ATX Power Supply Problem???

[Naw_S]

i've got an atx power supply to repair,when i power it i get all the required voltage negative that is -12 and -5,can anyone tell me what component could do that.

 

[v_c]

Are you saying you are getting the negative of the voltages that you expect? Are you sure you are measuring these voltages with the common point at ground? I believe you should have a +5V, +12V and -12V supplies with respect to the common ground. Can you verify that your measurements?

Best regards,
v_c

 

[Davood Amerion]

Output voltage polarity can not be reversed in power supply.

 

[Naw_S]

Are you saying you are getting the negative of the voltages that you expect? Are you sure you are measuring these voltages with the common point at ground? I believe you should have a +5V, +12V and -12V supplies with respect to the common ground. Can you verify that your measurements?

Best regards,
v_c

yes i'm getting the negative voltages and yes i measuring with the common point at ground,do you have any idea what component can do something like that.

 

[Johnson]

Measure them with respect to the chasis, which is ground!
Do you have replaced any component?

 

[Naw_S]

no i didn't replace any component,i yes i measured it with respect co ground.

 

[cyberrat]

You sure that your meter leads are the right way aroung? lol

What is the main IC in the PSU?

 

[Naw_S]

yes i'm sure the meter probe was the right way.

 

[cyberrat]

That was humour... lol but you did not answer the question about the IC, what ar ethe markings on it?

Have you got any ATX diagrams? as some are available (usually for the 494 version).

 

[Naw_S]

i don't remember the marking on the ic and i'm not at work so can't check it but i remember the mark of the power supply,it is a bitson power supply,i don't have its diagram.

 

[cyberrat]

OK, well if you find that it has a 494 IC in it then there are several diagrams available.

Added after 18 minutes:

When you say that you are measuring wityh a reference to ground, what are you calling ground?

Are you using the black 0v wire that is accompianed by 12v on the HDD leads?
Or are you using the chassis earth?

Check the PCB for dry joints, especially around the big transformer, if the ground pins of that are not connected correctly then you may be getting a floating ground.

 

[Naw_S]

i'm using the black 0v,i always use the black wire as ground to measure the voltages of the red and yellow wires(+5v and +12v) and i always get +ve values.

 

[cyberrat]

So your measuring an ATX PSU, using the Black wire as your reference.

Are you saying that your getting +5v and +12v on some wires and -5v and -12v on others?

Because that's what yor supposed to get.

If not can you explain a bit more what your getting and exactly where you are getting it? (connector/pin#)

 

[Naw_S]

no on good atx power supply i get the +5v and +12v but on the bad one i get both value negative.

 

[cyberrat]

Do you also get the correct negative voltages on the proper negative rails (-5 & -12) ??

 

[the_risk_master]

What happens when you connect it to your main board , does your PC boot fine?

Resolution:
You can connect an inverting amplifier at those terminals that give negative voltages to recover the desired positive voltages.

 

[VSMVDD]

every day

a pal arrives with a f..... atx psu

best is to replace the psu and move on

use the fets and caps etc.... from it in your own projects

and throw the old pcb to the salvage dump


and buy another its cheeper than even replacing one semi in it


this topic is a waist of effort to cure such redundant psu

as most of them are with heinsight very badly designed anyway

and the reason it blew up ??

well maybe its too small for the gamer who blew it up in the first place

main answer is
replace it and utilise whats left efficently . :!:

 

[Naw_S]

i know its cheaper to buy another one and the client alredy buy a new one,it is me who want to repair it to have some experience.

 

[cyberrat]

On a similar note, does anyone know what the -5v on ATX psu's is for?

I just bought a nice 550w psu cheaply but it turns out to be ATX2 without the -5v.

 

[sawwa7]

hi there
it's normal to have both -5 and -12v , u just miss out the other +5 and +12 and +3.3 v .
ur question shouldn't be why i measure -5 and -12v , it should be about the the other missing supply rails .
also u have to specify what chip used in the power supply as PWM .. commonly used is 494 chip , but there's many other appears in the market today
Kind Regards