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820-4924-A 2015 Retina 13in green light on charger no power on need some help

C

calbuh

New member
hi
I am new to apple board fixing sow please be gentle. I have fixed other type of motherboards but no apple mb until now.
I have this mb: green light on charger for few second after turn to orange (with no battery connected) and no fan spin ( i think this is normal at this model).
i have noticed a little area (like a drop of water) with corrosion on the following components :
r7742 ( 0 ohm had to replace) and
r7752, r7753 ( no component on motherboard only pad corroded)
there is no other area corroded , i have cleaned the board with ultrasound .... still nothing.
i have the following voltages and now i am stuck :

PPBUS_G3H 12.58V
PPBUS_S5_HS_COMPUTING 12.58
PPBUS_S5_HS_OTHER5V 12.58
PPBUS_S5_HS_OTHER3V3 12.58
PPBUS_S4_X239 0.00
PPVIN_S4_TPAD 0.00
PPDCIN_G3H_ISOL 15.17
PPDCIN_G3H 14.59
PP3V42_G3H 3.41
PPVRTC_G3H 3.34
PP5V_S5 5.024
PP3V3_S5 3.348
PP3V3_SUS 3.347
PP1V05_SUS 1.060
Smc_onoff_l 3.4 v


pm_slp_s4_l 0v
pm_slp_s5_l 0v


PP5V_S4 0v
PP3V3_S4 0v

U8000, U8050 area is like new

around u7501:
Pp5_s3_reg 5v
p3v3s5_drvh 3,3v
ppbus_s5_hs_ other3v3 12,5v
p5vp3v3_vreg 3,25v
s5_pwr_en 3,4v
sg_pwrgd 3,37v
p5vp3v3_skipsel 1,98v
p3v3s5_csp2 3,32v
p3v3s5_csn2 3,31v
p3v3s5_vfb2 1,8v
p3v3s5_comp2 1,95v
pp5v_s5 5v
p5vp3v3_vref2 1,98v
smc_pm_g2_en 3,4v
p5vs3_comp1 1,98v
p5vs3_vfb1 0v
p5vs3_csn1 0v
p5vs3_csp2 0v
p3v3s3_pgood 0v
p5vs3_en 0v
p3v3s5_rf 1,24v
pp5v_s3 0v
p5vs3_drvh 0v
p5vs3_ll 0v
p5vs3_vbst 4,78v
p5vs3_drvl 0v
p3v3s5_drvl 0v
p3v3s5_vbst 8,30v
p3v3s5_ll 3,31v
p3v3s5_drvh 3,32v
ppbus_s5_hs_other3v3 12,54v

on pin 3 (u7501) p3v3s5_rf is 1,24v ..... it is normal? not 3,3 v?

not sure this is relevant but SPIROM_USE_MLB 3.4v


i would appreciate any idea pls.... i am stuck
THX
 
C

calbuh

New member
no corrosion the area is like new ..
Charger is 60w and is the original one
pp3v3_sus is present on pin 8
Thx
 
D

dukefawks

Administrator
Measure carefully on PP5V_S4 and see if there is a pules(s) right after connecting power. If not check PPVRTC.
Best to check this with a scope as multimeters are slow especially auto range ones.
 
Last edited:
C

calbuh

New member
just when i connect the charger PP5V_S4 is jumping once an then stays down
PPVRTC_g3h is 3.32v constant
 
C

calbuh

New member
on PPVCC_S0_CPU i have noticed that i have only 10.6 ohm to ground and, on diode measurement i have 0.0006v, is this normal ? or the problem is around this ....
THX
 
J

jb23

New member
Does it run in SMC bypass mode? Hold down power button, plug in magsafe, wait 3 seconds, release power button, press power button again (should have a solid green light and fans will spin maximum)
 
C

calbuh

New member
pin 8 on u 1950 is clean and pp3v42_g3h is present,
in smc bypass mode:
I hold the power button connect the charger - amber light, release button - solid green , press button nothing happens.(green turns to amber)
i have noticed that also PPVCC_S0_CPU is jumping when i connect the charger.
 
D

dukefawks

Administrator
So CPU Vcore is pulsing. This usually means there is an issue with the SPI lines. Check all termination resistors and traces between them that go to U6100.
 
C

calbuh

New member
sorry my english is not so good. it is not pulsing only one jump when i connect the charger ... same thing whit other s0 and s3 voltages for example with p1v05s0_en, and the SPI lines are ok, clean and all the resistors have the correct values
 
C

calbuh

New member
i have check 2 times for a short on all voltage rails and i was unable to find any shorts
bu t i have noticed that
on pin 16 (u7501) there is 1.02v but before r7562 is 3.3v . on the schematic says 3.3v it is that ok ?
P5v_S5en is 3.4v ?
 
D

dukefawks

Administrator
PPBUS should be 12.6. I don't think you understand how R7562 circuit works.....

There is nothing I can do for this one but say termination resistors and traces in U6100 circuit, pin 8 on U1950. It could be 100 other things, inspect the board carefully. Pulsing power is THE worst issue to diagnose.
 
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