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.

http://www.badcaps.net/forum/attachm...chmentid=12082

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 : http://www.alldatasheet.com/view.jsp?Searchword=RT9237
93705CF : http://www.ic2ic.com/search.jsp?sSe...3705CF&prefix=9
952001AF : http://www.alldatasheet.com/view.js...chword=952001AF
2N03L : http://www.alldatasheet.com/view.jsp?Searchword=2N03L08
LD117 : http://www.st.com/stonline/products...fo/ld1117_1.htm
RT9602 : http://www.alldatasheet.com/view.jsp?Searchword=RT9602

On Tue, 27 Oct 2009 01:07:23 -0700 (PDT), Al put
finger to keyboard and composed:

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

http://www.badcaps.net/forum/attachm...chmentid=12082

Eek, you have a motherboard sitting on carpet!

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.

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:
http://www.dtk.com.tw/tech/circuitm.htm

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Al wrote:

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.

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.

On Oct 28, 8:55*am, UCLAN wrote:
Al wrote:
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.

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.

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

Al wrote:

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.

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

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?

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

On Oct 28, 8:55*am, UCLAN wrote:
Al wrote:
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.

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.

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

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:
http://www.datasheetarchive.com/pdf-...DSA-594853.pdf

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

On Oct 29, 4:02*pm, Franc Zabkar wrote:
On Wed, 28 Oct 2009 10:18:59 -0700 (PDT), Al put
finger to keyboard and composed:



On Oct 28, 8:55*am, UCLAN wrote:
Al wrote:
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.

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.

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

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:http://www.datasheetarchive.com/pdf-...ts-30/DSA-5948...

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

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