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Mainboard troubleshooting


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#1 joshmurray

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Posted 23 March 2011 - 09:35 AM

I need some help with a motherboard issue. My desktop would not power on (adsolutely no power) I replaced the power supply and still no power. I connected the 20-pin ATX connector to the motherboard and removed the 4-pin connector from the motherboard. After doing so the computer seems to power up but no display or beep code. The system fan and CPU fan run but no other components work. What can I do? There has to be a way to peplace a capacitor or bypass some part of the mothrboard to restore power. Any advice? It is a MSI and the website gives a few steps but nothing too complex.

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#2 Baltboy

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Posted 23 March 2011 - 11:11 AM

First if you don't have power to the four pin it will never start up since that supplies critical voltage needed to the CPU. As far as trouble shooting the first thing I would do would be to inspect the board for bad capacitors. They should be totally flat on top and a uniform color. If they are bulging upward or if it looks like they are brown near the seams then they are bad and need to be replaced. Other than that the only other thing you can do is verifg that the CPU and memory are still good by testing them in a different known working motherboard.

Edited by Baltboy, 23 March 2011 - 11:12 AM.

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#3 joshmurray

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Posted 23 March 2011 - 11:51 AM

Thanks for the tips. To me it is so strange that with the 4-pin connector attached the fans do not function, but with the 4-pin disconnected all fans function. Do you know of anyway I can test components with a multimeter to verify if they are good or bad?

#4 Platypus

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Posted 24 March 2011 - 05:40 AM

With the behavior you're observing, there could be a short circuit on the motherboard side of the 4-pin connector, preventing power-up when it's connected. You could check for indications of this with a multimeter. With the 4-pin lead disconnected (and not connected to the mains of course), measuring from one of the motherboard socket pins the black wires connect to across to one of the ones the yellow wires go to should measure quite high in resistance. (Either "black" pin to either "yellow" pin.) Depending on the exact design of the circuitry, several kilo-ohms upwards - if a continuous low resistance is shown, e.g. zero, a few ohms or tens of ohms, that would indicate a component in the core voltage switching regulator is shorted or leaky. That would most likely be a surface mounted Mosfet or diode, rather than something like an electrolytic capacitor, so not readily repaired. Such a fault could also damage the CPU unfortunately.

Edited by Platypus, 24 March 2011 - 05:41 AM.

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