MacBook A1278 can't power on

[orientalsniper]

Hello all, been with this MacBook for a few months already, the issue lies on R5087: SMC_BC_ACOK (0.9V, should be 3.4V) - PP3V42_G3H (3.4V, this is good).

What I do is I replace the R5087 resistor (470k), use it for 30 minutes, then the magsafe light goes off and in a few minutes it will shutdown.

I've replaced U6900, U6901 and U7000 (charger IC) multiple times. R6929 is fine (2k ohms).

The problem lies on the SMC_BC_ACOK line. I really need help on this one.

[dellxps15]

Re: MacBook A1278 can't power on

did u try another magsafe and another power supply?

[orientalsniper]

Re: MacBook A1278 can't power on

Yes, sadly I've tried another power adapter and it happens the same (power going out in 20-30 mins).

[dellxps15]

Re: MacBook A1278 can't power on

did u try reset smc ?

maybe you are looking on the bad section. pc power off both battery only and dc only ?

if it power off only with dc, then check u7000 pin voltage.

[orientalsniper]

Re: MacBook A1278 can't power on

SMC Reset already done, power goes off even with battery plugged.

Macbook can only power-on if the pullup resistor (R5087) has 3.4V in both sides. When the SMC_BC_ACOK side of that resistor (R5087) has 0.9V, MacBook fails to power-on.

Now, SMC_BC_ACOK is CHGR_ACOK.

And CHGR_ACOK comes from PIN14 of U7000 (charger IC), I suspect something is affecting this IC, since PIN14 is also 0.9V, but how??? I've already changed twice this IC.

[dellxps15]

Re: MacBook A1278 can't power on

dont really know well how u7000 works. it has many voltage like 5volt, 3.4 volt, 16volt, 12.5 volt. on macforum some dude should be able to help you. but if pin14 of u7000 is low, something with u7000 should be bad.

or maybe something is bad with macbook pgood and smc send signal to shut down pc.

ps: when pc shut down, magsafe light is green ?

edit: on macforum searching google for "u7000 pin14 low" a good dude say that it could be a possible bad joint of that qfn. try to squize the solder iron on that side with a good flux and see if it goes ok.

look: http://forums.macrumors.com/showpost...postcount=1848

and specially look http://forums.macrumors.com/showpost...postcount=1867

[orientalsniper]

Re: MacBook A1278 can't power on

That's interesting, I'm sure U7000 is fine since I've changed it twice and I've checked the solder points with magnifying lens.

What I'm going to check are those resistors mentioned.

Thanks for the assistance.

EDIT: Yeah, magsafe light goes off before it shutdown (like 5-10 mins before).

[ictc]

Re: MacBook A1278 can't power on

dont really know well how u7000 works. it has many voltage like 5volt, 3.4 volt, 16volt, 12.5 volt. on macforum some dude should be able to help you. but if pin14 of u7000 is low, something with u7000 should be bad.

or maybe something is bad with macbook pgood and smc send signal to shut down pc.

ps: when pc shut down, magsafe light is green ?

edit: on macforum searching google for "u7000 pin14 low" a good dude say that it could be a possible bad joint of that qfn. try to squize the solder iron on that side with a good flux and see if it goes ok.

look: http://forums.macrumors.com/showpost...postcount=1848

and specially look http://forums.macrumors.com/showpost...postcount=1867

I had an identical issue coused by the bad solder joint on pad 14 of the qfn Q7000. Apparently the solder need to stick not just to the bottom side pads of the chip to make a proper contact...