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820-4924-a No Power

C

CRC2018

Member
Little bit of history on this one - customer plugged an external hdd into this one - one of those cheap sata to usb converter box style ones but also plugged in a 5v dc psu to the hdd as well. After which machine is dead - i'm thinking the USB 5V S3 Rail has been back fed with the power from the drive and killed something.

I've checked PP5V_S3 for shorts and found none. I'm not getting any S4 power rails but I am getting PP3V3_S5 and PP5V_S5. PPBUS_G3H is present, green light is on the charger which changes to orange as I would expect.
PM_SLP_S4_L is missing however the prerequisites for it are there. PPVRTC_G3H, RTC_RESET_L, PP3V3_SUS etc.

Anyone know the likely problem given the history?
 
2informaticos

2informaticos

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Trigger SMC_ONOFF_L and check for drop pulse at PM_PWRBTN_L.
If yes, check for pulse at PM_SLP_S4_L too.
 
C

CRC2018

Member
SMC_ONOFF_L is triggerin PM_PWRBTN_L yes. There is a tiny pulse on PM_SLP_S4_L - almost missed it with the meter goes up to 0.023v only that I can see then immediately off again.
 
2informaticos

2informaticos

Administrator
Staff member
That is also 0V, no pulse.
You should be able to catch higher peak (1-2V), if trigger it several times.
An o-scope can catch the peak of any fast pulse...
 
2informaticos

2informaticos

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We cannot ASSUME; need confirmation to go ahead.
Pulse, or not at PM_SLP_S4_L is very important to know exactly.
If present, check the other PM_SLP_Sx_L signals too.

If you trigger SMC_ONOFF_L several times, should be able to catch a higher pulse, on DC voltmeter; if exists, of course.
 
C

CRC2018

Member
Seems like this is another one of apple's idiot boards that won't even attempt to start without the battery plugged in..
With a fully charged new battery the system is pulsing on the PM_SLP_Sx_L signals and actually goes into S0 state. CPU doesn't appear to be heating up though but I do have PP5V_S0 and PPVCC_S0_CPU_PH1 is reading between 1v and 1.3v. not seeing anything on the display at all. I hope this information helps narrow this down a bit further and if you want me to measure anything else let me know!
 
2informaticos

2informaticos

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Staff member
A recent thread about 4924 reports same issue about NO start w/o battery present.
However, I didn't face with this problem yet myself...

Do you get stable voltage at C1301?
PLT_RESET_L comes high?
Did you test for USB activity?
 
C

CRC2018

Member
No C1301 on this board - if you mean C1001 - getting a solid 0v from there. PLT_RESET_L is staying low 0v. USB Mouse lights up. Also appear to be getting some heat from Q7180 and L7130 - they are not excessively hot but warmer than the rest of board.
 
2informaticos

2informaticos

Administrator
Staff member
"No C1301 on this board"
My error, meant C1031; is on the same rail as C1001 too.
If no VCORE, then board doesn't really boot.

You've said before to get 1-1.3V on VCORE...
 
C

CRC2018

Member
Was getting vcore yesterday yes - not today it seems!
Double checked it again no vcore!
It is still getting to S0 as getting PP5V_S0 still at a stable 5V
 
C

CRC2018

Member
u1950:
pin 5 - 3.4v
pin 6 - 3.4v
pin 7 - 3.4v

Is it possible dead U7200? I see it gets power from PP5V_S0 which i'm sure has been backfed from the hard drive customer plugged in?

Edit - I think dead CPU actually VCORE is reading 1ohm to Ground
 
Last edited:
2informaticos

2informaticos

Administrator
Staff member
1 ohm is short; usually 10-15 normal for this board, depending by CPU type.
Just in case, lift the coils and check if short is on the CPU side; 99% yes :(
 
C

CRC2018

Member
Coils removed - short still there, dead CPU it seems shame. Macbook's have to be the first laptops i've worked on where a dodgy USB device can kill the processor - very good circuit design there!
 
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