[SOLVED]820-2936 start-stop loop three second intervals without any damage

Status
Not open for further replies.

Crizz

Member
So I got this A1278 820-2936-B machine in a absolutely perfect condition - no scratches, no dents, no liquid spill, no sights of usage at all :)

The Costumer told me it went off by itself and never come up again - battery is charged!

Now my results:
-green light is present and stays green (battery won't charge)
-the fan spins for a second then stops for 3 seconds and it starts again (loop)
-with battery only the fan spins for a msecond then it goes back to S5 state and stays there until I press the power button again
-all S5 rails are present
-all signals for S4, S3 and S0 come up in the time the fan spins
-SYSCLK works but I changed the chip anyway
-all S0 Rails come up in the time the fan spins - EXCEPT PPVCORE_S0

I don't know if it takes some time for PPVCORE to come up but I checked U7400 and I noticed TON pin is 12,6V and it drops almost to 0V in that moment the machine tries to go to S0.
R7402 stays at 12,6V on pin 2 so the voltage drop is related to U7400. I own a bunch of ISL and TPS chips but no MAXes damn, also no suitable donor board!

I ordered the replacement but in the meantime where I should look next? Have you any experience with this behavior?

image_197.jpg
 
Last edited:

aprendiz

Moderator
Measure resistance from R7402, if it is out of range, replace, my bet is resistor is bad...... and for no charge battery, check sense resistor R7050, R7051 and R7052 and traces....
 

larossmann

Administrator
Staff member
This is sounding like a sad SMC to me. I am hoping that you already checked R7402 and the traces, as well as checking current sense resistors by the U7000.
 

Crizz

Member
R7402 is bang on 90.9K and ALL resistors by U7000 are good :/
Changing the ISL was my next thought but it sounds arbitrarily...
What could cause the SMC to die?
Could the SMC cause the voltage drop at the TON pin?
 

dukefawks

Administrator
Voltage drop is totally normal, U7400 is fine also. My first action would be the BIOS, backup the old and try a good dump. If that works we can transfer over the ME region and serial #.
 

JorgePayar

Member
Voltage drop is totally normal, U7400 is fine also. My first action would be the BIOS, backup the old and try a good dump. If that works we can transfer over the ME region and serial #.
When I read this I have no idea what you´re talking about,and I think like me there are few of us.
A video about this would be awesome, or any post related to explaining it in several steps.
 

Crizz

Member
To be honest I didn't understand it at first time too but a quick google search revealed a bunch methods how to do it.
@DUKE: Also you mentioned these readers in another post here in the forum: EZP2010 and TL866

But I have so much stuff lying around here so I build a reader out of an arduino and now I´m testing it with a donor board.
However it is not 100% ready for action yet and the lag of information is immense.

The most threads out there want to achieve an iCloud remove and the most DIY leads also to this so it is kind of hard to collect the right informations.

larossmann
The demand for a DIY or example video is increasing
It would be great if we get one :)
 

Crizz

Member
You got to be kidding me .....
I got a Mac Air mid 2011 today with exactly the same behavior and the same readings and the same voltage drop on the MAX-Chip (witch I thing is normal) witch leads me to the point where I think I'm cursed since I get more of these nightmare jobs in the last days :((((

I will try the SPI ROM method when my reader is ready and hope the best.....
 

dukefawks

Administrator
Boot looping can be caused by anything. It just means the POST is not starting. Most of the cases will be corrosion somewhere, but a dead BIOS and 100 other things may also be the cause. So the symptoms are the same but the cause is probably different.
 

Crizz

Member
HURRRRAY machine works again :)

Solution was:
- read the SPI ROM
- extract my serial number
- download a clean dump and inject my serial number
- write back

.... and there was a nice LOOOOOONG DONG

looking back it was kind of though and troublesome since I had to start from scratch and had to collect all the information flying out there.
..maybe I should start making a DIY threat before I forget all the collected knowledge

Nevertheless Thank YOU all for your tips and especially Duke for your advice :)
 

JorgePayar

Member
HURRRRAY machine works again :)

Solution was:
- read the SPI ROM
- extract my serial number
- download a clean dump and inject my serial number
- write back

.... and there was a nice LOOOOOONG DONG

looking back it was kind of though and troublesome since I had to start from scratch and had to collect all the information flying out there.
..maybe I should start making a DIY threat before I forget all the collected knowledge

Nevertheless Thank YOU all for your tips and especially Duke for your advice :)
It would be so great Crizz I would enjoy so much if you do it. :) (diy threat)
 

Crizz

Member
Ok the Mac Air mid 2011 (post #8) works again too :)
Same Problem with the SPI ROM
Seems to be a common problem
 
Status
Not open for further replies.
Top