Gigabyte GA-H81M-s2pv Dead PCH ??
Good day folks, or I should say Merry Christmas, since it's right around the corner 
Still, work never stops around here, so here's something which I haven't done very often in the past and I'd like to try my hand at since the occasion came up and that is to troubleshoot a desktop motherboard. Usually these are not worth saving, but this one came with decent RAM and the CPU, so it's worth a shot, plus I'm not charging for it, since it's technically mine at this point and I'm not under any pressure.
The thing is.....dead....dead as a doornail in fact: absolutely no power at all and I think the PCH is dead, so beyond repair. The first sign that something's very wrong is the purple 5VSB wire of the PSU only reads 2.5v when the ATX connector is plugged into the board. The PCH (pictured with the HS removed) then starts to get rather hot and the D-PAK MOSFET labeled Q61 to the bottom-right of the PCH is even worse ! I concentrated on that area and started taking some measurements with my multimeter in diode mode. What I found so far is pretty contradictory:
-the FET itself seems to be good
-the two electrolytic capacitors visible in the close-up are connected together and they read a dead-short to GND (between their legs on the back). This is most likely where the PCH's power rail is. Ok, makes sense so far.
-there's two BIOS chips there too. This is where it starts to get confusing: pin 8 of both chips, which is VCC, seems to be tied to the same power rail as those two caps where the short it, BUT if I apply 3v directly to the BIOS chip with my power supply, the current draw is pretty low: 0.14A (though it could still be considered too high, considering it's not doing anything at that point !). Still, if I then try to apply voltage to the caps, I suddenly pull a much higher current, maxing out my small PSU at 2A....so how does this work ? It's almost like there's something else sitting between the PCH's power rail (where the caps are) and the power rail where the ICs are. My idea is that the PCH is on a sub-rail and it's that FETs body diode that causes power to flow in one direction, but not in the other, so when I apply power straight on the chips, the FET is keeping that power from reaching the PCH where my short is. Still, this doesn't explain why my meters shows them as one single rail...I should at least see a diode drop between the caps and the ICs, but all I get is a very small reading, like 0.014v in diode mode...not sure what to think of this. Unfortunately, it doesn't seem fixable, but decided to share it with you nonetheless, maybe someone has a brainy idea or even a boardview by some freak chance. Thank you.
Still, work never stops around here, so here's something which I haven't done very often in the past and I'd like to try my hand at since the occasion came up and that is to troubleshoot a desktop motherboard. Usually these are not worth saving, but this one came with decent RAM and the CPU, so it's worth a shot, plus I'm not charging for it, since it's technically mine at this point and I'm not under any pressure.The thing is.....dead....dead as a doornail in fact: absolutely no power at all and I think the PCH is dead, so beyond repair. The first sign that something's very wrong is the purple 5VSB wire of the PSU only reads 2.5v when the ATX connector is plugged into the board. The PCH (pictured with the HS removed) then starts to get rather hot and the D-PAK MOSFET labeled Q61 to the bottom-right of the PCH is even worse ! I concentrated on that area and started taking some measurements with my multimeter in diode mode. What I found so far is pretty contradictory:
-the FET itself seems to be good
-the two electrolytic capacitors visible in the close-up are connected together and they read a dead-short to GND (between their legs on the back). This is most likely where the PCH's power rail is. Ok, makes sense so far.
-there's two BIOS chips there too. This is where it starts to get confusing: pin 8 of both chips, which is VCC, seems to be tied to the same power rail as those two caps where the short it, BUT if I apply 3v directly to the BIOS chip with my power supply, the current draw is pretty low: 0.14A (though it could still be considered too high, considering it's not doing anything at that point !). Still, if I then try to apply voltage to the caps, I suddenly pull a much higher current, maxing out my small PSU at 2A....so how does this work ? It's almost like there's something else sitting between the PCH's power rail (where the caps are) and the power rail where the ICs are. My idea is that the PCH is on a sub-rail and it's that FETs body diode that causes power to flow in one direction, but not in the other, so when I apply power straight on the chips, the FET is keeping that power from reaching the PCH where my short is. Still, this doesn't explain why my meters shows them as one single rail...I should at least see a diode drop between the caps and the ICs, but all I get is a very small reading, like 0.014v in diode mode...not sure what to think of this. Unfortunately, it doesn't seem fixable, but decided to share it with you nonetheless, maybe someone has a brainy idea or even a boardview by some freak chance. Thank you.
Attached Files
