Hi everyone!
This is my first post here, I hope to solve this problem with your help. This is my first experience on this type of repair, so forgive me if I make some stupid mistakes.
I have an A1261 17" MacBook Pro (820-2262-A) which has intermittent green light on MagSafe, and when the light flashed I can hear a click coming from the motherboard. The machine would not power on either via the MagSafe of via a known good, fully charged battery. SMC bypass does nothing.
I checked some voltages and got a regular PP3V42_G3H (3.42 volts), a fluctuating PP18V5_DCIN (between 14 and 16 volts) and no PPBUS_G3H. Time to check for shorts.
I initially found a short to ground on PPBUS_G3H, even at J6990 (discovered at Q5315), and started going backwards.
I checked at U7950 and that was ok, I then checked at U5715 and found that pin 3 and 4 of U5715 were shorted to ground, thus shorting PPBUS_G3H via XW7904.
I traced the short back through R7904 and R7906 and found that pin 21 and 22 (CHGR_CSO_P and CHGR_CSO_N) on U7900 are shorted to ground, thus shorting everything connected to them.
Removing R7904 and R7906 (the two shorted rails are interconnected via C7902) eliminates the short on PPBUS_G3H and on pin 3 and 4 of U5715.
Could U7900 be dead and internally shorted to ground? Should I remove it and check if I get no short (not the easy way) or try injecting voltage in some component? Any known bad component that may cause this?
Thank you!
This is my first post here, I hope to solve this problem with your help. This is my first experience on this type of repair, so forgive me if I make some stupid mistakes.
I have an A1261 17" MacBook Pro (820-2262-A) which has intermittent green light on MagSafe, and when the light flashed I can hear a click coming from the motherboard. The machine would not power on either via the MagSafe of via a known good, fully charged battery. SMC bypass does nothing.
I checked some voltages and got a regular PP3V42_G3H (3.42 volts), a fluctuating PP18V5_DCIN (between 14 and 16 volts) and no PPBUS_G3H. Time to check for shorts.
I initially found a short to ground on PPBUS_G3H, even at J6990 (discovered at Q5315), and started going backwards.
I checked at U7950 and that was ok, I then checked at U5715 and found that pin 3 and 4 of U5715 were shorted to ground, thus shorting PPBUS_G3H via XW7904.
I traced the short back through R7904 and R7906 and found that pin 21 and 22 (CHGR_CSO_P and CHGR_CSO_N) on U7900 are shorted to ground, thus shorting everything connected to them.
Removing R7904 and R7906 (the two shorted rails are interconnected via C7902) eliminates the short on PPBUS_G3H and on pin 3 and 4 of U5715.
Could U7900 be dead and internally shorted to ground? Should I remove it and check if I get no short (not the easy way) or try injecting voltage in some component? Any known bad component that may cause this?
Thank you!
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