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[SOLVED]820-2936 green light no power no fan
- Thread starter djpat1974
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I am going to oversimplify. 99% of the time, this will be one of four things.
1) PP3V3_S5 is shorted to ground.
2) The IC responsible for creating PP3V3_S5 is not receiving power on its VIN/VCC/VDD/voltage input pin.
3) The IC responsible for creating PP3V3_S5 is bad.
4) The IC responsible for creating PP3V3_S5 is not being told to create PP3V3_S5.
TPS51125 is an electronic chip, and like all electronic chips, to do something it wants power. What feeds it power? Datasheet says it gets power to do what it does on the VIN pin. VIN, as in, voltage in, as in, power going into it so it can turn on is provided on pin 16. Is pin 16 is getting 12.56v? If not, figure that out.
Looking at the page, on the side where PP3V3_S5 is created, we have a pin called "P3V3S5_ENTRIP"... let's guess. P3V3S5 is the name of the rail we are missing. Let's guess what ENTRIP stands for. This means that the chip itself will natrually always create PP3V3_S5, UNLESS you short this pin to ground.
This is the opposite of chips like U9701 on this board. With U9701, you send 3v to the enable pin A3 to turn it on. With U7200, voltage is already present at its enable pin, internally, inside the chip. U9701 is by default off, and must be enabled to turn on. U7200 is by default on, and must be "disabled" to turn off.
So in order for PP3V3_S5 to be turned on, voltage must be allowed to be present at pin 6 of U7200. Look at Q7221. What does it do? On pins 3 and 4, ,we have a path where P3V3S5_ENTRIP(which must be present for PP3V3_S5 to turn on) can go straight to ground. What type of transistor is Q7221? If we google SSM6N37FEAPE, we see it is an N channel MOSFET, meaning the voltage on the gate must be higher than the voltage on the source for it to turn on.
So, if P3V3S5_EN_L is present, it will send P3V3S5_ENTRIP from U7200 to ground, and we won't get anything on PP3V3_S5. Note the _L, and the _EN. This is telling. P3V3S5 is our rail - EN means enable, and _L means while low. So, when that signal is LOW, as in 0v, Q7221 will not send P3V3S5_ENTRIP to ground, and PP3V3_S5 will be allowed to turn on. So we need P3V3S5_EN_L to be low. Where does this come from?
P3V3S5_EN.. as in, ENable PP3V3_S5. According to your measurements, we have 3.4v there - so the IC responsible for creating PP3V3_S5 is being told to turn on. This crosses out #4 as a possible problem.
P3V3S5_EN_L comes from U7941. U7941 takes SMC_PM_G2_EN and turns it into P5V3V3_REG_EN at 3.3v, and then INVERTS it(note the triangle with a dot on it) to 0v for P3V3S5_EN_L. So, if you are getting SMC_PM_G2_EN, which you are, you're at the first step needed for success. Second step will be, is U7941 keeping P3V3S5_EN_L low? If it is, it is doing its job - move on. If not, replace U7941.
If P3V3S5_EN_L is low, move on. Does U7200 have voltage present on its entrip pin at pin 6 for PP3V3S5_ENTRIP? If yes, then check for short to ground on PP3V3_S5. If no short to ground, then we have to imagine that U7200 is dead. Replace U7200.
If P3V3S5_EN_L is low, but pin 6 of U7200 is also low, then we must explore why this is. Either U7200 is dead, or Q7221 is malfunctioning and shorting P3V3S5_ENTRIP to ground regardless of whether P3V3S5_EN_L is present or not. 99% of the time this will be bad U7200, but removing Q7221 can be done quickly to help confirm.
1) PP3V3_S5 is shorted to ground.
2) The IC responsible for creating PP3V3_S5 is not receiving power on its VIN/VCC/VDD/voltage input pin.
3) The IC responsible for creating PP3V3_S5 is bad.
4) The IC responsible for creating PP3V3_S5 is not being told to create PP3V3_S5.
TPS51125 is an electronic chip, and like all electronic chips, to do something it wants power. What feeds it power? Datasheet says it gets power to do what it does on the VIN pin. VIN, as in, voltage in, as in, power going into it so it can turn on is provided on pin 16. Is pin 16 is getting 12.56v? If not, figure that out.
Looking at the page, on the side where PP3V3_S5 is created, we have a pin called "P3V3S5_ENTRIP"... let's guess. P3V3S5 is the name of the rail we are missing. Let's guess what ENTRIP stands for. This means that the chip itself will natrually always create PP3V3_S5, UNLESS you short this pin to ground.
This is the opposite of chips like U9701 on this board. With U9701, you send 3v to the enable pin A3 to turn it on. With U7200, voltage is already present at its enable pin, internally, inside the chip. U9701 is by default off, and must be enabled to turn on. U7200 is by default on, and must be "disabled" to turn off.
So in order for PP3V3_S5 to be turned on, voltage must be allowed to be present at pin 6 of U7200. Look at Q7221. What does it do? On pins 3 and 4, ,we have a path where P3V3S5_ENTRIP(which must be present for PP3V3_S5 to turn on) can go straight to ground. What type of transistor is Q7221? If we google SSM6N37FEAPE, we see it is an N channel MOSFET, meaning the voltage on the gate must be higher than the voltage on the source for it to turn on.
So, if P3V3S5_EN_L is present, it will send P3V3S5_ENTRIP from U7200 to ground, and we won't get anything on PP3V3_S5. Note the _L, and the _EN. This is telling. P3V3S5 is our rail - EN means enable, and _L means while low. So, when that signal is LOW, as in 0v, Q7221 will not send P3V3S5_ENTRIP to ground, and PP3V3_S5 will be allowed to turn on. So we need P3V3S5_EN_L to be low. Where does this come from?
P3V3S5_EN.. as in, ENable PP3V3_S5. According to your measurements, we have 3.4v there - so the IC responsible for creating PP3V3_S5 is being told to turn on. This crosses out #4 as a possible problem.
P3V3S5_EN_L comes from U7941. U7941 takes SMC_PM_G2_EN and turns it into P5V3V3_REG_EN at 3.3v, and then INVERTS it(note the triangle with a dot on it) to 0v for P3V3S5_EN_L. So, if you are getting SMC_PM_G2_EN, which you are, you're at the first step needed for success. Second step will be, is U7941 keeping P3V3S5_EN_L low? If it is, it is doing its job - move on. If not, replace U7941.
If P3V3S5_EN_L is low, move on. Does U7200 have voltage present on its entrip pin at pin 6 for PP3V3S5_ENTRIP? If yes, then check for short to ground on PP3V3_S5. If no short to ground, then we have to imagine that U7200 is dead. Replace U7200.
If P3V3S5_EN_L is low, but pin 6 of U7200 is also low, then we must explore why this is. Either U7200 is dead, or Q7221 is malfunctioning and shorting P3V3S5_ENTRIP to ground regardless of whether P3V3S5_EN_L is present or not. 99% of the time this will be bad U7200, but removing Q7221 can be done quickly to help confirm.
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