I am trying to make a bench power supply from an old 350W PC PSU that provides 4 lines

  1. 3.3V 8A
  2. 5V 9A
  3. 12V 11A
  4. -12V 1.5A

Here is the connections diagram: connections diagram

I used this step down module to be able the adjust the voltage and current limit on the 12V and -12V lines: "DC-DC Converter Step Down Module 12A"

I used this display to monitor voltage and current: "DC 0-100V 10A Digital Voltmeter and Ammeter Dual Display"

The problem is that when I try to increase the voltage using the potentiometers of the step down module, I hear a burning sound. I don't know what it is, but I feel like if I don't decrease it fast it will burn something. The burning sound increases very much with the voltage increase

Here is a video for the problem Burning sound

Is the problem from the step down module, or is it from the PSU?

  • 1
    \$\begingroup\$ What is a "burning sound"? Different things make different sounds when they burn. \$\endgroup\$
    – brhans
    Oct 21, 2023 at 13:20
  • \$\begingroup\$ Where did the sound come from? \$\endgroup\$
    – Andy aka
    Oct 21, 2023 at 13:34
  • 1
    \$\begingroup\$ Why are you using +12 and -12 outputs for the step down regulator? That makes no sense. Also, if you have not noticed, most questions here about using old PC power supplies for custom purposes like lab power supplies are about why they don't work when used for custom purposes. \$\endgroup\$
    – Justme
    Oct 21, 2023 at 13:47
  • 1
    \$\begingroup\$ @MohamedEssam Of course everything should work in theory and in ideal world. However the supply can output say 10A or more of +12V and maybe max 1A of -12V, so you will damage it. It is not intended to put load between +12V and -12V, at least not if it is more than say 100mA for analog op-amps or similar. \$\endgroup\$
    – Justme
    Oct 21, 2023 at 14:05
  • 1
    \$\begingroup\$ Did you check for minimum loads on the PC PSU's outputs - and provide them? \$\endgroup\$
    – greybeard
    Oct 21, 2023 at 20:28

1 Answer 1


The problem was because of i had installed the step down module on the body of the PSU and a pin of the soldured pins of the step down module was making a short circuit with the PSU body, so i just put an insulator between them :)


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