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Power controller chip to turn on ATX

Hi Guys,

I have got a mobo here that is dead. I have done all the usual stuff like trying new PSU, bench testing etc. Its dead - as in no fans, no nothing when you hit PWR button - PSU doesnt even come on.

I connected the ATX molex from the PSU and shorted Green (PWR ON) with GND on the molex and the PC came on. All seemed fine.

I think there is a IC on the motherboard between the PWR BTN headers from the power on switch and the ATX header on the mobo that tells PSU to start up.

I am trying to find this IC.

I have attached a image of the mobo with some of the IC's that seem possible labelled.

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Interested to know if anyone knows which IC controls the PSU and tells it to turn on? Someone else suggested this function was handled on the CPU since P4, but I am not sure about that.

Thanks

-Al

RT9237 :

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93705CF :
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952001AF :
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2N03L :
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LD117 :
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RT9602 :
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Reply to
Al
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On Tue, 27 Oct 2009 01:07:23 -0700 (PDT), Al put finger to keyboard and composed:

Eek, you have a motherboard sitting on carpet!

I suspect it would involve the chipset.

This web site has a large number of circuit diagrams for pre-1999 DTK motherboards and PSUs. It may be good for reference purposes ...

DTK Mboard circuits:

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- Franc Zabkar

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Reply to
Franc Zabkar

The MB circuit only tells the enable circuit inside the PSU to let the PSU turn on. To what voltage does the PWR_ON (green wire) fall when you push the ON/OFF switch? The MB must pull this wire lower than 1.5v for the PSU to turn on. I have seen enable logic failure modes where, for example, 1.2v would not turn the PSU on, but 1.0v would. Check that voltage level before replacing any ICs on the MB.

Reply to
UCLAN

When I hit the pwr button that voltage level doesnt change.....(and the switch is fine)

Reply to
Al

Hmmm...could still be a short in the pull-up in the PSU, but I doubt it. Likely something went bad on the MB, but why? It's not a usual failure. How old is the MB?

Reply to
UCLAN

On Wed, 28 Oct 2009 10:18:59 -0700 (PDT), Al put finger to keyboard and composed:

What are the standby voltages at the on/off pins on the motherboard header? If there is no +3.3VSB or +5VSB, I would check the LD1117 linear regulator near the ATX Molex connector.

FWIW, my old socket 7 motherboard uses an SiS 5597/5598 all-in-one chipset. The chip has an ONCTL# output pin which controls the PSU's PS_ON input, and a PWRBT# input pin which appears to connect directly to the on/off "power button". This is debounced internally by the chipset by means of a 30ms delay. The 4 second off timer is also handled internally by the chipset.

SiS5597, Silicon Integrated System, Pentium PCI/ISA Chipset:

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- Franc Zabkar

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Reply to
Franc Zabkar

th

SU

u

Hi Franc,

Excellent suggestions. There is 5v on the On/Off headers.

This motherboard (ECS L4S5MG/561) uses the SiS561 chipset (northbridge?) but whats the other chipset under the black heat sink? southbridge?

How do I work out the number of the other chipset short of degluing it?

-Al

Reply to
Al

Is the +5V standby output from the PSU okay?

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Reply to
Bob Larter

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