No -5V output, yet still working

Hi!

I have a power supply tester that tests each line of a PSU for the correct rating (voltage). From all the lines, all LEDs are lighting up, except for the -5V. Yet, the computer is still working correctly. I double checked the PSU tester with another PSU, and this one had all lines working correctly including the -5V, so the PSU tester is working well.

What is the -5V line used for? Do I really need it for the computer to run correctly? What can go wrong if I use the PSU which is not outputting -5V on that line?

Thanks in advance!
14 answers Last reply
More about output working
  1. If your using a mobo with 24-pin atx connector then there would be no -5v input. If you would check the specs of the 24-pin atx, you would see that the -5v is already omitted from the pins. This is due to the fact that -5v is obsolete and no longer needed by newer mobos which uses 4-pin 12v atx connector. This is also the reason why the 12v rail wattage of a PSU is more important today because it is the one who powers up almost everything in the PC. -5v pin is usually used by older mobos with 20-pin atx. Hopefully that may give light to your question.
  2. Thanks a lot for your reply! So the -5V not working does not indicate a faulty PSU? Are there any other 'obsolete' lines, so that I can keep that for future reference?

    Thanks again
  3. There might be some pins aside from the -5v but they are for grounding purposes. The main indication of a faulty PSU is not delivering power (busted).
  4. I thought it might be reason, as the computer is behaving very unstable and most of the times hangs at bios (post code 0075).

    However I tried a perfectly working PSU (with even the -5v line), and it still behaved the same. I'm assuming it's the mobo faulty. Thanks once again!
  5. You're system freezes (post code 0075). Have you tried running memtest? Do you overclock your system?
  6. can't come to the point where i can run MemTest :/ It hangs exactly after it posts the total amount of RAM in the system. I tried changing ram, still doesn't work. I've posted an appropriate thread about this prob in the mobo forum. No, the system is not overclocked.
  7. Sounds like bad ram or wrong voltage. Read the stickys about ram.
  8. I tried 3 different sticks of RAM, and also resetted the BIOS to factory settings, still nothing :/
  9. I went through the whole list. This is not a new build, it was working perfectly and now after about 2 - 3 years it's having this problem.

    I've changed everything except the CPU and Motherboard, and only have the graphics card connected (no HD, CDs/DVDs or floppys).

    Do you think its a bad motherboard? I'm assuming that is the reason, but I would like to be sure its the motherboard before changing. Personally, every fault that I have ever seen on a bad computer never resulted in it being a bad CPU. Maybe it's just by coincidence, but I always rule out the CPU being the problem, since I've never seen a bad one in quite a good amount of computers
  10. Keep in mind that the PSU tester does not put any load on the PSU. If you strip everything out except the PSU and CPU & HSF - including memory and the video card, when you boot, you get a series of long beeps indicating memory problems. If you get silence, one of the three parts left (PSU, motherboard, or PSU) is the problem.
  11. Yes, I get the series of beeps if I strip everything out. Placing the RAM and GFX again, I can get up till the RAM check, and there is a post code 0075 in the bottom right corner.
  12. just give a heat on SIO chip ....it might help
  13. Woohoo, 3 year old thread
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