Hi,
I'm new to the forum and would appreciate some help. Hopefully I posted this correctly. I purchased a non-working 2010 15” Mac Book Pro i7-2.66 4GB RAM with a 820-2850-A logic board with the intent of repairing and reselling it. The computer case is in excellent shape with no signs of water damage or corrosion but it does have a cracked LCD screen. This is my first attempt to trying to trouble shoot one of these boards. I read through Rossman's presentation (very useful) and watch many related videos. I have been working on this for days and need some help.
Symptom: Green light on charger, fans spin at low speed, power light comes on front edge. No chime, no display, no USB mouse LED. After a minute, the fans shut down and the system starts again. Does this with or without a battery. Appears system is not making it out of POST.
Found PPVCORE_S0_CPU decoupling cap C1627 was completely missing and decoupling cap C1632 was half off. Perhaps someone accidentally scraped them off when removing the bottom cover. Reattaching the half off cap and replacing the missing cap had no affect but may still be related as will become apparent below.
Powering card on bench results in the following: Green charging light comes on, the fans stay off for 7 seconds, then spin fast for about 1 second and then slow for 15 seconds then fast for 30 seconds. The cycle then repeats. Again, no chime and no USB mouse LED.
All power rails appear to be present and system is entering S0 state.
The only anomaly so far is that PPVCORE_S0_CPU (the same power rail that had the missing caps above) is pulsing about 1/sec, i.e. it is normally 1.08V but pulses down to about 0.8V about 1/sec. The schematic indicates it should be at 1.25V but I got the same 1.08V reading (without pulsing) on another good system. Both phases seem to be working identically.
Pulsing can be traced back to the Gates on Q7410, Q7415, Q7420 and Q7425 and corresponding output pins on U7400 as well as the CPUIMVP_ISEN1N, 1P, 2N and 2P lines.
U7400 V5FILT (pin38) and V5IN (pin26) are 5V and do NOT pulse.
PPBUS_CPU_IMVP_ISNS does NOT pulse and is steady at 10 volts.
U7400 pin 13 PSI input (CPU_PSI_L) from the CPU is pulsing low (0.8V to 0V) at same rate.
PPVCORE_S0_CPU_VCAP0, PPVCORE_S0_CPU_VCAP1 that are sourced by the CPU are also pulsing at 1Hz but PPVCORE_S0_CPU_VCAP2 is not. Can't explain this.
Also, U7400 VID0 - VID 6 (pins 20 - 14 respectively) are also apparently being driven by the CPU but some are also pulsing as follows:
VID 0: normally 0.8 pulses down to 0.0
VID 1: normally 0 pulses up to 0.8
VID 2: normally 0 pulses up to 0.8
VID 3: steady 0
VID 4: normally 0 pulses up to 0.8
VID 5: steady 0.8
VID 6: steady 0.0
I measured all the resistors in the PPVCORE_S0_CPU sensing circuits on page 68 and they match from Phase 1 to Phase 2 and to values on a junk board.
I don't think the CPU is completely dead since CPU_PSI_L and the CPUIMVP_VID0-VID6 signals that come from the CPU are active. If so, it looks like something is wrong with the U7400 PPVCORE_S0_CPU circuitry. I suspect PPVCORE_S0_CPU sensing is triggering every second and then the system shuts down after a minute but I can't figure out what is causing this.
Any suggestions on how to proceed would be greatly appreciated.
Thanks!!!
I'm new to the forum and would appreciate some help. Hopefully I posted this correctly. I purchased a non-working 2010 15” Mac Book Pro i7-2.66 4GB RAM with a 820-2850-A logic board with the intent of repairing and reselling it. The computer case is in excellent shape with no signs of water damage or corrosion but it does have a cracked LCD screen. This is my first attempt to trying to trouble shoot one of these boards. I read through Rossman's presentation (very useful) and watch many related videos. I have been working on this for days and need some help.
Symptom: Green light on charger, fans spin at low speed, power light comes on front edge. No chime, no display, no USB mouse LED. After a minute, the fans shut down and the system starts again. Does this with or without a battery. Appears system is not making it out of POST.
Found PPVCORE_S0_CPU decoupling cap C1627 was completely missing and decoupling cap C1632 was half off. Perhaps someone accidentally scraped them off when removing the bottom cover. Reattaching the half off cap and replacing the missing cap had no affect but may still be related as will become apparent below.
Powering card on bench results in the following: Green charging light comes on, the fans stay off for 7 seconds, then spin fast for about 1 second and then slow for 15 seconds then fast for 30 seconds. The cycle then repeats. Again, no chime and no USB mouse LED.
All power rails appear to be present and system is entering S0 state.
The only anomaly so far is that PPVCORE_S0_CPU (the same power rail that had the missing caps above) is pulsing about 1/sec, i.e. it is normally 1.08V but pulses down to about 0.8V about 1/sec. The schematic indicates it should be at 1.25V but I got the same 1.08V reading (without pulsing) on another good system. Both phases seem to be working identically.
Pulsing can be traced back to the Gates on Q7410, Q7415, Q7420 and Q7425 and corresponding output pins on U7400 as well as the CPUIMVP_ISEN1N, 1P, 2N and 2P lines.
U7400 V5FILT (pin38) and V5IN (pin26) are 5V and do NOT pulse.
PPBUS_CPU_IMVP_ISNS does NOT pulse and is steady at 10 volts.
U7400 pin 13 PSI input (CPU_PSI_L) from the CPU is pulsing low (0.8V to 0V) at same rate.
PPVCORE_S0_CPU_VCAP0, PPVCORE_S0_CPU_VCAP1 that are sourced by the CPU are also pulsing at 1Hz but PPVCORE_S0_CPU_VCAP2 is not. Can't explain this.
Also, U7400 VID0 - VID 6 (pins 20 - 14 respectively) are also apparently being driven by the CPU but some are also pulsing as follows:
VID 0: normally 0.8 pulses down to 0.0
VID 1: normally 0 pulses up to 0.8
VID 2: normally 0 pulses up to 0.8
VID 3: steady 0
VID 4: normally 0 pulses up to 0.8
VID 5: steady 0.8
VID 6: steady 0.0
I measured all the resistors in the PPVCORE_S0_CPU sensing circuits on page 68 and they match from Phase 1 to Phase 2 and to values on a junk board.
I don't think the CPU is completely dead since CPU_PSI_L and the CPUIMVP_VID0-VID6 signals that come from the CPU are active. If so, it looks like something is wrong with the U7400 PPVCORE_S0_CPU circuitry. I suspect PPVCORE_S0_CPU sensing is triggering every second and then the system shuts down after a minute but I can't figure out what is causing this.
Any suggestions on how to proceed would be greatly appreciated.
Thanks!!!
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