Dell vostro 3510 backlight help

[nivirus2000]

Hi i got a dell vostro motherboard LA L241P with no backlight

LCD connector pin readings

1) 19.2V
4) 1.8V
5) 1.8V
7) 3.2V
29)3.2v
31) 3.2v
40) 3.2v

i followed the pin 1 line, the mosfet source and gate pin gives me erratic jumpy readings. please see attached.

any help will be appreciated
thanks

[mon2]

Re: Dell vostro 3510 backlight help

Hi. Unable to locate schematics for this one but see the silkscreen with 2021 datecode. Perhaps too current.

Remove all power.

Meter in resistance mode.

Check the resistance across each mosfet pair of pins as follows:

Source (1-2-3) & drain (5-6-7-8)
Source (1-2-3) & gate (4)
Gate (4) & drain (5-6-7-8)

Post each measurement and the meter scale used.

Pins 1-2-3 are joined together on the 8 pin mosfets. Respectively, 5-6-7-8 are grouped together as well. Confirm this detail before starting so that you have the proper orientation on the logic board.

Repeat for the next mosfet.

[nivirus2000]

Re: Dell vostro 3510 backlight help

measurements in diode mode with red probe to ground,

and yes you are correct the mosfets are grouped together
PQZ1 pin1-2-3 to PQZ2 pin 8
PQZ4 pin 1-2-3 to PQZ2 1-2-3

PQZ1
drain .470
source .059
gate .530

PQZ2
drain .059
source 0 grounded (normal)?
gate .456

PQZ4
drain .061
souce 0 grounded
gate .461

thanks in advance

[mon2]

Re: Dell vostro 3510 backlight help

Hi. Can you also measure the resistance across the pins on the mosfets?

Appears they may all be defective from your list with the low diode readings but let us see the resistance values.

See here:

http://electronicsbeliever.com/how-t...-is-defective/

[nivirus2000]

Re: Dell vostro 3510 backlight help

Resistance set under 20k

PQz1
S>D 5.80
S>G NULL
G>D 5.85

PQZ2
S>D .05
S>G 5.74
G>D 5.81

PQZ4
S>D .05
S>G 5.78
G>D NULL

PQZ3
S>D 5.84
S>G .95
G>D 7.12

Thanks

[mon2]

Re: Dell vostro 3510 backlight help

From the posted readings, each mosfet is defective. The resistance is too low for each.

Source fresh mosfets and buy spares.

Measure their resistance before you solder them on the logic board. Then test again with the fresh batch of mosfets. Lots of flux + heat + low air pressure and patience to remove and replace these parts.

[piernov]

Re: Dell vostro 3510 backlight help

Why mess with CPU VCore for a backlight issue? Sure way to kill the CPU.

[nivirus2000]

Re: Dell vostro 3510 backlight help

I haven't mess around those lines. The low resistance on the two inductors lines is becuse is a vcore line right? So that's normal?

[mon2]

Re: Dell vostro 3510 backlight help

Yes - my bad. The CPU is to the left side in your picture so these hefty mosfets are NOT for your backlight. Rather, they are the heavy current VCORE power rail mosfets. The VCORE rail will use multiple ganged up (but operate in phases) power supplies to support the pig of a current needed for the CPU.

The backlight is a very low current power supply. It is very possible that the backlight is defective INSIDE your panel.

Any chance you have another display panel you can use for testing ?

To confirm, you can see the display but it is only the backlight not working ?

See attached.

What voltage do you see on each of these pins with the LCD attached ? Measure with care with your meter.

[Udemzy]

Re: Dell vostro 3510 backlight help

Have you check lid_switch# ?

[rediii]

Re: Dell vostro 3510 backlight help

can someone please help me break the password 8fc8

please refer to the bios section and ask for help there... start a new thread