Apple macbook 820-3115 stops working without ram

[justin35]

Ok, so i got this board 820-3115 a total mess by other person...

Green light was flickering fast, you have to look closer to notice.
Ppbus_g3h was arround 3v obviously no fan spin, just a pulse.
Reseated u700 because i did not like the job
Ppbus_g3 went to arround 12v
U7200 also nothing (no 5v no 3.3 nothing)
I changed u7200 still nothing...
The smc was heated with some sh%**y flux but without removing the fixation glue around corners...
I gave it a shot and reheated myself
Ppbus_g3h went to 12.28v
At this point i went on google (bad smc or smc not talking to u7000)
At this point, u7200 started working but no pm_slp4_l
All_sys_pwrgd, also missing.
I found out pp1v5_s0 was missing. Check for short.. 10ohm, traced back the issue by pulling out u7770 and injecting 1.5v resulted in warming the cirrus chip u6201. Took it out, short was gone.
I replaced u6201 (cirrus 4206bcnz, with cirrus4206acnz as i don’t have any bcnz)...
They have same pinout...

Here i started injecting 1.5v on u7770 output because i don’t have a spare one, and the one original fron the board outputs 0.15v

I took out smc reset chip u5010
Ppbus_g3h still 12.28v...

I put back the smc reset chip u5010, and also removed the factory glue holding smc, clean all the residues, and reheated smc then shake it a few times.
Surprise!!!
Ppbus_g3h 12.56-12.59v and fan is spinning!
Put on speakers and ram stick, and it chimes!!!

I took out speakers and ram stick to continue troubleshooting the board and here i noticed the fan starts with a “bump” then is going to full speed. Then it stops and the green light is flickering again...
No pm_slp_s4_l
No pp1v05
No 3.3v on u7200
Whe fan is stopping ppbus_g3h drops to 12.4v then goes back to12.55-12.56v

If i put back ram stick it stays on.

Any suggestions? I will hook up the board to display and try to run efi

[justin35]

Re: Apple macbook 820-3115 stops working without ram

Update, i've put the board inside an a1278 chassis and i had no backlight, i could see the screen is activated.
I traced the problem and found f9700 blown. I replaced with a 0ohm resistor marked as fuse on other laptop board just to see if it works.
Now i have backlight, board boots to os.
I was able to run os test which it passes.
It remains to put back a proper fuse, or this one is ok?! And also to put back a new u7770.
Battery is charging, everything seems to be ok.
No more green light flash or fan stop without ram stick, extremly wierd!!
Boards shows apple logo after 20-25sec, is this normal? (Classic hdd with disk plates and 4gb)
And another 20-30sec to shutdown...

Another thing i really don't understand is why i get only 2.5v on l3895 pin 2 ppvin_sw_t29bst??
I never seen 12.5v on that rail, and i have a few i5, i7 boards in working contition...

Thanks!

[piernov]

Re: Apple macbook 820-3115 stops working without ram

Better put back a proper fuse for a good repair.
Apple logo after 20 seconds is a bit slow, try PRAM reset and maybe try another drive…
Thunderbolt power rail will only show up when a thunderbolt device is plugged in and request power.