820-01521-A

Ictc

Member
How do I find out what is the missing signal or bad components that prevents the machin to power up ? I guess if U3900 could be the cause.

What other signals should I check for in order to narrow down the search to the required ones for booting at least?
 

2informaticos

Administrator
Staff member
Looks like missing CPU core power.
Could be CPU itself the culprit; or PCH, which is embedded in the same package.

Did you test with charger and battery, both connected?
 

Ictc

Member
No, I didn't connect the battery during tests. I'll do it but I need to know if the problem could arise in CPU area or somewhere else in the motherboard.
 

Ictc

Member
Sure I'll do it but need your suggeasions about what to test next. I arrived at the point that s0 state should already be reached and I wonder why still not powering up. What should I measure to get a clear picture of what is working and what is not? Cpu/pch? How do I know for sure?
 

2informaticos

Administrator
Staff member
ALL_SYS_PWRGD_R is enable signal for CPU core power.
Now PCH/CPU and BIOS/T2 control the specific power supply; enable signal is not sufficient.
 

Ictc

Member
Ok how do I know if the problem is with the BIOS/T2 or elsewhere? I tried restoring the T2 as I told you before resulting in just a padlock symbol and nothing else at the end of the process. I tought there could be something more straightforward to narrow down the issue.
 

2informaticos

Administrator
Staff member
This is not an exact science.
We don't have the tools used by manufacturer.
Bad CPU can be a reason for DFU not completed.
 

Ictc

Member
I agree but I tought you could have helped me at least in order to get to a diagnose without these tools, I'm not talking about solving the issue right now but at least know what sould be the fault responsable of the issue. If I should blame cpu/pch or BIOS/T2 chip. I do not know if the DFU was completed or not. I haven't found anywere an explanation of the symbol I get after the DFU... I can't say it didn't succeded because I have no experience on this new Apple tool that's why I'm asking the forum for help. I can't belive the only known problem with these machine could be just with the CD3215... It seems like when the infamous T2 chip gets involved engineers rise their hends up and stop thinking to other possible solutions ;-)
 

Ictc

Member
Resistance to ground measured on L7410, L7430, L7210, L7230 is respectively 14, 14, 20,5, 20,5
 

2informaticos

Administrator
Staff member
I don't have other board to compare.
But I don't see strange values.

Could be CPU, or T2 problem.
Each has lot of internal blocks and is sufficient one not working good.
 

Ictc

Member
Anybody capable to revive a machine like this in rossmangroup? :eek: Can't belive nobody went so deep in T2 problems solving yet. Hope someone can give me other suggestions in order to salvage this unhappy macbook.
 

2informaticos

Administrator
Staff member
If you like to waste more time on it, get a logic analyzer and monitor SPI bus and CPU SVID bus (R7102/04).
CPU works very hot on these machines, without heat pipe; so is the first suspect.
 
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