Laptop Model: Dell 14-5420
Fault: The Laptop Does Not Turn On
After Connecting The Hard Disk.
Maintenance process:
The Laptop will not turn on even if the hard drive is inserted. The Laptop will turn on even if the hard drive is not inserted. Is the hard drive broken? Replaced the hard drive and still the same. Tested the power supply of the hard disk interface and found that the +5V_RUN voltage was abnormal and only 2.6VA
After checking the source, I
found that the power supply of the hard disk is converted from the standby 5V,
which is the secondary voltage. To pass the standby 5V, PQ16 must be
turned on, and PQ16 is controlled by PQ19.
In the standby state, pin 2
RUN_ON of PQ19 is low level, and then the above 5V conduction pulls it low to
cut off PQ16. When we press the power button, RUN_ON emits a 3.3V high level
conduction, causing PQ19A to cut off. The above +15V_ALW high level turns on
PQ16 to achieve secondary voltage conversion.
When I measured PQ16, I found
that the G level was only 5V. This must be abnormal. First of all, I ruled out
whether there was something wrong with the PR54 resistor. The measured
resistance value was normal.
When I measured pin 5 of PQ19A
again, it was 0V, which was normal. At this time, the PC44 was still the same
after being directly removed. Is there something wrong with the voltage of
+15V_ALW? But I don't think it 's possible because the voltage is
abnormal.
It was impossible to turn on
the Laptop with or without the hard drive installed, and the current would not
flow, that is, there was no secondary voltage. I mainly suspected that PQ16 had
lowered the voltage, so I removed it directly. I found that the G-level voltage
returned to 15V. After replacing PQ16 with a hard drive, the power came on. I
found that the fan was not spinning. I tested the 5V power supply of the fan
and found that it was not powered. I directly shorted pins 2 and 3 of U52 and
it was perfectly repaired.
Happy Repairing !!
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