Low green wire voltage 3.3v ps-on power atx

Hello friends of the forum
I have an atx power supply that is ready for voltage conditions. The voltage of the purple wire is 5 volts and the voltage of the green wire ps-on is 3.3 volts and the power switch does not start. What is the problem and where is it ?: meh:

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JimB said:

Sorry Electronium, many of us here speak a range of languages, but I am sure that very few speak Persian.

Using Google Translate, I get this:


Welcome to the forum.

JimB

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Reloadron said:

Translation:
Hello friends of the forum
I have an atx power supply that is ready for voltage conditions. The voltage of the purple wire is 5 volts and the voltage of the green wire ps-on is 3.3 volts and the power switch does not start. What is the problem and where is it ?: meh:

ATX PSU pinout. Green is PS_ON and should be 5.0 volts, grounding the Green should force the PSU to start. Purple is 5.0 volt SB (Stand By). You should be seeing 5.0 volts on the green held up by a pullup.

Ron

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electronium said:

The voltage of the green wire is low, I do not know which part to check, as if all the parts are healthy ... and I connect the green wire to the chassis, nothing happens

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Reloadron said:

I assume the PSU is removed from the PC. The voltage on the PS_ON should be the same as the 5.0 volt standby voltage. The PS_ON line is held logic high as a result of an internal pullup resistor. Pulling PS_ON low to ground starts the power supply. Logic low is any of the black wires which are ground. Any voltage measurements should be referenced to ground. Some PSUs when started stand alone need an external load but I haven't seen a need for that in years and it depends on the PSU.

Normally when an ATX PSU fails it is just replaced. Finding a decent schematic and anything beyond some very basic troubleshooting is not an easy task.

Ron

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Reloadron said:

I assume the PSU is removed from the PC. The voltage on the PS_ON should be the same as the 5.0 volt standby voltage. The PS_ON line is held logic high as a result of an internal pullup resistor. Pulling PS_ON low to ground starts the power supply. Logic low is any of the black wires which are ground. Any voltage measurements should be referenced to ground. Some PSUs when started stand alone need an external load but I haven't seen a need for that in years and it depends on the PSU.

Normally when an ATX PSU fails it is just replaced. Finding a decent schematic and anything beyond some very basic troubleshooting is not an easy task.

Ron

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alec_t said:

Welcome to ETO!
What are the markings on the two ICs?

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alec_t said:

So it may be, but that doesn't answer my question. What type numbers are on the ICs (the pics are not in sharp focus)?

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alec_t said:

Thank you.
This site has schematics for various ATX supplies using the TL494. If you spot one which corresponds to the manufacturer of your ATX, that would be a good start to help fault diagnosis.

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