Laptop Model: DELL 14Z-5423
Board Number: 11289-1
Fault: In Battery Mode Laptop Not Working . AC Adaptor Working Fine
Open the drawing, find the battery identification signal BAT_IN#,
plug in the battery and measure 2.4V, which is obviously wrong and normal is
0V.
I replaced it with new one that showed the battery level and could
be used to turn on the laptop but still couldn't charge. I saw that the
charging chip used in this one was BQ24727. I happened to have a BQ24737 on
hand, so I tried to replace it, but the fault remained the same.
After restarting the laptop, I find that
sometimes it prompts that the power of the adapter is not detected correctly,
and sometimes it boots normally. I wonder if the adapter power detection
circuit PSID_EC is abnormal.
First analyze the drawing. The PSID_EC circuit is sent to the EC
through the interface through PQ3801 and then through PR3807. The normal
voltage should be 3.3V. After measuring PQ3801, it was found that the D-level
voltage is 2.2V, the G-level voltage is 1.5V, and the S-level voltage is 1.5V.
Circuit analysis shows that PQ3801 is
controlled by an NPN transistor PQ3802. After 3.3V is divided by resistor
PR3811 and resistor PR3802, a voltage lower than 0.7V is obtained, causing
PQ3802 to cut off, causing 5V_S5 to pull up the G level of PQ3801 through
PR3803. PQ3801 is turned on.
After measurement, the voltage of pin 1 of
PQ3802 is 0.3V, but the voltage of pin G of PQ3801 does not reach 5V. Find an
NPN transistor to replace it.
After the replacement, the PSID_EC voltage
returned to 3.3V. After entering the system, it was found that the battery
could be charged normally. There is a detail that needs to be paid attention to
when repairing this Laptop.
BATSW1 in the red circle in the picture above, this switch should
be turned to the ON position. If it is in the OFF position, some batteries
cannot be recognized, and some batteries can be recognized, but they will not
be charged.
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