Some problems with ATX PSU

[hentai]

Hello everyone, the situation is this: when i press the power switch on PC, the computer won't start because the PSU won't start (used to work fine a few days ago).
There is a LED on the motherboard that shows the 5V standby voltage is present (LED on) when the PSU is connected to mains.
I removed the PSU connectors from HDD and motherboard and connected Pwr_on pin of MB connector (i think 14) to ground and the PSU starts and shows all the right voltages.
I checked the PC power switch and it is good, i have connectivity when it is pressed.
So i guess the only problem is between the switch and the PSU connector on the motherboard.
Can someone tell me if it is safe to connect pwr_on pin to ground wire permanently and to power it up using the mains switch on the PSU itself? will it work? Or mb you have other ideas, anything is much apreciated.

Thanks,
Andrei

 

[mneary]

Check the CMOS battery.

 

[hentai]

Checked the battery, it is fine.
No other ideas? Can someone tell me if its at least safe to short the pwr on pin to ground to force start the psu? can it damage the MB?

 

[blueroomelectronics]

Yep, here's someone doing that.
How to Convert a Computer ATX Power Supply to a Lab Power Supply (with video) - wikiHow

 

[agis68]

to mod a PSU in a power supply is the easyest thing in the electricity world. The only things u have to tweak is the resistor of 11W for starting the system and manage the color cables so to take the appropriate volatge each time.

YELLOW = 12 Volts
RED = 5 Volts
ORANGE = 3.3 Volts
BLACK = Common Ground.

and for the pinout

Pin Standard Color My Color Use
1) Orange Orange +3.3V
7) Black Black GND
10) Yellow Yellow +12V ( I solderd two wires to this pin)
12) Blue Solid Grey -12V
13) Black Black GND
14) Green Green Switch on
18) White Grey/Red -5V
20) Red Red +5V

take a look here The Ultimate ATX Power Supply Mod With USB Charging Ports

 

[hentai]

hmm, i havent made my problem clear i think. I know how to mod a ATX PSU.

My question: is it safe for computer motherboard to use the PSU with the green wire connected to ground.

In other words: can i bypass the power switch on PC case (the one next to reset button) and use just the mains switch from PSU to start computer?
Thanks.

 

[agis68]

hmmmmmmmm......yes and not...but I am not responsible for your actions.....Yes u have to tweak little a bit the PSU......I have a schematic of a typical ATX PSU and i think u can
take any black cable (ground) and connect it in a switcher then take the green cable and connect it to the other end of the custom switcher.....(not the power on Switcher but your custom one)
Some ATX PSU needs some extra mods....like take the grey or brown cable in absence of the gray and connect it with orrange one (+3,3V) or with red one(+5V) for starting the PSU.....Just try them and one will work...If you want to add a LED indicator as an optical sign that the PSU works fine add it like in the schematic

 

[blueroomelectronics]

Your BIOS might have a power on with AC setting.

 

[agis68]

Not always.....and then what?

 

[blueroomelectronics]

If you hold down the power switch (ie GND) it will turn off after 5 seconds.

 

[agis68]

correct! that's why we block this action isin the 11W resistor wich "delays" that signal

 

[hentai]

OK, so i connected green wire to black wire using a small conductor and then placed the connector in the MB.
i started the PSU using this switch from picture **broken link removed**

PSU starts, CPU cooling fan on MB starts but cooling fan from video card doesnt start and i get no signal on monitor.
Is the MotherBoard busted?

 

[blueroomelectronics]

Hello everyone, the situation is this: when i press the power switch on PC, the computer won't start because the PSU won't start (used to work fine a few days ago).

Yep might be busted, could be anything though. Does it beep?

 

[hentai]

Nope, no beep. When i pressed the buton the power led blinked like 3 times and nothing after that.

 

[Hayato]

Remove the Video Card and see what happens.

 

[Sig239]

Hello hentai,
Perhaps you may have a bad connection from the PSU connector to the motherboard connector. Look for bent pins or sockets in the connectors, if not, then maybe a bad/broken solder joint.

Did you check the voltages under load? Pop the case off the psu and inspect for obvious problems such as blown caps, burnt resistors, hot spots on the board etc. It would be a shame to go through the hassle of replacing the mobo only to find it was the power supply (which is much simpler to fix).

Also check for blown caps etc. on the mobo.

Joe

 

[hentai]

I replaced the video card with another one and the same response. Checked the connectors its good. I tested with different power supply as well. Inspection of the Mboard shows no blown caps.

I think i will throw the towel on this one...

 

[Sig239]

Man that sucks! I just went through a mobo "transplant" earlier this year. Of course, I ended up replacing the psu, thinking that was it at first. Then the HDD. then finally the mobo. Should've just started over, but it was too late once I started buying the pieces. ohh well. Good luck.

 

[agis68]

Yeah I know, and when happens somethinng like that u hate the
computers. It sucks!!!