MacBook pro 820-315 CPU Vcore, no shime no picture, no brain. Help Guys.

[nerkkka]

Hi. All the time I found answers in the google, but this time I can't find anything. I have macbook pro logic board 820-3115-b. The problem with this board is: Fan spin in full speed, no image no chime. Have troubleshooted all rails is pressend except no voltage on PPVCORE_S0_AXG_R. Have replaced U7400 three times plus mosfet at the same time, replased SMC. No idea what can be wrong with this board.

U7400

Pin 13; 1.42V
Pin 45; 5.04V
Pin 4; 0.05V
Pin 24; 3.3V
pin 12; CPUIMVP_AXG_PGOOD voltage 0.19V,
pin 13; CPUIMVP_AXG_PWM2 0.72V,
pin 24; CPUIMVP_PGOOD 3.3V.
Pin 47; 3.3V
Pins ;21;23;22; 1.05V,
Pin 39; 4.3V;
Pin 40; 4.45V;
Pin 38; 0.0V;
Pin 35; 2.05V;
Pin 36; 1.94V
Pin 8; 0.0V
Pin 6; 1.12V
Pin 10; 9; 0.0V
Pin 11; 5.04V
Pin 18; 15; 16 0.0V
Pin 14; 4.78V
Pin 31; 4.58V
Pin 33; 1.11V
Pin 32; 1.54V
Pin 34; 6.16V
Pin 44; 1.12V
Pin 3; 1.12V
Pin 43; 1.12V
Pin 41; 1.12V
Pin 42; 1.12V
Pin 28; 4.57V
Pin 26; 1.11V
Pin 27; 1.53V
Pin 25; 6.15V
Pin 48; 0.57V
Pin 1; 0.47V
Pins 19; 29; 5.09V
Pin 46; 5.04V

[piernov]

Re: MacBook pro 820-315 CPU Vcore, no shime no picture, no brain. Help Guys.

Try PRAM reset.
Check CPU_RESET_L.
Try to flash the BIOS. (save the old one) Or try with a BIOS chip from another board.

[nerkkka]

Re: MacBook pro 820-315 CPU Vcore, no shime no picture, no brain. Help Guys.

Hi. Thanks for a fast replay.
I have tried bios chip from another board, also tied reset SMC and PRAM. CPU_RESET_L is present 1.05V.
What else can be wrong with this board? If dead CPU then will put them to spares.

[piernov]

Re: MacBook pro 820-315 CPU Vcore, no shime no picture, no brain. Help Guys.

Yeah no way to know what's going on at this point. Not really worth putting more time into it.
History of the board? Liquid damage, drop, overheating…? Try to go over the whole board to spot any liquid/corrosion/knocked off component.
You could check activity on BIOS and communication between SMC and PCH on LPC bus. But it's often useless.

[nerkkka]

Re: MacBook pro 820-315 CPU Vcore, no shime no picture, no brain. Help Guys.

What you know about PPVCORE_S0_AXG? Because it is missed. Have checked on working board and there was around 0.5V. I have few boards with the same issue, that's way I would like to figure out and fix these boards.

[piernov]

Re: MacBook pro 820-315 CPU Vcore, no shime no picture, no brain. Help Guys.

PPVCORE_S0_AXG won't be present if the BIOS doesn't run or fail POST early.
Most likely missing without display connected too.

Also not beeping without RAM?

[nerkkka]

Re: MacBook pro 820-315 CPU Vcore, no shime no picture, no brain. Help Guys.

No any beep, just starts and runs. I don't have a lot of experience with CPU vcores. If all rails are working, then I thing dead CPU. What resistance should be on CPU vcore and on the AXG?

[piernov]

Re: MacBook pro 820-315 CPU Vcore, no shime no picture, no brain. Help Guys.

Dunno on AXG, but doesn't really matter here, apparently doesn't even start the POST procedure as there is no beep without RAM. On VCore the resistance may be between a couple of ohms and 10 ohms or so, depending on the CPU (and temperature, and if it's in a good mood). i7 may have a lower resistance than i5, not a general rule though. Sometimes a high end i7 will have a resistance lower than 2 ohms.

First culprit is still BIOS here. Then could be SMC, PCH, CPU, missing resistor… no way to know except replacing them or going all over the board to find something visually wrong.

With an oscilloscope you could probe 25Mhz PCH clock, SPI ROM CS# and SMC LPC bus LFRAME#.

[nerkkka]

Re: MacBook pro 820-315 CPU Vcore, no shime no picture, no brain. Help Guys.

Thanks for your big help. I will try what you have said, if can't fix this boards then I have more boards for spares

[nerkkka]

Re: MacBook pro 820-315 CPU Vcore, no shime no picture, no brain. Help Guys.

Hello everyone.

Who are good skills to fix macbook pro 13" 820-3115?
In last few weeks got few macbook with the same problem, they don't have brain.
Some one can explain going communication between PCH-CPU-SMC-BIOS.
I'm not good enough with CPU.
I hope so some master takes time to explain detailed how it's working.
Watched Louis on youtube, but hes just showing how to fixing and no detailed explanation.
If some one makes good post it will hell for a lot people.

Thank YOU