Asus Crosshair IV Formula - no boot, no post, not powering up...

[adamrzymski]

Hi All.

I just found this great forum using google, and I see i can maybe get some help with my mobo. But from begining...

This mobo was working fine for about 9 months and suddenly stopped to power up.

All other components including PSU are working fine on other motherboard.

After plugin in everything on for bench test I can say that:
All LEDs on mobo buttons are flashing like they should. I believe they are powered from 5V stand by. When I try to power up nothing happens at all no beeps no fan spinning...

After I decided to try forcing PSU to start by shortening PS on to GND. Fans started to spin, CPU diagnostic LED is flashing and HDD LED is flashing, all stays cold and nothing happens. I started to check voltages on diagnostic points. I discovered that for example NB voltage has 0V... I know also that MOBO is missing 3.3V for example where battery for CMOS is there is about 0.5V. Doing more investigation Im at the point of finding that one of Mosfets A09N03 marked on mobo as PQ501 (I need some identification exactly what Mosfet is that, what manufacturer... picture in attachment) is connected to 3.3V from PSU, but on output there is 0V, this output is connected also probably to 3 capacitors which look like are shorted after checking them with multimeter, or there is some other circuit shorted connected to them - I cant verify that in this stage without desoldering them. All voltages on PSU socket are fine. Another picture included with explanation and location of A09N03. I have theory that this caps are shorted, and this caused damage of this MOSFET, which now is not giving any output voltage. Any advises or ideas what further I can check? I dont want to desolder anythin ATM as there is a small chance of posting this MOBO to ASUS for warranty service, the problem is that mobo was a gift, I dont have any reciepe and no idea where it was bought. ASUS told me to return it to retailer, but I have no more contact with person that gave me that gift, so I dont even know which retailer. I live in Uk and Im trying to get some support from ASUS uk distributor, maybe they will RMA this mobo for me. Has anyone have any similiar experience with this mobo? or you have any idea what I can test more, please respond in this topic.

[Nilendra]

my mother board is same as this. I pressed the cmos clear button after that key board is not functioning. I checked with both ps2 and usb keyboards but the same error came if any one can help me please reply.

[Uranium-235]

use the warranty, I bet there is more than a 1yr warranty for those

[rilski]

If you are going to DIY for the heck of it, and if somehow warranty isn't a concern, then I would just replace the "shorted" capacitors.

Also, check the voltage regulators for shorts or if it is in working condition.

Check all of your PC components if they are working just to be sure, it doesn't have to be all of them. Just the essentials, CPU/RAM/MEMORY/VGA.

[DJComy]

Originally Posted by adamrzymski

Hi All.

I just found this great forum using google, and I see i can maybe get some help with my mobo. But from begining...

This mobo was working fine for about 9 months and suddenly stopped to power up.

All other components including PSU are working fine on other motherboard.

After plugin in everything on for bench test I can say that:
All LEDs on mobo buttons are flashing like they should. I believe they are powered from 5V stand by. When I try to power up nothing happens at all no beeps no fan spinning...

After I decided to try forcing PSU to start by shortening PS on to GND. Fans started to spin, CPU diagnostic LED is flashing and HDD LED is flashing, all stays cold and nothing happens. I started to check voltages on diagnostic points. I discovered that for example NB voltage has 0V... I know also that MOBO is missing 3.3V for example where battery for CMOS is there is about 0.5V. Doing more investigation Im at the point of finding that one of Mosfets A09N03 marked on mobo as PQ501 (I need some identification exactly what Mosfet is that, what manufacturer... picture in attachment) is connected to 3.3V from PSU, but on output there is 0V, this output is connected also probably to 3 capacitors which look like are shorted after checking them with multimeter, or there is some other circuit shorted connected to them - I cant verify that in this stage without desoldering them. All voltages on PSU socket are fine. Another picture included with explanation and location of A09N03. I have theory that this caps are shorted, and this caused damage of this MOSFET, which now is not giving any output voltage. Any advises or ideas what further I can check? I dont want to desolder anythin ATM as there is a small chance of posting this MOBO to ASUS for warranty service, the problem is that mobo was a gift, I dont have any reciepe and no idea where it was bought. ASUS told me to return it to retailer, but I have no more contact with person that gave me that gift, so I dont even know which retailer. I live in Uk and Im trying to get some support from ASUS uk distributor, maybe they will RMA this mobo for me. Has anyone have any similiar experience with this mobo? or you have any idea what I can test more, please respond in this topic.

HI, did U fix your motherboard, what seems to be a problem...!? Mine is acting kinda similar. Same LED lights are on, and won't boot up normaly, unless i do a short circuit on green and black wire on my PCU.

[DJComy]

I found datasheet of A09N03... Can U tell me did U manage your mobo to work?

[momaka]

With a multimeter, measure the resistance between Source (the right-most lead on the MOSFET) and Drain (the big tab on the MOSFET). If you have a manual multimeter, use the lowest resistance setting. Let me know what you get. Also, if you can post some more (and better) pictures of the area where that MOSFET is, that would be great. This may or may not be a bucking circuit. If it's a bucking circuit, the Drain on one of the nearby MOSFETs may be connected to the Source of this MOSFET and the Source on that MOSFET will be connected to ground. If that's the case, then it's possible that that MOSFET may have shorted out. But again, only good pictures can help to see what the circuit is supposed to be.