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820-2262 - no power, no MagSafe light

M

mikiotty

New member
Hi everyone.
I have an A1261 17" MacBook Pro (old, I know) that I'm trying to fix. The board is a 820-2262.
I have no solid MagSafe light: it blinks regularly but very faintly, sometimes green, sometimes orange. You can hear a very light clicking from the board when the light blinks.
I measured all the basic power rails, including PP18V5_DCIN, and they all fluctuate between 0 and the target voltage. Even the OneWire circuit fluctuates.
The charger is an original 85W Apple charger, but I tried a load of different bricks and there's no difference.
No liquid damage, no previous repairs.
I need some advice... thank you!
 
2informaticos

2informaticos

Administrator
Staff member
First of all, welcome to the forum!

If PP18V5_DCIN fluctuates, very likely original charger detects some problem on the ACIN Detection, or Inrush Limiter circuit.
U6900 is the first suspect; Q6950 may have leakage too.

Check if get stable voltages using fake charger, or lab PSU.
 
2informaticos

2informaticos

Administrator
Staff member
Please, write directly on the Reply box, instead of clicking Reply button.
No reason to quote an entire post, visible few centimeters above.
We try to maintain forum aesthetic...
 
M

mikiotty

New member
Right, sorry!
I got a steady green light with a fake charger. Replaced Q6950, got a green light with the Apple charger. Tested rails:

PP18V5_DCIN= 18.38V (at F6900 and Q6950 pin 1-3)
PP18V5_G3H_CHGR= 18.38V (at Q6950 pin 5-8)
PPDCIN_G3H= 17.59V (at C7800)
PP3V42_G3H= 3.33V (at L7810)
PPBUS_G3H= 0,31V (at C7155)

After a while, it got back to the initial status and now I have a short to ground on PPBUS_G3H. Q6950 gets hot (alcohol immediately evaporates on top of it) and charger LED pulses again even with fake charger.
Should I inject some low voltage on PPBUS_G3H and check for heat on components?
 
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2informaticos

2informaticos

Administrator
Staff member
What is the exact ohm resistance to ground at PPBUS_G3H?
Compare the reading with the values from the big coils (to ground).
 
M

mikiotty

New member
Ok, I found the short. It was not on PPBUS_G3H, found by disconnecting L7900 and isolating the short to the CHGR_PHASE side.
Q7902 had shorted itself internally to ground, replacing that allowed the board to turn on and have fanspin. The problem now is that the whole 18.5V from the charger is passed to PPBUS_G3H, so other than fan activity (at full blast), there is not much else.
 
M

mikiotty

New member
Ok now it doesn't turn on anymore (a brief little movement from the fan) and PPBUS_G3H is 11.92V
Original charger pulses again.
 
2informaticos

2informaticos

Administrator
Staff member
Do you get stable PPBUS_G3H with fake charger?
If yes, check 3V3/5V_S5 if present.

"I swear it wasn't shorted before changing Q7902 ahah"
If you think about short to ground, is true; wasn't.
But I didn't talk about short to ground; Q7901 was shorted D-S!!!
 
2informaticos

2informaticos

Administrator
Staff member
You must check/change both Q7901/02 at same time.
If one of R7903, or D7900 is bad, then Q7901 will burn again; after that, Q7902 will burn easy too.
Be sure to have good solders and traces.
If Gate pin of Q7901 remains "on air", it will get burnt.
 
M

mikiotty

New member
I’ll check again tomorrow. I noticed that if I spray some alcohol on that zone of the PCB, the MagSafe light goes out and starts blinking… could this give you a hint on what’s happening?
 
M

mikiotty

New member
Believe it or not, that’s the absolute first thing I did even before writing on this forum. No difference.

R7903 is 2.8ohms vs the 2.2 it should be as per schematic (on my donor board it’s the same thing, 2.8 vs 2.2).
D7900 is .163 on one way in diode mode and 33Kohm in resistance mode the other way.
 
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M

mikiotty

New member
After resoldering U7900, I get a solid green light. No PPBUS_G3H and U7900 gets really hot (I cannot touch it with my finger, it will burn me).
 
2informaticos

2informaticos

Administrator
Staff member
Strange, no low values at all.
Be sure to have correct resistance between pins 19/20 and 21/22.
Check for short (between their pins) Q7901/02.
Also check D7903.
 
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