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How do I test this PSU? Answered

I had got this PSU for free from PC world, the guy who gave this to me does not know if it works or not...

This is my first PSU, I never used one before...

So I am asking you how to test this PSU. I hear they have safety wires that must be connected to another wire or something - I don't know...

I hope you can help me... Thanks!

Yay! My PSU works :-)

Thank you all who helped me!

And even better, I do not need to use a power resistor to keep the PSU on!


Then why does mine work without it?

It will work without it but its not good for it, like a car running without oil, it will go for a while and then...

Oh, okay, than I will add a load resistor on the 5v line.

I am going to use an 10Ω 5 watt resistor because:
5V ÷ 10R = 0.5I
5V x 0.5I = 2.5W
Using a 10Ω resistor across the 5v line will waste 0.5A or 2.5 watts of electricity.

Oh, Then the 10W 100ohm that i scavenged out of a emergency exit sign is too big?

No, the higher wattage is not a problem, it just saves space and money (if you are going to buy one).

Oh, When I put it on the 12v line it gets hot, but on the 5 volt, it rarely does anything


12V ÷ 10R = 1.2I


12V x 1.2I = 14.4W

You were overloading the resistor on the 12 volt line, 14.4 watts was going through the 10 ohm resistor.

Okay.... I modded it and now the PSU turns on for a second then turns off, Troubleshooting time :-(

I just unsoldered the output wires and put in some other connectors,last time i tried it, it didn't turn on at all ;-(

I know why it didn't turn on at all, i must of pulled the main off the power connector, I'll report back when i have done it

Okay, I done it, It turns on but I need to keep tapping the signal wire with the ground for it to work, It used to work but now it needs to be pulsed..........

What! That is really weird... I guess you need to add in the 555 timer...

Yeah, a lot of my PSU's need to be pulsed, I just wonder what component was/is blown.......

lot of my PSU

I thought most of your PSU's are "blown", they just need to be pulsed to work?

Well I have a couple that do that (3 or 4) but i just think there's a blown component in there somewhere....

Yeah, Thats gonna take a day worth of full going troubleshooting

I'm guessing that it might be the LM339N Because that has been in every PSU i have ripped apart

They will usually all work without it but they don't reach the output voltages until there is a load.....

Yeah, On the 5 or 12 volt side?

The resistor might be a good idea, i think i sorta messed up the circutry inside a 400w one by not having a load

My 200 watts PSU does not need a power resistor, it works just fine.

I was saying it might be a good idea to always have a load there because i nearly burnt out my 400w psu by not having a load...

Why did your PSU nearly malfunctioned when there is no load resistor?

I don't know, i think just because it was a higher wattage or well i don't know, most people say to have a power resistor to keep a load or....

Yeah, it might be something to do with a higher wattage PSU...

Yeah, I did that same thing to my ATX PSU and it works like charm! With out using a power resistor!

. If it has a 20-pin connector, jumper the green wire to a black wire and it should power up. You may need to have a load on the PSU for it to stay on.

Thanks, and what about the gray wire called (P.G. SIGNAL)?

From http://pinouts.ru/Power/atxpower_pinout.shtml :
8 - PWR_OK - Gray - Power Ok is a status signal generated by the power supply to notify the computer that the DC operating voltages are within the ranges required for proper computer operation (+5 VDC when power is Ok)
. Shouldn't be needed for the PSU to run. It's to tell the mobo that the PSU is operating properly. If you don't have 5V on that line, the PSU thinks something is wrong with itself.

Wow, thank you for all of this helpful information, I am going to test my PSU tomorrow...

. Bookmark the Pinouts site - VERY handy.

Yes, I will.. Thanks! :-)

And my free PSU works! And I don't need a power resistor to keep it on! :-)

yep, get a big fat 8 or 10 ohm resistor from radioshack (somethingg reater than 10 watts) and put it between +5 volts and ground.