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Smack2k
February 17th, 2017, 06:11 AM
I have read and seen many articles about how to short an ATX Power supply to test power for it and then using a multimeter to check the voltages. The articles also mention best to test them under load. But what I dont see in the articles is what exactly is being used to provide the load on the machines. So what would be good to hook up to the supplies to give them a good test with load?

Secondly, is there a way to test an AT Power supply in the same way? Or is the best option to hook up an AT to ATX Adapter and test from the adapter?

lutiana
February 17th, 2017, 07:00 AM
You can buy an ATX PSU tester, which puts a resistive load on it, but I usually just use a HDD. You just need something that will pull amps off of the 12V and 5V rails, a spinning hard drive does this quite well.

And yes, you can use the same process to test an AT PSU, you just don't need to ground out a wire coming from the supply, you can just flip the switch.

One big diff between an ATX and an AT PSU is that an ATX PSU should power up when the PowerOn wire is grounded regardless of a load, whereas an AT PSU will probably not power up at all when the switch is flipped when there is no load on it. I've even seen them push out 12V and 5V for a few seconds before dropping to 0v due to the lack of a load.

Malc
February 17th, 2017, 07:06 AM
A Known working Motherboard and Hard drives are good choices, When i test PSU's i load them up with a good motherboard and a few hard drives and leave the PSU running whilst checking the output voltages over a period of time, I do that with AT and ATX PSU's.

Don't rely on an "ATX power supply tester" as they can often tell you an ATX is good when infact it's not, I have one and only use it because it shows Voltages and PG time on screen, Basically nothing more than a glorified DMM.

Malc
February 17th, 2017, 07:24 AM
It depends on the PSU, Just like some AT PSU's won't power up without a load, Not all ATX PSU's power up without a load either, best thing to do is attach a load regardless.


...One big diff between an ATX and an AT PSU is that an ATX PSU should power up when the PowerOn wire is grounded regardless of a load, whereas an AT PSU will probably not power up at all when the switch is flipped when there is no load on it. I've even seen them push out 12V and 5V for a few seconds before dropping to 0v due to the lack of a load.

Stone
February 17th, 2017, 07:48 AM
And sometimes the puny 3" IDEs aren't sufficient load to get the desired result. A FH 5" Maxtor Monster (or other brand) will surely provide the correct outcome.

MikeS
February 17th, 2017, 08:33 AM
And sometimes the puny 3" IDEs aren't sufficient load to get the desired result. A FH 5" Maxtor Monster (or other brand) will surely provide the correct outcome.
There ya go: start marketing those doorstops of yours as high-tech Universal Dummy Loads!

Stone
February 17th, 2017, 08:35 AM
There ya go: start marketing those doorstops of yours as high-tech Universal Dummy Loads!Brilliant! :-)

Smack2k
February 17th, 2017, 08:44 AM
Thanks for the information.

I ask as I fear the AT Power supplies in a couple of my older PC's (486 and Pentium 1) that I built will go bad and take other hardware with it. They seem fine now, they work and run when the computer is on. But I havent had either on for an extended period of time (hours consecutively) and I am worried about them damaging the rest of the system if I do.

lutiana
February 17th, 2017, 08:47 AM
Thanks for the information.

I ask as I fear the AT Power supplies in a couple of my older PC's (486 and Pentium 1) that I built will go bad and take other hardware with it. They seem fine now, they work and run when the computer is on. But I haven't had either on for an extended period of time (hours consecutively) and I am worried about them damaging the rest of the system if I do.


Grab a hard drive that you don't really care about, plug it into the PSU and unplug everything else then turn the PSU on and just walk away. Come back in an hour and check the voltages, then walk away again and come back and check it every now and again. If you get through 12 hours and the voltages don't change much and the HDD is still spinning then I'd say you have a good PSU.

Stone
February 17th, 2017, 09:05 AM
I ask as I fear the AT Power supplies in a couple of my older PC's (486 and Pentium 1) that I built will go bad and take other hardware with it. They seem fine now, they work and run when the computer is on. But I havent had either on for an extended period of time (hours consecutively) and I am worried about them damaging the rest of the system if I do.Why do you say that?

How would that happen?

Unknown_K
February 17th, 2017, 09:21 AM
I never had an AT power supply take out a motherboard or card. They seem to work or they don't.

Stone
February 17th, 2017, 09:52 AM
Ditto...

And that also includes ATX.

Unknown_K
February 17th, 2017, 10:03 AM
I have read stories about cheap ATX supplies blowing up and taking whole systems with them, but the ones that failed on me (a few over the decades and one with smoke) didn't kill anything.

Smack2k
February 17th, 2017, 01:45 PM
I had read stories of the PSU's taking hardware with them...good to hear from all of you that's most likely not the case....

I will keep the working ones in the systems and load test the pile of others I have just to make sure I dont have anything bad....the caps and boards inside of them all look good, no bulging or anything. Some just need a good, careful cleaning...

Thanks for the assistance with what to do for load and for the AT supply, much appreciated!

lowen
February 17th, 2017, 02:56 PM
A few years back I had a machine with two of the then new 250GB Maxtor SATA drives, the first generation, that had the regular Molex connectors. I was running a version of RedHat Linux, maybe 7.3 or 8, using the Linux software RAID (mdraid) in a RAID 1 configuration. I kept getting degraded array errors, and mysterious bad sectors started appearing on the disks.

After a while of this, I started noticing that it sounded like the drives were spinning down then back up, so I took my oscilloscope and checked the power supply. One of the two 12V rails was glitching badly. So the drive was losing 12v with 5v still up, and if this glitch happened during a write it was causing the disk to "scribble" data off-track. Some of the servo data must have been damaged, since seeking to certain tracks afterwards would error out.

A flaking-out PSU damaged two SATA drives. The PSU in question was a 450W Antec, not an underpowered El Cheapo.

Unknown_K
February 17th, 2017, 03:41 PM
Bad capacitors were a problem with power supplies as well as motherboards.

Malc
February 17th, 2017, 10:09 PM
Capacitors seem to be the bane of electronics, More so if the manufacture used cheapo crappy caps in the first place, Which a lot of them do.