Dell XPS 13 9370 no power USB amp meter reads 5V , 0.11A

[waakye]

Hello fellow bad caps members,
I have a Dell XPS 13 9730 that a picked up today. The seller claimed that it stops working all of a sudden. The ammeter reads 5V, 0.11A.
Could some help me out.
Thanks.

[mon2]

Hey.

1) Powered by USB Type C so CC1 / CC2 pins are used to negotiate the power delivery contracts. Being Type C, there is a PD controller onboard that starts the power path. PD controller is @ U21.

Flip the power head cable by 180 degrees and test if the voltage and current consumption change.

2) Remove all power. Meter in DIODE mode. Red meter lead, yes RED to ground. Black meter lead to point to test.

Test :

MUX_C_CC1
MUX_C_CC2

Post each measurement of the DIODE mode measurements. Checking if the ESD diodes that are camped on these pins are damaged or not.

Do visually inspect the Type C connector / contacts which may also be coated with cat urine or similar and causing poor connectivity.

[waakye]

Thank you so much mon2. I will check the measurements and reply back.

[waakye]

Below are the measure in diode mode with the red lead to ground.
MUX_C_CC1 = 0.0V read at C175 at pin 1
MUX_C_CC2 = 0.0V read at C176 at pin 1

Visually inspected USB C connectors and they look clean.

One thing I forgot to mention is that the when I connect the USBC ammeter to JUSBC3 connector, the ammeter does not even power up.

Thanks again for your help.

[mon2]

The diode mode measurements imply that each signal line is shorted to ground. This could be due to the ESD devices on the same lines.

Locate if you have onboard the diodes @ D60 and also D63. If yes, remove one of them and then measure the lines again using the diode mode. Do you now see a non-zero volt measurement with the diode(s) removed? One ESD diode will be camped onto one CCx line. If a surge event caused the diode to be damaged then you will see such a measurement.

[waakye]

I removed D60 and setting reading 0v at Mux_C_CC1 and CC2.
Thanks

[waakye]

I removed D60 and still reading 0v at Mux_C_CC1 and CC2.
U21 defective?
Thanks

[waakye]

I change U21 and now the ammeter on each USBC ports reads 5.03V and 0.00A.
Any help guys.
Thanks again

[waakye]

[waakye]

Any help guys?

[waakye]

I am measuring 5V at the USB C pin connector. It should be 20V

[mon2]

The PD contract will only switch to 20V provided the PD controller (U21) is functioning properly.

Remove all power. Measure the resistance to ground of:

MUX_C_CC1
MUX_C_CC2

Each should not be a low resistance to ground unless there is a shorted component on these signal lines.

U21 was replaced? Soldering ok? Perhaps flux and reflow the part and nudge gently with tweezers to insure there are no solder shorts.

Consider removing C175 and C176 to see if the resistance changes. With the diode mode measurement of 0v, there is a short on the line(s).

Also confirm if you have the VBUS voltage on each side of LT5. With 0A current draw, there is no real load on this VBUS rail.

[waakye]

Thanks mon2 for replying and helping me fix this board.
Below are the measurements with resistance to ground:

MUX_C_CC1 reads OL at C175
MUX_C_CC2 reads OL at C176
I guess the range is too large for my multimeter


With the meter in diode mode without C175 and C176 removed:
MUX_C_CC1 reads .545V at C175
MUX_C_CC2 reads .554V at C176

Voltages at LT5 reads:
5V at both sides

Thank you so much for this.

[waakye]

Do I still have to reflow the U21?

[mon2]

For now, perhaps not. There are no shorts on the CCx lines yet the board is not consuming any current.

Confirm that the PD firmware flash rom @ UT6 is being powered. Measure the voltage to ground on pin # 8 = VCC3V3_TBT_LDO_C.

[waakye]

Thanks again for the reply mon2.
UT6 pin 8 to ground reads 3.32V

[mon2]

Confirm if you have each of the following power rails. One will be the same as what you have measured. TI is the same company that builds the CD321x series found on the macbooks so anticipating the same logic to troubleshoot will be applicable.

Each goes to a nearby cap so may be easier to probe the capacitor (with caution).

[waakye]

Hi mon2,
I took the following measurements from U19, 20 and U21.

U19
H2: at C141 reads 0V
G1: at C142 reads 3.32V
K1: at CT94 reads 1.780V
A2: at CT95 reads 1.785V
E1: at CT96 reads 0V

U20
H2: at C154 reads 0V
G1: at C155 reads 3.30V
K1: at CT97 reads 1.795V
A2: at CT98 reads 1.783V
E1: at CT99 reads 0V

U21
H2: at C167 reads 0V
G1: at C168 reads 3.32V
K1: at CT100 reads 1.786V
A2: at CT101 reads 1.783V
E1: at CT102 reads 0V

Thank you

[mon2]

Confirm if you have the voltage on +5VALW.

[waakye]

A11, C11, B11, D11 and H10 all reads 0V