A-820-00840 - Stuck at 5V 0.05

[nameless]

Hey everybody I've got a motherboard A-820-00840 but it's kinda messy.

HISTORY :
The customer brought it saying that it suddenly won't turn on. He said that the laptop was always and only serviced by Apple Store. It appears that they already replaced the screen and the motherboard ))))

When I opened it I was shocked : several screws were missing and others were all over the board. One screw was stuck between pin 1 and 2 of the R7020 and C8036 was destroyed !! (pics attached)

MEASUREMENTS :
I pulled the board out and replaced R7020 and C8036 and was getting 20V and the apms were getting up to 0.70 and resetting to 0.05, basically looping.

I started to do some measurement around U7000 (C7078 and C7020) and suddenly (I might have short-circuited smth) i'm getting only 5V at 0.05A

Other measurement I did

PPBUS_G3H - 0v
PP5V_LDO5V - 0v
PP3V3_S5 - 0v
PP5V_S4 - 0v
PP1V2_S3 - 0v
SMC_RESET_L - 0v

PP3V3_UPC_XB_LDO - 3.3V
PP1V8_UPC_XB_LDO - 1.79V
PP1V1_UPC_XB_LDO_BMC - 0V
PP1V8_UPC_XB_LDOD - 1.79V

PP3V3_UPC_XA_LDO - 3.3V
PP1V8_UPC_XA_LDO - 1.79V
PP1V1_UPC_XA_LDO_BMC - 0V
PP1V8_UPC_XA_LDOD - 1.79V

C7078 - 5V
D6905 - pin1 - 0V, pin2 - 5V, pin3 - 5;V

Thank you for all your support

Best regards

 

[2informaticos]

Start checking diode mode to ground at PPBUS_G3H; be sure F7000 is good.
Post U7000 basic voltages; P_IN, AUX_DET, SMC_RST_IN. VDDA/P, EN_VR1; SMC_RST*, AUX_OK, A/BMON.

 

[nameless]

thank for your reply )

F7000 - is good
PPBUS_G3H - 0.45
U7000 :
P_IN - 5V
AUX_DET - 1.28V
SMC_RST_IN - 0V
VDDA/P - 0.38V
EN_VR1 - 0.29V
SMC_RST - 0.1V
AUX_OK - 0V
A/BMON - 0.28 on both

 

[2informaticos]

"VDDA/P - 0.38V"
Check diode mode to ground on both.
If good, change U7000.

 

[nameless]

Great I've got back the 20V after replacing U7000.

So now I have steady 20V, fan spins ones and amps go to 0.6 and back to 0.05A

So basically looping as before I short-circuited the U7000

 

[2informaticos]

Do you get stable PPBUS_G3H voltage?

Check if voltage appears on big coils each time fan spins.

 

[nameless]

it goes like this

when plugged, voltage goes to 3.6V
when fan starts to spin, goes up 13V
after back to 3.7V, then 4V, then 0V and back to 13V

and fan does spin any more.

Tested on F7000 pin2

 

[2informaticos]

I'm not sure what you've meant.
Can you check ALL big coils for voltage pulse (at least), when fan spins???

 

[nameless]

oh okok sorry for confused post

so fan spins only once then stops and doesn't spin anymore.

on coils I get

L7210, L7220 - pulsating 0.94V to 0V
L7370 - pulsating 1.05V to 0V
L8060, L7900 - pulsating 1V to 0V
L7960 - pulsating 0.9V to 0V
L8030 - pulsating 1.2V to 0V
L7030 - pulsating 13V to 0V
L7730 - pulsating 1.05V to 0.65V
L7410,20,30 - 0V
L7960 - pulsating 3.3V to 0V
L8410 - 0V
L7670 - pulsating 5.1V to 0V

 

[2informaticos]

Test to power on in SMC bypass mode.

 

[nameless]

still the same behaviour.

Tried on both ports : it goes till 0.60-0.65A and back to 0.05A and steady 20V

fan spins only once and rapidly stops

 

[2informaticos]

Probably bad CPU.
Power on sequence seems to completes, if you get VCORE pulse.
So there must be communication problem.

PLT_RST_L pulsing too?
Just in case, check for short and voltage pulse on all outputs from page 64.
Also check L7930.

 

[nameless]

yep also pulsating

PLT_RST_L - 1.29V
L7930 - 1.79V

on page 64 I have 4x mono speaker amplifier, is that it ?)

I'm using 820-00840 (ZEON) Schematic diagram

 

[2informaticos]

I have X502/MLB CATZ schematic.
Page 64 is about Power FETs, in my case.

 

[nameless]

sorry for late reply was very busy

hmm weird on first attempt to measure on U8200 I had basically the same OUT 1.79

but on further attempts i'm getting 0V on IN and OUT

U8200
U8205
U8210
U8220

VIN1 - 0V
VOUT - 0V

 

[2informaticos]

What voltages do you get on the board now?
Seems that no S5 at all...