820-01814 - 5V on charger 0.018A - Melted pins on the LCD connector

it-solve

Member
Another 1990 I am struggling with.
It has a slight liquid around U5440 / U6400 areas. Also what at the beginning looked like a little spill over the LCD connector bracket.

Lifted F700/1 to check on which side is the short seems like is on the board side.
U5440 - Disconnected R5400 to ensure U5440 is not shorting, short still persists

1.3Ohm Short on the PPBUS_G3H
No Short on the big coils

On close inspection I have noticed LCD connectors on the board melted.

IT-Solve_20-08-30_08-49-58.jpg
I don't get shorts on the melted pins on the connector

Even if I get the LCD connector replaced. This is a lost case right, looking at what lines shorted there?
 

2informaticos

Administrator
Staff member
LCD connector looks pretty ugly.
There is no schematic, nor boardview for this board.
You should eliminate first the short from PPBUS_G3H and change the connector after that.

Are you sure none of CPU coils have a similar 1 ohm value to ground?
 

it-solve

Member
I am using 820-01041 which is a pretty close layout

Resistance now is 2.72 Ohm on lifted PPBUS_G3H line of F7000/1

And same readings on PPVCC_CPU_PH1/2/3 coils

PPVCORE_S0_PH1/2/3 is even lower at 2.17Ohm

No Other coils have under 100Ohm readings

Thanks
 
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it-solve

Member
Okay lifted up L7211/21/31 coils and short 1.9Ohm remains on PPVCC_CPU_PH1/2/3 -> PPVCC_S0_CPU side.
PPBUS_G3H short is gone and shows 0.117 Vdc in diode mode.

What does this tell us? Besides a bunch of tiny filtering caps, these phase lines go straight to CPU. No liquid whatsoever in the CPU area. Can a melted LCD connector pins short a CPU?

Capture.JPG
 
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2informaticos

Administrator
Staff member
The low ohm value should be normal on PPVCC_S0_CPU.
At least one of U7210/20/30 is shorted; remove one by one.
 

it-solve

Member
Removed them one by one then lifted up all U7210/20/30's and L7211/21/31 coils. Short persists on PPVCC_CPU_PH1/2/3 lines.
 

2informaticos

Administrator
Staff member
I explained you that is no short at all; just compare with similar working board.
Resolder coils and remove mentioned chips one by one; when the short goes off from PPBUS_G3H, you've found the culprit...
 

it-solve

Member
I see what you mean. Found the doggy chip. Replaced it and no more short on PPBUS_G3H

I do get 20V/0.24A which then drops to steady 20V/0.08A with a bare board on the bench. No USB disk activity or HDMI output.

Where do I go now? All big coils a 0V apart than


PPBUS_G3H 12.585V
PPBUS_HS_CPU 12.585V
PPBUS_HS_GPU 12.585V
PPBUS_HS_OTH5V 12.585V
PPBUS_HS_3V3G3H_T 12.585V

PP3V3_G3H_T -
PP3V3_G3H_RTC_X - 3.356V
PP3V3_S0SW_TBT_X - 0V
 
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2informaticos

Administrator
Staff member
No pulse at all at 5V coil?
Be aware, CPU could resulted damaged, after overvoltage caused by shorted chip.
 

it-solve

Member
If you meant L3500, no pulse at all. In fact, there is no voltage at any secondary lines. No heat signature apart than USB-C chips.

I have PP5V_G3S 5.136V feeding U3500, nothing on the EN pin 15 though.

Where else I can look into?

Not even sure how U7220 burned on a first-place unless LCD connector has something to do with it. There is no residue on the board even around the LCD connector.
 

it-solve

Member
PP1V8_SLPS2R - 1.802V
PP1V8_AWAKE - 1.801V
PP1V2_AWAKE - 1.201V
PPVDDCPUSRAM_AWAKE - 0.801V

Shall I get remaining of the awake voltages?
 
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