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PC cutting power

TravisHuckins

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Sometimes my DOS PC cuts power. I think it might be because the power supply is old so I ordered a new AT PSU for it. Would it best for me to not use this computer until I put the new supply in. Don't want to risk ruining my hardware. (I think I just answered my own question. lol
 

Chuck(G)

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You didn't say how old the PSU was, what its ratings were, what the PC in question was, nor how heavily you were loading said PSU.

Makes it hard to render an option. :)

If your PSU is very old, the problem may be nothing more than geriatric capacitor disease.
 

TravisHuckins

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You didn't say how old the PSU was, what its ratings were, what the PC in question was, nor how heavily you were loading said PSU.

Makes it hard to render an option. :)

If your PSU is very old, the problem may be nothing more than geriatric capacitor disease.

It's easily 20 years old. So most like likely bad caps. And it was not a heavy load at all. 1 HDD, 3.5 FDD, 5.25 FDD, CDrom, 2 ISA (the old system ran 3 ISA) cards and 1 PCI card. Which a 150 watt PSU handled on the old system. Now this new system has a 200mhz Socket 7 CPU rather than 90mhz Socket 5... 250 watts should have been more than enough. The new PSU is 300 watts.
 

TravisHuckins

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Um, that is what it is... but I paid about $20 less than that. I don't exactly have the confidence to recap a power supply. It's too late to cancel the order anyway. I'd thought I'd give it a shot since it had more positive than negative reviews. I can return it doesn't work right.
 
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GiGaBiTe

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What exactly is wrong with those supplies?

The way they make these new AT power supplies is by taking a garbage ATX power supply design and adapting it with P8/P9 power connectors and a toggle switch.

The designs are well known to be unsafe for numerous reasons, primarily because they cut corners in the design and eliminate safety features like over current and over voltage protection, use under rated parts like diodes instead of a bridge rectifier and omit the transient filtering stage. The power filtering and regulation is usually very poor due to the lack of proper rated capacitors and chokes, resulting in the equipment it's driving being stressed unnecessarily.

The reason these crap designs are used is because they're based on designs from an ancient ATX standard which still provided for the -5v rail, which was eliminated from the ATX spec in 2004. Some ATX power supplies did keep it up until the late 2000s, but no modern design will have that rail. Another consideration is AT machines primarily draw on the 5v rail, which is something else old ATX spec units provided pre-P4 era where these designs came from. Modern ATX designs have most of their capacity on the 12v rail, so even if you had a negative charge pump to get the -5v rail, the power supply would likely malfunction or not work at all.

The best choice if you have an old AT power supply acting up is to repair it. If that isn't possible, then I'd recommend getting an older ATX unit with a -5v rail and getting a Minifit Jr. to P8/P9 adapter instead. It's not a great idea to risk your old equipment with shitty power supply designs.
 

TravisHuckins

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If anyone is selling a refurbished AT 200-300w power supply let me know. (My current PSU is actually 200w not 250). I reinstalled it and it shut off once when I was loading Doom but it might just be finicky about my power. I had it and my CRT monitor and a bunch of other stuff plugged into the same power strip so that might have caused the issue.
 

GiGaBiTe

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At the very least, it doesn't look as cheap as the Athena unit, but that doesn't mean it's good.

The only way to truly know is to open the unit if you buy it.

If you open your current power supply and take a picture, it may show us what's wrong with it.
 

TravisHuckins

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I think I'm gonna try the startech one... From the reviews no one said anything too bad about them and they do mention they are made with quality components (one can hope they are truthful). I'll order one and report back. When the Athena supply gets here I'm just gonna return it.
 
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Unknown_K

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Even the cheap junk AT supplies tended to work ok from what I remembered (until you put to many HDs on them). It was during the ATX era when supplies started getting really bad and would fail taking out whole systems with them. The rise of gaming video cards with huge 12VDC loads didn't help.
 

GiGaBiTe

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Even the cheap junk AT supplies tended to work ok from what I remembered (until you put to many HDs on them). It was during the ATX era when supplies started getting really bad and would fail taking out whole systems with them. The rise of gaming video cards with huge 12VDC loads didn't help.

Most of these new AT supplies are based on those junky ATX designs, which I've been saying the whole time.
 
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