall-type powersupply.

Lmandrake · Post by **Lmandrake** » Fri May 17, 2002 11:01 pm

Any switching PS won't put out its rated power without a load...

Jim Z · Post by **Jim Z** » Sat May 18, 2002 11:56 am

I've never seen a standard AT PSU that needed a load. Must be an unusual beast.

I have, not surprisingly it was from a Gateway P5-90. Other generic supplies (AGI etc) worked ok w/o a load.