E5550 not turning on

[questore]

Dear All,

I have a Dell latitude e5550 (LA-A911P r1.0) that I bought as faulty. I would like to fix it.

Initial symptom was:
- Charger plugged in and the light on the charger stays on.
- When power button pressed, no reaction on laptop.
- After disassembly I have found a shorted capacitor so removed it.

Current symptoms:
- PQ4 has 20v on the source and gate but only 9v on the draing side.

What is your suggestions?

[mon2]

Re: E5550 not turning on

1) Are you using the official Dell power adapter for this laptop ? It is important to do so.

2) Dell adapters use a single wire communication protocol to extract out the details of the power adapter. If not found, the logic board will not power up.

This communication is over the PS_ID line. Meter in voltage mode.

What is the voltage to ground of this pin ?

3) PQ4 is a P-channel mosfet. This means that the GATE voltage must be LOWER than what is being passed between the SOURCE / DRAIN pins to ENABLE.

With gate voltage @ 20v, this mosfet is being instructed to remain OFF.

4) What is the voltage to ground of PL3 (with the adapter connected)?

This voltage will confirm if PD5 is shorted or not. Often this TVS ESD diode gets shorted from an ESD / over voltage event. A shorted diode will shunt the communication of the single-wire interface.

[questore]

Re: E5550 not turning on

Thanks for the advice.

As I have read your post I remembered that I have checked PQ4 and source to gate was 0 Ohm (adapter not plugged and plugged also 0 Ohm)
This meaning that PQ4 is faulty right?
BTW: Charger is official DELL

[mon2]

Re: E5550 not turning on

Be sure to NOT measure resistance or DIODE mode readings with power on. Each must be with power OFF.

Yes, if such a reading, then pq4 is defective. Apply flux, low air pressure and ample heat to remove this part.

When the part is off the logic board, allow it to cool down. Then measure the same pins of this part while it is on your desk. Likely it is damaged and should be replaced.

Do share the other requested measurements. As a quick test, can use a piece of wire to bypass the source and drain pins. Best to replace the mosfet so that it can continue to protect the ps_id line from over voltage spikes.

[questore]

Re: E5550 not turning on

Thanks. I try to get a replacement after confirming faulty PQ4

Be sure to NOT measure resistance or DIODE mode readings with power on. Each must be with power OFF.

Yes, if such a reading, then pq4 is defective. Apply flux, low air pressure and ample heat to remove this part.

When the part is off the logic board, allow it to cool down. Then measure the same pins of this part while it is on your desk. Likely it is damaged and should be replaced.

Do share the other requested measurements. As a quick test, can use a piece of wire to bypass the source and drain pins. Best to replace the mosfet so that it can continue to protect the ps_id line from over voltage spikes.

[Vesko356]

Re: E5550 not turning on

https://www.badcaps.net/forum/showthread.php?t=89452

[questore]

Re: E5550 not turning on

After Changing PQ4 the laptop tuns on fine. Thanks for the help. How can I change the thread name to SOLVED?