macbook pro 820-00840 have image no backlight

[kingskie]

Originally Posted by mon2

Refresh the list of voltage measurements

Voltage after fuse ?

Voltage before current sense resistor.

Voltage after current sense resistor.

Gate voltage of mosfet.

Voltage on drain of mosfet.

And so on..

voltage after fuse 13V
voltage before current sense resistor 5V
voltage after current sense resistor 5V
Q8401
pin 1-3 = 0.056V
pin 4 = 0V
pin 5 = 0.009V

[mon2]

voltage after fuse 13V
voltage before current sense resistor 5V

This is not correct. Please check again.
If still the same measurement then remove all power.

Check the resistance between the fuse and the current sense resistor.

It should be ~ 0 ohms.

There is something incorrect here. The voltage after the fuse must travel into and exit the current sense resistor.

Update..

What are the full markings of the chip you are replacing at u8400 ?

[kingskie]

Originally Posted by mon2

This is not correct. Please check again.
If still the same measurement then remove all power.

Check the resistance between the fuse and the current sense resistor.

It should be ~ 0 ohms.

There is something incorrect here. The voltage after the fuse must travel into and exit the current sense resistor.

Update..

What are the full markings of the chip you are replacing at u8400 ?

sorry my mistake. i measured wrong current sense resistor.

the current sense resistor is R8400 right?
the resistance between the fuse and the current sense resistor is 0.5 ohm
the voltage at the end of current sense resistor is 13V

hereby i attached the U8400 that i took from A1502

[mon2]

Is this a pic of the donor board or the board you are are repairing ?

[kingskie]

Originally Posted by mon2

Is this a pic of the donor board or the board you are are repairing ?

this is the pic of the board that i am working on. 820-0040

[kingskie]

U8400 i took from 820-4924-A

[mon2]

Use the boardview file to confirm that no parts are missing around this backlight IC:

https://www.badcaps.net/forum/showthread.php?t=69489

See some blank pads in the pic. Also no solder shorts.

Have not had enough quality time to review the same.

[kingskie]

Originally Posted by mon2

Use the boardview file to confirm that no parts are missing around this backlight IC:

https://www.badcaps.net/forum/showthread.php?t=69489

See some blank pads in the pic. Also no solder shorts.

Have not had enough quality time to review the same.

yes @mon2 all the parts are there. the bank pads is no stuff in the schematic.

[kingskie]

any suggestions?