Help 820-3437-B NO power on

[brumbrum]

I have a 820-3437-B macbook Air, and I need your help cause it's a really weird case.

At the benginning, it was dead, so here what I did:
- Replaced SMC from an identical donar board
- Removed one dead Ram chip that become really hot and was shorted, so now there are only 6gb on board and nomore 8gb

I thought it was ok after these fix, but now the behaviour is really strange:

With dc magsafe plugged only on board disassembled from macbook:

• All voltages look good, I get even VCORE, about 1.7volt
• I get 1 second green light, after stuck on orange light, fan start and stop spinning (like an smc reset), and after that speeds until max full ramp
• If I plug an usb mouse is powered only 1 sec meanwhile fan starts after stop

With board assembled on macbook:

• Battery is charging
• If I plug an usb mouse is powered only 1 sec meanwhile fan starts after stop
• no charm, no video, no backlight, nothing
• I get 1 second green light, after stuck on orange light, but fan is stuck slow spinning, like a good boot, and cpu is hot, but nothing happens
• If I press power button on Mac with magsafe connected I can reboot it, it's responsive; with only battery charged and no magsafe, if I press power button no response

Can you give me any advice or explain me what is happening? I'd really appreciate it, thank you

[piernov]

Re: Help 820-3437-B NO power on

Board won't POST without all RAM chips. Should probably cause 3 beeps but not sure.

[brumbrum]

Re: Help 820-3437-B NO power on

Are you 100% sure? Avtually I don't have any beep.
So should I replace all 4 ram chips?

[zpi]

Re: Help 820-3437-B NO power on

You can put identical one back. Board will not post woth three ram chips 100%

[brumbrum]

Re: Help 820-3437-B NO power on

I soldered a new one, now full ram, but same identical behaviour

[zpi]

Re: Help 820-3437-B NO power on

Is ram identical? It cannot be from diffrent manufacturer

[brumbrum]

Re: Help 820-3437-B NO power on

yes, from the same donar board of smc, same part number and same brand

[zpi]

Re: Help 820-3437-B NO power on

I guess smc is also from same part number logic board? Also did you tryed smc bypass mode?

[brumbrum]

Re: Help 820-3437-B NO power on

Yes of course, from a same number model board that I bought appositely.
Thanks for the tip, But if I keep pressing power button and connect magsafe (with or without battery it's the same) I got only orange light and fan is not spinning. When I release the power button, Green light for 1 second and after orange, but fan is spinning and same behaviour like described in first post

[brumbrum]

Re: Help 820-3437-B NO power on

I changed also bios from donar board.. but still nothing

[zpi]

Re: Help 820-3437-B NO power on

Does board make two bootloops as it should? Also check all spi rom termination resistors and vias

[brumbrum]

Re: Help 820-3437-B NO power on

could I get S0 and Vcore if any spi were missing?

[zpi]

Re: Help 820-3437-B NO power on

Yes, CPU is reading EFI, and to do that it needs vcore.

[piernov]

Re: Help 820-3437-B NO power on

Most of the time these boards will power cycle before VCore can even turn on if there's an issue around SPI ROM, because the PCH cannot read the soft straps.

[brumbrum]

Re: Help 820-3437-B NO power on

All SPI are good. I'm starting to think that the problem is the cpu/gpu