Works perfect if PM_SLP_SL4_L is pulled up, need advice :(

Hello everyone,

I have this old MacBook (A1278 K24 820-2530 board) which refuses to enter S3.

Actually, PM_SLP_SL3_L goes high, but PM_SLP_SL4_L remains low (this state is not described in the schematics).

After checking everything I could think of, I tried to solder a 470 Ohms resistor between PM_SLP_SL4_L and PM_SLP_SL3_L and ... it worked!

Everything turned on, I ran AHT (extended tests) and got no error.

I could leave it as is, but I don't want to for 2 reasons:

- putting the machine to sleep mode, or closing the lid, doesn't work, it even start boiling as the fan is off. One workaround would be to disable sleep mode, but it wouldn't make me happy.

- I'm too curious to give up ;)

For the record, I tried PRAM reset (no change), SMC reset (no change), SMC bypass (no sign of life, green light stays off).

I have the feeling that it's not a broken MCP79 solder ball, because everything works just fine with the pull-up resistor (and I don't want to go through a reball nightmare, I'm too unexperienced for that).

Can anyone please give me some advice, like telling me what signals I should check (I'm a bit confused with all the input signals MCP79 has)?

Thanks in advance for any help,


PS: it seems that when closing the lid, PM_SLP_S4_L is pulled up as expected, but because of my added resistor, S3 power rail keeps being powered, leading to a boiling motherboard because the fan is off.

As a workaround, I added a diode PM_SLP_S3_L |> PM_SLP_S4_L and it seems to solve the problem, but it's still a workaround.

So to summarize, MCP79 is not pulling up PM_SLP_S4_L during power-on phase only, and I have no clue why...

Répondez à cette question J'ai le même problème

Cette question est-elle utile ?

Score 0


Can someone explain to me under which circumstances MCP79 will pull up PM_SLP_S4_L???

I can't find a decent MCP79 datasheet :(


I would appreciate any hint, I'm kind of stuck


Reball the mcp? even if you wanted to do that how would that do anything? the mcp is wore out either chip or balls, order a pre balled mcp and lay it down, that model mbp mcp gives all kinds of problems as it ages.


thank you for the advice, I definitelly need to learn how to do a decent reball. Only made 3 attempts with an IR station and fried the chipsets each time...


Reballing is a waste of time! Find new chipset with solder balls, like I said the chip is worn out if your going to get into bga reworking you can set Brand new chip! Buy Jovy IR station or Honton. The only chip you should ever want to reball is the SMC only.


Afficher 1 commentaire en plus

Ajouter un commentaire