Mosfets get hot and there is a lot of current moving through them so it doesn't take much for there to be some run away effect when they fail and burn when there has been a short. Keeping them cool isn't just for looks but to keep boards from failing and it is something everyone should do especially when of if one doesn't have the skills or the tools to do such repairs. On some boards including vintage get ferociously hot and any attempt to manage the heat will do some good.

nforce4max wrote:

Mosfets get hot and there is a lot of current moving through them so it doesn't take much for there to be some run away effect when they fail and burn when there has been a short. Keeping them cool isn't just for looks but to keep boards from failing and it is something everyone should do especially when of if one doesn't have the skills or the tools to do such repairs. On some boards including vintage get ferociously hot and any attempt to manage the heat will do some good.

Do you know what could have caused to burn when i just turned it on. I mean like maybe the PSU is faulty, the power board i am using, the motherboard, etc. Also do you think i can solder a new mosfet chip on the motherboard. or is the board ready for the scrap yeard?

short somewhere. drew too much current.

BloodyCactus wrote:

short somewhere. drew too much current.

can you give me some ideas of where the short would have occurred. Sorry i have no idea about the technical details of how hardware works. I am just very curious what would have caused, would age of the component be considered a factor?

JaKSLaP wrote:

BloodyCactus wrote:

short somewhere. drew too much current.

can you give me some ideas of where the short would have occurred. Sorry i have no idea about the technical details of how hardware works. I am just very curious what would have caused, would age of the component be considered a factor?

Wave a magical wand and the board appears but there is no answer to be found, the board goes away.... Shorts happen and you can do some google and it won't take long before you get the idea just how complex multi layer printed circuit boards can be. It literally can be anywhere on the board but it is common for it to occur in the mosfet itself before it had failed. It might work after a repair but I wouldn't bet on it as such a failure on a modern board is lethal especially on lga 2011 builds.

nforce4max wrote:

JaKSLaP wrote:

BloodyCactus wrote:

short somewhere. drew too much current.

can you give me some ideas of where the short would have occurred. Sorry i have no idea about the technical details of how hardware works. I am just very curious what would have caused, would age of the component be considered a factor?

Wave a magical wand and the board appears but there is no answer to be found, the board goes away.... Shorts happen and you can do some google and it won't take long before you get the idea just how complex multi layer printed circuit boards can be. It literally can be anywhere on the board but it is common for it to occur in the mosfet itself before it had failed. It might work after a repair but I wouldn't bet on it as such a failure on a modern board is lethal especially on lga 2011 builds.

ok Thank you. the board is a LGA775, i gonna try and replaced the mosfet and see how i will go

Replace the Mosfet but check for shorts everywhere obvious before powering up.

Imperious wrote:

Replace the Mosfet but check for shorts everywhere obvious before powering up.

when you say check for shorts. What exactly do you mean, what will i be looking for.

JaKSLaP wrote:

Imperious wrote:

Replace the Mosfet but check for shorts everywhere obvious before powering up.

when you say check for shorts. What exactly do you mean, what will i be looking for.

For starters on the Mosfets themselves, there shouldn't be a short circuit (0-10ohms) across any pins. Make sure +5v and +12v aren't
shorted to ground as well.

look for any burn spots on the board, where excessive heat might have been. possible the mosfet just died or got stuck in an open/close or sat too long in the 'in between' time. mosfets dont like being in the gray area between open+close.

BloodyCactus wrote:

look for any burn spots on the board, where excessive heat might have been. possible the mosfet just died or got stuck in an open/close or sat too long in the 'in between' time. mosfets dont like being in the gray area between open+close.

What do you mean by Open/Close, sorry i am just trying to fully understand the situation so i can avoid it in the future.

a mosfet is a switch. you can get p or n channel ones. (ones that basically work with +ve or -ve/gnd voltages). the danger zone for a mosfet is between open state + close state. its neither open and neither closed. mosfets are sensitive to esd too. many things can kill a mosfet.

To expand on this, most transistors in digital systems operate in switch mode. They will be either fully on or fully off.

For this transistor:
http://www.onsemi.com/pub_link/Collateral/MTB50P03HDL-D.PDF

Transistors operating in a fully on state are generally considered to be operating in saturation. They are passing as much current through as they are capable of. For a MOSFET, saturation is achieved by providing a high gate voltage.

The figure of merit is figure 4. Resistance between drain and source (exit and entrance) is about 30% higher with less gate voltage, which translates into approximately 60% greater power emitted by the MOSFET for any given current.