ATX PSU Confusion

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Joel0328

Joined Feb 14, 2018
1
I have recently received a broken PSU. I am posting on this forum to see if anyone has any suggestions as to what the best way to go about locating the problem would be. I would like to eventually convert the PSU to a bench power supply if I can get the PSU running. When I connect the PSU to the power cable and then connnect the PG through hole to a ground through hole, the PSU makes a very small whining noise however I do not receive any power from any of the outputs and the fan does not turn on. At the begging of this little project I removed the solder on all of the cables to the PCB because I did not think I’d need them for the project I was planning on doing but then I find out many people keep those cables for bench power supply conversions. In hind-sight this may have been a bad idea but I’m hoping that I can still get the PSU running anyways.
Hopefully this was enough info.
Thanks,
Joel

Attached is a photo of part of the PCB
more cables can be provided if needed
 

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Tonyr1084

Joined Sep 24, 2015
7,852
Looks like you did a pretty good job of removing the wires. That's not the source of your problems. The problem is elsewhere, and we can't troubleshoot it for you. That's something you're going to have to do on your own.

First, let me start by saying the only way you're going to figure out what's wrong is by powering it up. That means plugging it in. WARNING: You're going to be testing and measuring high voltages. Voltages that can injure you or even end your life. If you're not competent to do this then I'd suggest you find a simpler project. Many of us here have been shocked by mains voltage, and are still here. However, we have no idea how large the community would be if we could include those who didn't survive their encounter with high voltage. So - be careful.

OK, if you've decided to move forward with this then you're going to have to check for mains voltage (120 or 240, depending on where you are). Follow it through from component to component as best you can. First thing you should encounter is a fuse. If power is going through the fuse then that's one problem eliminated. Trace the circuit through the filter coils (toroidal cores wound with copper wire). make sure you have power on both sides of the coil. It's unlikely you'll find any problems there, but you want to be thorough. Depending on how your PS is built eventually you'll find where the AC is turned into DC. Make sure you have full rectified voltage. To know what your rectified voltage would be simply multiply your mains voltage by 1.414. You should also find two very large capacitors that are rated to handle high voltage. Make sure you have full voltage there as well. From there on out - I'm not good enough to know what you should see or where. But it's a start.

Remember, you're working with live power. It's dangerous. Not recommended for beginners. Just so happens I have an old computer power supply sitting on my workbench as a supply as well. Mine has 12 VDC @ 18 amps, -12 VDC @ 1 amp, 5 VDC @ 2 amps and 3.3 VDC @ 17 amps. Most often I use only the 12 V or the 5 V supply. Once I've used the 12 & the -12 for a range of 24 VDC @ 1 amp. So with yours, 5 & 12 volts, should be useful enough. The one thing I had to learn, came here to learn it, was how to power it on. Off hand I don't remember which wire it was, but one of those wires had to be jumpered to another wire. Hence, I was able to install a switch to turn mine on and off.

Good luck with your project.
 

LesJones

Joined Jan 8, 2017
4,174
Also don't forget that to get any output from the power supply other than the +5V standby output the "power supply on" signal (Pin 14) must be connected to one of the common outputs. I agree with Tony. Unless you really know what you are doing and have a good understnding of switch mode power supplies it is best to buy a new power supply or get one out of a PC that is being scrapped. The fact that you asked the question on this forum suggests that you do not have the required knowledge to work safely on this type of power supply.

Les.
 

AlbertHall

Joined Jun 4, 2014
12,343
Some supplies have a minimum load below which they will not power up.
Try connecting a 10Ω 5W resistor across the +5V output.
 

Reloadron

Joined Jan 15, 2015
7,501
A place to start is to look at the 5V SB which should be present with the power supply connected top mains and turned on. With that established measure from what was the PS_ON line which was a Green wire on the old connector, this was pin #14 on the old 20 pin ATX main connector and is pin #16 on the newer 24 pin versions. You should see 5 volts derived from 5V SB. Then as mentioned placing that line to ground should start the PSU, also depending on the version and age some need a load, some on the 3.3 volt out and some on the 5 volt out. Also on some of the older versions Pin #11 of a 20 pin connector was a 3.3 volt sense and should be tied to any 3.3 volt out line.

Ron
 
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