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P5BW-LA motherboard diagram

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  • Motherboards
  • Power Supplies
Last response: in Motherboards
November 26, 2010 5:38:13 PM

I seem to have no power at all to the system. Everything was fine yesterday and today , you push the startup button and nothing happens. I've checked the power supply with a power supply tester (Coolmax) and it looks OK. Are there fuses on motherboards? Where can you get a schematic? Thanks for any help.

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a c 156 V Motherboard
a c 144 ) Power supply
November 26, 2010 7:37:04 PM

The problem with power supply testers is that they can tell you if a PSU is bad, but they cannot tell you if one is good. They do not put enough of a load on the PSU.

Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.
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November 27, 2010 4:38:04 AM

jsc said:
The problem with power supply testers is that they can tell you if a PSU is bad, but they cannot tell you if one is good. They do not put enough of a load on the PSU.

Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.



I jumpered the green to the black and the PSU comes on. I'm also powering the HD. I plugged the power back into the MOBO with the jumper on and the system comes up. It then says the System fan has failed and to service the PC. The CPU fan is fine, however I replaced it, just to make sure. No effect.
Is the system fan and the CPU fan the same?
I can go into the BIOS setup. Any further suggestions?
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a b V Motherboard
a b ) Power supply
November 27, 2010 9:13:18 AM

Look in the BIOS and tell us all the temperatures. You have a brand PC like HP? Is te case fan spinning and connected to the motherboard or it's connected to the PSU?
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November 28, 2010 2:02:02 AM

mosox said:
Look in the BIOS and tell us all the temperatures. You have a brand PC like HP? Is te case fan spinning and connected to the motherboard or it's connected to the PSU?


My system is an HP Media Center PC m7674n. I looked at the case and found that there was a system fan that I had not connected. I connected it. If I pull the AXTPWR connector and short the green to the black, the power supply and the hard drive come on. I can then plug in the connector and the system comes on. When it tries to boot the windows screen stsrts to appear then stops and goes back to the startup screen. If I pull the jumper out, everything goes down. I read in one discussion that this would indicate a problem in the startup system of the motherboard.
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a b V Motherboard
a b ) Power supply
November 28, 2010 8:58:45 AM

Did you edit the title, it was something about a system fan alert or that was some other thread? If yes, address the issue to the HP, this is a very specific issue related to their systems. Go in the BIOS and see if you can disable the system fan warning or try with some other case fan.

http://h10025.www1.hp.com/ewfrf/wc/product?product=3271...
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November 29, 2010 1:46:55 PM

mosox said:
Did you edit the title, it was something about a system fan alert or that was some other thread? If yes, address the issue to the HP, this is a very specific issue related to their systems. Go in the BIOS and see if you can disable the system fan warning or try with some other case fan.

http://h10025.www1.hp.com/ewfrf/wc/product?product=3271...



I have the unit breadboarded and I found another 'system ' fan in the cabinet. I connected it and that part of the problem went away. I still have to jumper to get the unit running and my harddrive seems corrupted. I'm trying to set up a new harddrive to boot from and then retrieve my data from the old hard drive. Having a little trouble with the Seagate utility program to format the harddrive. Really appreciate your help.
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December 4, 2010 2:34:48 AM

The problem turned out to be the power supply. Something in the switch circuit. I put a new power supply in and all the original parts and it works fine. Thanks for everyones help.
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December 7, 2010 2:45:10 PM

Best answer selected by reggie62.
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a c 136 V Motherboard
a b ) Power supply
December 8, 2010 7:33:50 AM

This topic has been closed by Maziar
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