Hello there,
I'm trying to fix a mistake, very likely mine, whose consequence seems to be an unstable 5V rail, on a 820-3332-A logic board.
Context:
Initially, I had no image on both the external display and the laptop screen; since PPVCORE_GPU and PPVCORE_S0_GFX_REG were 0V, I applied some flux on the U8900 and used the soldering iron to make the joints look better. It worked and I could get an image. However, when booting, the process systematically get stuck at the end of the loading bar, with the Apple logo. I rebooted, ran the AHT, and noticed that the screen - which should be blue - was actually full of blue artefacts. Being unsure about the cause (faulty GPU or the quick-and-dirty-temporarily-fix applied), I took the logical board out of the mac again, removed the U8900, cleaned the surface properly, and soldered everything back in place.
Eventually, I put the logical board back in place, but it is now unable to boot.
Six points that might be worth to mention, regarding the above process:
1) When trying to remove the U8900 with the hot air soldering station, temp was 370°C. I made several attempts, stopping after 40-50sec,it was not working
2) After a break, I started again at 420°C. U8900 left the the board after 5sec
3) During the whole process, all the elements around the U8900 were below 2 layers of Kapton tape.
4) I did not remove the thermal heatsink
5) The U8900 chip ended stuck on the MagSafe connector before I soldered it back in place. Dunno if there is a risk for these chips to be "erased" by magnets (?)
6) The AHT displayed an error, but at that point it was very likely irrelevant (4hdd/11/40000000:sata(0,0))
Current situation:
Everytime I plug the magsafe connector on the board (outside the laptop) the light of the charger is green for a second, then turns amber.
Fans start spinning for 1.5sec, then stop.
Then they start spinning again for 1.5 sec, before stopping again.
It looks like the process could almost start a third time, but doesnt. We can hear a "tick".
Then, nothing.
PP3V42_G3H is OK ; C6999 pin 1 shows 3.45V, as L6995, R7941, L6754, C7002, U7000 pin 12, etc
PP3V3_S5_SMC is OK: L4901, pin 2 shows 3.44V
On U7201:
P3V3S5_EN, pin 21: 3.44V
P3V3S5_PGOOD, pin 20: 3.41V
P5VS5_EN, pin 12: 3.44V
P5VS4_EN, pin4: 0V
P5VS4_PGOOD, pin5: 0V
I checked a few more rails;
P5V0S0_SS @0V for 4sec, then 0.3V, when measured on pin4 of Q7860
PP5V_S0 @0.26V/0.27V then 4.67/5V, then 0.26V again. It is never stable for more than a second
PP5V_S4, on C7861, pin1 :1.27V, then 5.08V then 1.27 again
pin2 shows 0, then 0.27V
P5VS0_EN, pin 3 on Q7865, shows 0V for 4 sec, then 0.3V,
R7978is okish, 99.8Ohms,
Im on the page presenting the Mobile System Power State Table, the S5 Rail Enables & PGOOD, S0 Rail PGOOD Circuitry, etc but I think there is maybe an issue with the PM_SLP_S3_L.
What should I check next? Any suggestion is welcome.
I'm trying to fix a mistake, very likely mine, whose consequence seems to be an unstable 5V rail, on a 820-3332-A logic board.
Context:
Initially, I had no image on both the external display and the laptop screen; since PPVCORE_GPU and PPVCORE_S0_GFX_REG were 0V, I applied some flux on the U8900 and used the soldering iron to make the joints look better. It worked and I could get an image. However, when booting, the process systematically get stuck at the end of the loading bar, with the Apple logo. I rebooted, ran the AHT, and noticed that the screen - which should be blue - was actually full of blue artefacts. Being unsure about the cause (faulty GPU or the quick-and-dirty-temporarily-fix applied), I took the logical board out of the mac again, removed the U8900, cleaned the surface properly, and soldered everything back in place.
Eventually, I put the logical board back in place, but it is now unable to boot.
Six points that might be worth to mention, regarding the above process:
1) When trying to remove the U8900 with the hot air soldering station, temp was 370°C. I made several attempts, stopping after 40-50sec,it was not working
2) After a break, I started again at 420°C. U8900 left the the board after 5sec
3) During the whole process, all the elements around the U8900 were below 2 layers of Kapton tape.
4) I did not remove the thermal heatsink
5) The U8900 chip ended stuck on the MagSafe connector before I soldered it back in place. Dunno if there is a risk for these chips to be "erased" by magnets (?)
6) The AHT displayed an error, but at that point it was very likely irrelevant (4hdd/11/40000000:sata(0,0))
Current situation:
Everytime I plug the magsafe connector on the board (outside the laptop) the light of the charger is green for a second, then turns amber.
Fans start spinning for 1.5sec, then stop.
Then they start spinning again for 1.5 sec, before stopping again.
It looks like the process could almost start a third time, but doesnt. We can hear a "tick".
Then, nothing.
PP3V42_G3H is OK ; C6999 pin 1 shows 3.45V, as L6995, R7941, L6754, C7002, U7000 pin 12, etc
PP3V3_S5_SMC is OK: L4901, pin 2 shows 3.44V
On U7201:
P3V3S5_EN, pin 21: 3.44V
P3V3S5_PGOOD, pin 20: 3.41V
P5VS5_EN, pin 12: 3.44V
P5VS4_EN, pin4: 0V
P5VS4_PGOOD, pin5: 0V
I checked a few more rails;
P5V0S0_SS @0V for 4sec, then 0.3V, when measured on pin4 of Q7860
PP5V_S0 @0.26V/0.27V then 4.67/5V, then 0.26V again. It is never stable for more than a second
PP5V_S4, on C7861, pin1 :1.27V, then 5.08V then 1.27 again
pin2 shows 0, then 0.27V
P5VS0_EN, pin 3 on Q7865, shows 0V for 4 sec, then 0.3V,
R7978is okish, 99.8Ohms,
Im on the page presenting the Mobile System Power State Table, the S5 Rail Enables & PGOOD, S0 Rail PGOOD Circuitry, etc but I think there is maybe an issue with the PM_SLP_S3_L.
What should I check next? Any suggestion is welcome.
Last edited:
