Bench Power Supply From ATX

[Samyaza]

Hello, I'm new to electronics. I own two compaq ATX power supply to be specific the: Compaq ps-5201-4t2.
I tried to find schematics on the web but without success.
It has a 20 pin P1 connector. I tried to use a generic pinout for a general ATX power supply but is not starting without the mo-bo connected.
I thought it needs some loads, so I used 10 Ohm 5W resistors on 12v and 5v rails. Still nothing.
I also tried to put such load on the 3,3 V rail from the P1.
As I said the colours of the wires are different, but I tried them by analogy.
Whatever I do, I can't start the power supply. Any ideas?
I'm quite disperate. I want to use it to make a bench power supply.
Can anybody tell me the pin configuration of the 20 pin compaq PS-5201-4T2?
I've seen they are using separate colour form a standard 2o pin ATX power supply.
They are the same pins but with different colours?
Where should I put loads to start it without the mo-bo?
Thanks!

[jeroen79]

http://i155.photobucket.com/albums/s318/paulpsomiadis/compaq_psu_atx_mod_no2_improved.jpg
You need to ground the PS_ON# to turn it on.

[Samyaza]

I grounded the PS_ON but is not starting.
Also I tried to use 10 Ohm 5W resistors as load on some rails, like the +5 +3,3 +12 and nothing.
Other ideas?

[jeroen79]

Can you measure voltage on the 5V AUX line?

[Samyaza]

nope is not working.. is 0

[prawncrackers]

maybe its damaged? why dont you post pics of the board and maybe we can find the fault if it is damaged.

btw some ATX PSUs have ATX-specific controller ICs which monitor the 3.3v 5v and 12v outputs and will report a fault if the voltages arent right in all 3 pins. that makes it hard to modify the output voltage. ATX PSUs with TL494 ICs are easily modifiable.

[Samyaza]

No is not damaged.. I have two of them and both have the same problem. Is the only atx source model I couldn't start without mobo!
I need to find a way. I want them to make a power bench power supply. I need like two of them. One made from an ATX power supply and another made from a switch mode power supply 24V and 10 Amps. For the other is a little bit complicated with the voltage control and current limiter.
The problem is the LM317 is not working over 2-3Amps, the LT1038 is obsolete and nowhere to be found so I went over this schematic:
http://electronics-diy.com/electronic_schematic.php?id=981
This solves the voltage regulation but... I idon't know what to do about the current limiting.
I need a knob to fix the maximum current for an app and for both of them of course I'll have displays, actually a voltmeter and an ampermeter. The LCD type. In fact I found a nice combo. 0 to 100V cc and 0 to 10Amps in the same enclosure. neat..

[Grayfox]

The wire you are grounding is green PS_ON right?
Not the gray PWR_OK

Try connecting the PWR OK to a red LED with a 220ohm .5w resistor to add some load to it

Think I read that the PWR OK needs to get some kind of signal to keep the PSU on, I know it tells the mainboard that the power output is fine.

Also  you said this is a compaq PSU

Saw this so your pinouts may not be to the ATX spec

[Samyaza]

is a 20 pin P1 not 24. I will try today with the power ok wire.

[Grayfox]

is a 20 pin P1 not 24. I will try today with the power ok wire.

The other 4 pins are
+12v, +5v
3.3v, GND

Pin 14 is PSU_ON in both 20 and 24 pin ATX connectors


It is a wild shot by try connecting the PWR OK to PS_ON#

It might turn on, but I wouldnt rely on this for long term, but doing it for a second should be fine.