Repair of Dell 14-5420 Laptop Connected with Hard Disk without Booting

Repair of Dell 14-5420 Laptop Connected with Hard Disk without Booting.

Machine model: Dell 14-5420

Fault phenomenon: the hard disk is not turned on.

Maintenance process: if you plug in the hard disk, you can start it without plugging in the hard disk. Is it because the hard disk is broken? Changed a hard disk, and it’s still the same. Test the power supply of hard disk interface, and find that the voltage of +5V_RUN is abnormal, only 2.6VA.

Maintenance of Dell 14-5420 Laptop Connected with Hard Disk without Booting Figure 1

Check the source and find that the hard disk power supply is converted from standby 5V, which is the secondary voltage. If the standby 5V wants to pass, PQ16 must be turned on, and PQ16 is controlled by PQ19.

Maintenance of Dell 14-5420 Laptop Connected with Hard Disk without Booting Figure 2

In the standby state, the two pins of PQ19 RUN_ON are at low level, and then PQ16 is turned off by the upper 5V conduction. When we press the power-on key, RUN_ON sends out a 3.3V high-level conduction to turn PQ19A off, and PQ16 is turned on by the upper +15V_ALW high-level to realize secondary voltage conversion.

When I measured PQ16, I found that the G level was only 5V, which was definitely abnormal. First, I ruled out whether there was something wrong with the resistance of PR54, and the measured resistance was normal.

When PQ19A 5 pin is tested again, it is also 0V. At this time, it is still the same to directly disassemble PC44. Is there a problem with the voltage of +15V_ALW? But I feel impossible, because this voltage is not normal.

It is impossible to start the machine with or without a hard disk, and the current will not run up, that is, there is no secondary voltage. It is mainly suspected that PQ16 has lowered the voltage, so it is directly removed, and it is found that the G-level voltage has recovered to 15V, and it can be turned on when the hard disk used for PQ16 is replaced. It was found that the fan did not turn, and the fan was not supplied with 5V power. The pin 2 and pin 3 of U52 were directly shorted, which was perfectly repaired.