Bad Motherboard? No Power

[gtslabs]

I have no power to the motherboard.
I have verified power to the Power Supply.
I have replaced the Power Supply with a new one.
I have 5V on the PSU MB Purple Wire. I have 5V on the PSU MB Green
Wire. No voltage on any other wires. I thought that Green voltage
should go below 2.4V when switch depressed but no change occurs.
When I jumper the MB Green wire pin 14 to Pin 13 black wire then the
PSU works and all the fans turn.
I have continuity across the switch when depressed. I pulled the switch

pins and shorted but still no power up.
I see no burnt out capacitors.
I tried to power up by removing all power leads to HD,FD,CD, DVD. No
Luck
CPU fan turns freely.
Case fan turns freely.
It is a P4 system but I dont see any model on the acesss side of the MB

other than Made in China!
Is the MB Bad? How can I further test it?

Thanks
Steve

 

[Davy]

Checking with a known good Power supply unit is the first and logical
thing to do, you say the fans turn freely I assume you mean by hand,
otherwise I assume they do not spin when you power up.

Seems that you have a test meter, with the power cord unplugged you
can check the action of the switch with the test meter set to the
ohms range, should read low or zero resistance when the switch is
closed when placed across the switch contacts or its lead.

You don't say how old the mobo is, if more than about two or three
years the bios back up battery may be the problem, but I would have
expected the fans to spin at least, once you remove this battery the
bios will re set to its default settings.

Have you looked for bad caps on the mobo, they may have swollen or
domed tops instead of being nice and flat or may have gunge leaking
out, another fault could be the power lead that connects to the mobo,
the wire's are only crimped and can easily work loose, same with the
connector pin's on the mobo they can become loose due to the solder.

Even with a CPU fault I would expect the fans to spin at power up and
I really would expect the same if the bios battery was at fault but
can not be certain with differing mobos.

The fans are usually operated from the 12 Volt line, which seems to
suggest the PSU is not being switched out of standby.

No 100% clues here I'm afraid but hopefully may give you a pointer, at
least I've 'propped' your post nearer the top of the list.

Davy

 

[Andy]

I have no power to the motherboard.
I have verified power to the Power Supply.
I have replaced the Power Supply with a new one.
I have 5V on the PSU MB Purple Wire. I have 5V on the PSU MB Green
Wire. No voltage on any other wires. I thought that Green voltage
should go below 2.4V when switch depressed but no change occurs.
When I jumper the MB Green wire pin 14 to Pin 13 black wire then the
PSU works and all the fans turn.
I have continuity across the switch when depressed. I pulled the switch

If the standby voltage is +5 volts, and shorting the power switch pins
at the front panel header does not result in PS_ON# at the ATX power
connector going low, then it points to a problem with the motherboard.

 

[gtslabs]

I determined I have a MSI 845 Ultra-C MS-6566 Motherboard.
I removed the CPU fan and heatsink and noticed that the gray coating
from the P4 Chip has worn off and transfered
to the aluminum contact surface of the heat sink. Is that typical?
Could the CPU fried from too much heat and that be the reason the MB
wont energize?

I found a replacement MB for $36 refurbished but wanted to check out
the CPU problem first.
If this combination is not cooling the CPU enough then maybe I should
consider something else.

The problem started a few months after I installed a "NEW ATI RADEON
9600 SE 128MB DVI VGA AGP 10588" video card for my son
to run some game.

Thanks
Steve

 

[larry moe 'n curly]

When I jumper the MB Green wire pin 14 to Pin 13 black wire then the
PSU works and all the fans turn.
I have continuity across the switch when depressed. I pulled the switch
pins and shorted but still no power up.
I see no burnt out capacitors.
I tried to power up by removing all power leads to HD,FD,CD, DVD. No .luck
CPU fan turns freely.

I determined I have a MSI 845 Ultra-C MS-6566 Motherboard.
I removed the CPU fan and heatsink and noticed that the gray coating
from the P4 Chip has worn off and transfered
to the aluminum contact surface of the heat sink. Is that typical?

All P4s I've seen had a silvery coating, not a grey one, and any grey
stuff was thermal grease, but it's normal for that grease to come off
when the heatsink is removed.

Could the CPU fried from too much heat and that be the reason the MB
wont energize?

P4 chips have built-in protection against any overheating not caused by
a blowtorch.

I found a replacement MB for $36 refurbished but wanted to check out
the CPU problem first.
If this combination is not cooling the CPU enough then maybe I should
consider something else.

The problem started a few months after I installed a "NEW ATI RADEON
9600 SE 128MB DVI VGA AGP 10588" video card for my son
to run some game.

Is it possible that your PSU's +5.0V or +3.3V rail has gone bad because
of bad output capacitors or diodes? When you short the green and black
wires together, do you get any voltage when you connect a meter between
any black wire and red wire (+5.0V) or between a black wire and an
orange wire (+3.3V)? Don't be too concerned if those voltages are off
by 10-20% because that can be normal without a load. Diodes usually
short when they fail (so do transistors, and sometimes you find them on
the outputs, especially the +3.3V) and will cause AC to come out the
rails. I don't know if this will damage the PSU's output filter
capacitors or the mobo, but I'd first try another PSU, initially
without a CPU in the mobo but with the green PSU wire shorted to
ground. Then I'd measure the voltages on the mobo's MOSFETs and
Schottkys because on some of their pins you should find +12V from the
PSU, and on some other pins the CPU core voltage. Stick pieces of
cardboard between the MOSFET and Schottky pins to avoid shorting them
with the meter lead. What PSU do you have? Internally does it look
more like this, heft-wise:

http://static.flickr.com/43/73954319_bc8f9de6d0_o.jpg

or this:

http://static.flickr.com/37/82654518_a55fb37001.jpg