Lenovo Flex 5 14ARE05 LC55-14A U7204 help?

[ub6ib969]

Lenovo Flex 5 14ARE06 unit does not power on. When usb-c is attached U7204 (TPS66021YBGR-GP) gets very hot. I replaced it and still gets very hot. Unit is getting 20V and 0.228amps. when checking around I noticed that PC1051 & PC1052 are shorted (1V_VDDCR_SOC) does this mean that the APU1 is shorted ? or am i missing something? any help would be great.

[ub6ib969]

up

[mon2]

Remove all power. Meter in resistance mode. Measure the resistance to ground of the LDO and VBUS output rails. Post each measurement. If this component is heating up then there is an excessive current draw from the downstream side or one of the balls is shorted under this component of the replacement. Do review the soldering and consider to flux it well -> hot air the device

TPS6602x Integrated Source and Sink Power Multiplexer with VBUS LDO Regulator datasheet (Rev. B)

[ub6ib969]

thank you for you help mon2, below are the measurements:

black to ground and red to measure
VCCPD_VBUS - 1.755v
5V_SW_LDO (c7205) - .OL

red to ground and black to measure
VCCPD_VBUS - 0.524v
5V_SW_LDO (c7205) - 0.560v

i also noticed that PU4408 mosfet is receiving 20v however I am not getting anything at PU4407. This unit also have a dc jack.

[mon2]

Meter in DC volts (20 volts or higher is ok). Carefully measure the voltage to ground of the attached 6 points of interest. Red meter probe on point to test; black meter probe to ground.

[ub6ib969]

update

• when i remove PU4408 i get 19V_AD_JK =20V and PWR_ADOFF_G= 6.7V however once I replace back on board goes to 19V_AD_JK is 1.0V.
• with PU4408 on board and PU4407 remove 19V_AD_JK =20V and PWR_ADOFF_G return.
• if both mosfets on board 1.0V and I can see both mosfets pulsing.

[mon2]

Not what was asked in post #5 but let us continue.

Remove all power. Meter in resistance mode.

Measure the resistance across these same mosfets:

source (1-2-3) & drain (5-6-7-8)
source (1-2-3) & gate (4)
gate (4) & drain (5-6-7-8)

Check the above for PU4408 and PU4407.

Post each measurement. Checking for a low resistance to determine if the mosfet is leaky or not.

[ub6ib969]

here are the measurements, and thanks again.

PU4408
source (1-2-3) & drain (5-6-7-8) = 0.498V
source (1-2-3) & Gate 6 = .OL
gate 4 & drain (5-6-7-8) = .OL

PU4407
source (1-2-3) & drain (5-6-7-8) = 0.460V
source (1-2-3) & gate (4) = .OL
gate (4) & drain (5-6-7-8) = .OL

just a note when plugged in via dc jack PU4408 starts pulsing,

[mon2]

These are diode mode readings not resistance. On your meter you should have a resistance scale (omega symbol) and perhaps some scales. Post a front side pic of your meter to confirm. Proceed to use the resistance scales (not diode mode) for these checks. If you see 'OL' while in the resistance mode, then select a higher resistance scale.

A good mosfet that is not defective should have a high resistance reading.

[ub6ib969]

thank you for the lesson mon2 and below are the correct measurements
.
PU4408 2M measurement
source (1-2-3) & drain (5-6-7-8) = 0.695 M
source (1-2-3) & Gate 6 = 0.671m-0.673m
gate 4 & drain (5-6-7-8) = 0.560m

PU4407
source (1-2-3) & drain (5-6-7-8) = 0.480M
source (1-2-3) & gate (4) = 0.100M
gate (4) & drain (5-6-7-8) = 0.480M

[mon2]

PU4407 source / gate readings are low at 100kohms. Appears to be leaky.

Carefully, flux and remove this mosfet and then check the mosfet when it is on your workbench after it has cooled down.

[ub6ib969]

PU4407 20M - removed
source (1-2-3) & gate (4) = 0.L

[mon2]

Are these measurements on the mosfet while it is on your workbench? Check the same resistance mode measurements on the mosfet pcb pads. No power during resistance / diode mode checks.

[ub6ib969]

mosfet has been removed off the board and on bench.

diode mode
source (1-2-3) & drain (5-6-7-8) = 0.490v
source (1-2-3) & gate (4) = O.Lv
gate (4) & drain (5-6-7-8) = O.L.v

[mon2]

Can you post the model of your meter? The above table of values should be in ohms. Not clear if the meter is being used properly here.

[ub6ib969]

using victor vc890C
my bad measured in diode mode previously.

mosfet removed and tested using 20M resistance
source (1-2-3) & drain (5-6-7-8) = 1.12M
source (1-2-3) & gate (4) = 0.L
gate (4) & drain (5-6-7-8) = 0.L

[mon2]

These are good resistance measurements for source/drain.

Can you confirm the scale used for the other measurements? (source / gate; gate / drain)

[ub6ib969]

scale used was 20M ohm
source (1-2-3) & gate (4) = 0.Lm
gate (4) & drain (5-6-7-8) = 0.Lm

PWR_ADP_TOSYS found that c7203 is shorted after PR445. removed cap and still short.