Dell Inspiron 6400 can't turn on

[fddizon]

Re: Dell Inspiron 6400 can't turn on

giant and steve,

if first fet tested good off board, then its much better to remove it and feed (4 v low 1 amp increasing gradually) after the fet. bypassing the fet will shorten your troubleshooting time.
note: be very careful in doing this technique in other sections. you might destroy other components that are good by mistakenly applying over voltage.

please post correct schematic
thanks

[gianttora]

Re: Dell Inspiron 6400 can't turn on

giant and steve,

if first fet tested good off board, then its much better to remove it and feed (4 v low 1 amp increasing gradually) after the fet. bypassing the fet will shorten your troubleshooting time.
note: be very careful in doing this technique in other sections. you might destroy other components that are good by mistakenly applying over voltage.

please post correct schematic
thanks

Yes i alredy tested it off board and the fet is still in good condition.

Here is the schematic


I refer to page 45.

May i know how to feed voltage after the fet ? Any reference of video which i can refer to?

[SteveHart]

Re: Dell Inspiron 6400 can't turn on

giant and steve,

if first fet tested good off board, then its much better to remove it and feed (4 v low 1 amp increasing gradually) after the fet. bypassing the fet will shorten your troubleshooting time.
note: be very careful in doing this technique in other sections. you might destroy other components that are good by mistakenly applying over voltage.

please post correct schematic
thanks

Good point Fddizon, thanks for your input. Yes it would be safer to do that. Surely enough when injecting voltage to the other rails it should not exceed the voltage the rails designed to be. Have done a couple or more unnecessary damage by that stupidity myself.

[SteveHart]

Re: Dell Inspiron 6400 can't turn on

Yes i alredy tested it off board and the fet is still in good condition.

Here is the schematic


I refer to page 45.

May i know how to feed voltage after the fet ? Any reference of video which i can refer to?

Assuming the FET is now off board , feed the voltage after the FET. In the schematic it is marked as DC_IN+. Apply the voltage to the drain (pads) of PQ6. Read fddizon post earlier

[Ramee]

Re: Dell Inspiron 6400 can't turn on

here

[gianttora]

Re: Dell Inspiron 6400 can't turn on

I'm not sure whether i feed the voltage in a right way. I put black probe to the screw hole for grounding and red probe at the PC140 since you suggest to feed the voltage after the FET (PQ6). I'm doing this while PQ6 is off the board.

When i fed the voltage, regulated power supply showing the was a short occured and FET (PQ42) became so hot. So is it PQ42 is the culprit?

One more thing is my friend told me, if I want to replace faulty FET i just need to follow the last number from the FET code number. If even number just replace with even number. If odd just replace with odd number. Is it true?

[SteveHart]

Re: Dell Inspiron 6400 can't turn on

As usual, check the mosfet out of the board. If it is short, it is the culprit. If it is tested ok, then you'll have to search other components the same way as you did before, only this time with the second mosfet out of the circuit.

For the mosfet replacement, it's not always true odd number is P channel and even number is N channel mosfet. It depends on the manufacturers numbering system. And even when it's the same channel type you should consider things like voltages, ampere, Rds on characteristic of the mosfet. Better to read the datasheets first.

[gianttora]

Re: Dell Inspiron 6400 can't turn on

As usual, check the mosfet out of the board. If it is short, it is the culprit. If it is tested ok, then you'll have to search other components the same way as you did before, only this time with the second mosfet out of the circuit.

For the mosfet replacement, it's not always true odd number is P channel and even number is N channel mosfet. It depends on the manufacturers numbering system. And even when it's the same channel type you should consider things like voltages, ampere, Rds on characteristic of the mosfet. Better to read the datasheets first.

OK. I already removed PQ42. I did a test and found this mosfet is OK. I fed voltage at PR132 with 4 volt. Voltage value is decreasing to 0.4v and ampere increase more than 2.00 A. So I lowered the Amp to 1. No component became hot this time.

[SteveHart]

Re: Dell Inspiron 6400 can't turn on

Search the entire board for components that become hot, not just the surrounding area of PQ42. The shorted component may be placed far from PQ42, but still connected to +PWR_SRC

[gianttora]

Re: Dell Inspiron 6400 can't turn on

I found northbridge chip become hot when i fed the voltage. So do i need to reflow or reball this chip?

[fddizon]

Re: Dell Inspiron 6400 can't turn on

check pq39 and pq40. also PC132.
check resistance dc_in+ vs grnd. if shorted, test all components on this rail

check pc140, pc125, pc141 and pc135
also c578