A1502 - 820-4924-A - light ok - Not turning on - CPU warm - L7320&7310 short

samstown

Member
Hi,

A1502, no liquid, stop working suddenly. Yesterday, I've plugged magesafe, light ok, charging ok but not turning on, CPU warm and at some point fan was spining but nothin on screen, even with external light to check backlight issue.. no chemie.

Today, I took board out, L7320&7310 are short to GND. That means CPU .. so game over ?

Thanks
Sam
 

2informaticos

Administrator
Staff member
Pure short, or just low resistance?
Should compare with good board.
Normal value is aprox 0.010-0.015 in diode mode, I think; depending by CPU type.
 

samstown

Member
oh, I have 0.13. Could be SMC ?

L7320 & L7310 = 1.86V
F7710 (2) PP_BUSG3H = 12.60
L5001 - PP3V42_G3H = 3.41
 

2informaticos

Administrator
Staff member
Fan will not spin untill CPU gets really hot; is normal behavior for this board.

As VCORE is present, check PLT_RESET_L if goes high.
If not, check U1950 voltage on pins 7 & 3.

Did you check USB activity, or Caps Lock reaction?
 

samstown

Member
ok, good to know for the fan.

No caps lock, no USB activity
PLT_RESET_L = 0.0V
U1950 Pin 3 = 0
U1950 Pin 7 = 0
C1950 1 = 3.42

After 4 min, fan start to spin.
 

samstown

Member
U1950 , no corrosion. Sorry, I proabaly measure pin 7 incorrectly before.

1 = 0
2 = 0.09
3 = 0
4 = GND
5,6,7,8 = 3.41V
 

2informaticos

Administrator
Staff member
Something is strange there; be sure to measure correctly.
You can't get pin 7 high, without ALL_SYS_PWRGD.
Also shouldn't get VCORE in this condition.

Use test points surrounding U1950, instead of its pins.
 

samstown

Member
thank you. not sure what's going on.

i've measure again, first time I had 0V on 3 & 7 and 3 min after I had 3.42V. Now it's stable, 3.42V on test point.

If I want to test it, I only need to connect screen connector and magsafe, right ? I did it.. still nothing.
 

2informaticos

Administrator
Staff member
Just use an USB tester; keep the board alone on the desk.

Check PLT_RESET_L, if you get 3V at pin 3/U1950.
 

2informaticos

Administrator
Staff member
PLT stands for PLaTform.

Check all SPI Bus Series Termination resistors and their traces.
Also test with known good BIOS.
 

2informaticos

Administrator
Staff member
I have never saw a shorted resistor...
Resistors get usually open, or higher value because of corrosion.
 

samstown

Member
thanks. I don't have another 820-4924-A to test BIOS. Can I take from other board ? Is there any compatibility to check.
I have a flash reader, I can unsolder the BIOS to make sure it reads correctly.

I've checked those resistors, they are ok.

R6110 ok 22 ohm SPI_CS0_R_L
R6111 ok 22 ohm SPI_CLK_R
R6112 ok 22 ohm SPI_MOSI_R
R6113 ok 22 ohm SPI_MISO_R
R6114 ok 22 ohm SPI_SMC_MISO
R6115 ok 22 ohm SPI_SMC_MOSI
R6116 ok 22 ohm SPI_SMC_CLK
R6117 ok 22 ohm SPI_SMC_CS_L
R6118 ok 22 ohm SPI_IO2_R
R6119 ok 22 ohm SPI_IO3_R
R6120 ok 22 ohm SPI_CSO_L
R6121 ok 22 ohm SPI_CLK
R6122 ok 22 ohm SPI_MOSI
R6123 ok 22 ohm SPI_MLB_IO0_MOSI
R6125 ok 0 ohm SPI_ALT_CS_L
R6126 ok 0 ohm SPI_MLB_CKL
R6127 ok 0 ohm SPI_ALT_IO0_MOSI
R6128 ok 0 ohm SPI_ALT_IO1_MISO
R6130 ok 22 ohm SPI_MLB_IO2_WP_L
R6131 ok 22 ohm SPI_MLB_IO3_HOLD_L
R6132 ok 0 ohm SPI_ALT_IO2_WP_L
R6133 ok 0 ohm SPI_ALT_IO3_HOLD_L
 

samstown

Member
Thank you. I've check all traces are ok, can't find the culprint.

what is J6100 connector for ? There's nothing connected to it.

So I should try the BIOS path then ?

Customer said he tried to power it on last week, didn't work... he tried the day after and it worked and there was a message to contact apple support (no more details) and the day after... didn't boot... and never boot again.
 

samstown

Member
You mean, it can NOT for this model A1502 ? I don't have Medusa. I should desolder the BIOS, write it with the code you sent and solder it back ?
 
Last edited:

2informaticos

Administrator
Staff member
Sorry, I just corrected my previous post.

Need to desolder U6100 in this case; if no Medusa available...
 
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