PSU works, but connected to motherboard does not

[ciki022]

I have an problematic 500W psu and problem is that when I test PSU on the table, nothing connected, it is working and giving all proper voltage ( 3,3, 5 and 12 V )
But, when I connect it to motherboard, computer wont start, the PSU wont start either ( fan is not revolving )
Motherboard is MSI with H66 chipset, Celeron G1610 and 2 GB DDR3, nothing else
When I disconnect 4 pin motherboard connector, PSU starts to work, but computer, that is normal, doesnt
I also tested with an older computer, P3 on 800 Mhz, CD and hard drive, and PSU worked well, just for testing I installed Windows XP and works well
I concluded that PSU works but if motherboard needs more watts, PSU fails
Question is : which PSU component is responsiblle to give proper voltage under heavy load ?

Thanks in advance

[rogfanther]

Re: PSU works, but connected to motherboard does not

The motherboard could be faulty also. Have you tried it with a known good psu ? Also, which is the brand / model of the psu ? Pics ?

[ciki022]

Re: PSU works, but connected to motherboard does not

Motherboard is not faulty, I tried another PSU, and works well, and the brand is Blueberry 500w

[rogfanther]

Re: PSU works, but connected to motherboard does not

Model and inside pics, please.

[Escort Eagle]

Re: PSU works, but connected to motherboard does not

What is the Part Number of the controller IC ?

[ciki022]

Re: PSU works, but connected to motherboard does not

First I have to apologize that I gave You wrong brand name.
It is not Blueberry 500W ( I mixed up this PSU and Blueberry 500 W PSU, which is not working at all - doesnt have burned parts, just fuse burnes, when I replace fuse, it burnes again )

This problematic psu has no name, and I think, it is custom ordered PSU.
Images are attached and You can also see part number of controller IC.

[ciki022]

Re: PSU works, but connected to motherboard does not

First I have to apologize that I gave You wrong brand name.
It is not Blueberry 500W ( I mixed up this PSU and Blueberry 500 W PSU, which is not working at all - doesnt have burned parts, just fuse burnes, when I replace fuse, it burnes again )

This problematic psu has no name, and I think, it is custom ordered PSU.
Images are attached and You can also see part number of controller IC.

[rogfanther]

Re: PSU works, but connected to motherboard does not

First I have to apologize that I gave You wrong brand name.
It is not Blueberry 500W ( I mixed up this PSU and Blueberry 500 W PSU, which is not working at all - doesnt have burned parts, just fuse burnes, when I replace fuse, it burnes again )

This problematic psu has no name, and I think, it is custom ordered PSU.
Images are attached and You can also see part number of controller IC.

Instead of "custom ordered", I would venture "crap ordered". Wel, the others may expain better than me, but it seems to be an old design, suited for P3s, early p4s, AMD Athlon XPs, etc. From the looks of it, something about 200 to 250W tops.

As you say it worked ok in a P3, and didn´t power in the MSI, I believe it is just a case of psu not being able ( by design ) to supply the necessary currents for the motherboard ( you didn´t state the exact model of MSI motherboard, but I suppose it is for some fairly recent cpu ( core quads, i3, i5, etc... )

Basically, I would suggest you to install it in the p3 machine, and find a good , reputable brand for the newer machine.

[ciki022]

Re: PSU works, but connected to motherboard does not

Yes, this PSU is old, built in 2007 ( see first image )
But, last three years this PSU powered Athlon 3000+ on AM2 motherboard, with 2 GB ram and one hard drive and one DVDRW drive, without any problems
Because of that fact, I think this PSU is not suited just for P3, early P4, Athlon XPs, like You wrote, but it can power some modern systems
I think that problem is in one/some psu component/s that are failing under heavy load, like I wrote in first post, I just dont know which one/s

[goodpsusearch]

Re: PSU works, but connected to motherboard does not

170-200W max

[rogfanther]

Re: PSU works, but connected to motherboard does not

It is suited for weak things. With due respect, an Athlon 3000+ ( runs at 2.5 - 2.7Mhz, if I remember right ) is not a modern system.
And it has a weak 12V current rating. Considering the age of the thing, and some lies from the manufacturer in the label, we could stipulate that it is able to give about 10A in the 12V line. That would be too weak for most modern systems.

By the way, post the correct model of MSI motherboard and cpu.

[goodpsusearch]

Re: PSU works, but connected to motherboard does not

This thing lacks a proper input filter and has 330uF input caps. It i definitely a bad psu.

[Escort Eagle]

Re: PSU works, but connected to motherboard does not

OK! Here we go ....... As you said when you are connecting 4 Pin Connectors that means +12V connector, then it is Load failing . I think, most probably +12V Diode bracket's one side is open . A diode bracket is consists of two diodes . One of the two diodes may be open . This is why +12V Diode bracket is failing to supply adequate Power when you are connecting 4 Pin Connector . Firstly Check that +12V Diode Bracket very carefully by removing from the PCB and be sure - Is it's one side is open or not . Then give a quick check to other +5V and +3.3V Brackets also .

If you found all outputs Diode Brackets are OK, then do this second job . In the controller section you have B494 Controller IC . If all outputs Diode Brackets are OK, then you have to change this B494 IC . You can use DB494/TL494/UV494/UVX494 anyone of these . You can use KA7500/KA7500B in substitute of B494 . Because TL494 and KA7500 are same .

Both steps Images are attached below . And show us what is the result ......

[domas]

Re: PSU works, but connected to motherboard does not

when plugged to MB, please check the voltages on the big connector if you can access them from the cable side. Any voltages low?? Continuity between PS_on and GND?

Did you try to put some load on in while it is "on the table" ?

[ciki022]

Re: PSU works, but connected to motherboard does not

Escort Eagle,
thanks for the tips, I will try later, at the moment I am at work

domas
I will also try what You suggested
And what kind of "heavy load" I can connect "on the table" ( I tried with two fans and one hard disk, and it was working, but that isnt "heavy load" ) ?

[domas]

Re: PSU works, but connected to motherboard does not

no, i would say something like 5 amps, some 2 ohm resistor, but it has to be high wattage else it would overheat instantly

[domas]

Re: PSU works, but connected to motherboard does not

or a 55++W automotive light bulb

[re-atari]

Re: PSU works, but connected to motherboard does not

In the controller section you have B494 Controller IC . If all outputs Diode Brackets are OK, then you have to change this B494 IC . You can use DB494/TL494/UV494/UVX494 anyone of these . You can use KA7500/KA7500B in substitute of B494 . Because TL494 and KA7500 are same

In addition to the above: the other IC is a LM339. The combination TL494/LM339 was widely used in AT PSU's. They each cost just peanuts.

re-atari

[domas]

Re: PSU works, but connected to motherboard does not

...and in many ATX as well

[senz_90]

Re: PSU works, but connected to motherboard does not

you may remove the transformer to checks that secondary heatsinked diode, it is always more easy than trying test it in circuit may give unaccurate reading.

but it depends on you to remove the diode heatsinked by Escort suggested or removing the transformer. just make it easy for you. i have that PSU too. if im not recall wrong, the brand model is Eyota. crap cheap PSU.. but I think it could be to powering above P4 CPU, i have tested it on my cpu before and it has no problem.

Lack of input filtering makes me afraid for my motherboard safety