macbook pro 820-00840 have image no backlight

[kingskie]

Re: macbook pro 820-00840 have image no backlight

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]

Re: macbook pro 820-00840 have image no backlight

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]

Re: macbook pro 820-00840 have image no backlight

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]

Re: macbook pro 820-00840 have image no backlight

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

[kingskie]

Re: macbook pro 820-00840 have image no backlight

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]

Re: macbook pro 820-00840 have image no backlight

U8400 i took from 820-4924-A

[mon2]

Re: macbook pro 820-00840 have image no backlight

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]

Re: macbook pro 820-00840 have image no backlight

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]

Re: macbook pro 820-00840 have image no backlight

any suggestions?

[Sacred0489]

Re: macbook pro 820-00840 have image no backlight

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 ?

.

Hello, good afternoon, I have the same fault in 820-00850-A, I get 12 volts on both sides of the fuse, R8401 is fine, it has 80.6K and R8402 has 63.4K but my voltage is still 12 volts, I also don't have EDP_BKLT_EN, The resistance is correct any help i replace U8400 and Q8400 could you help me I'm starting in the world of macbooks

[mon2]

Re: macbook pro 820-00840 have image no backlight

Hello and welcome to the forum.

Does your macbook power up and offer a display? (without the backlight)

Can you see the usual graphics with the aid of a flashlight / cellphone torch light?

There is a lid sensor inside the trackpad. A hall effect switch is used to detect if the lid is open or closed.

You can check the voltage to ground of this lid sensor as a start. If the lid is considered to be open, then the ENABLE state will follow to enable the boost LED circuit @ U8400.

[Sacred0489]

Re: macbook pro 820-00840 have image no backlight

Hello and welcome to the forum.

Does your macbook power up and offer a display? (without the backlight)

Can you see the usual graphics with the aid of a flashlight / cellphone torch light?

There is a lid sensor inside the trackpad. A hall effect switch is used to detect if the lid is open or closed.

You can check the voltage to ground of this lid sensor as a start. If the lid is considered to be open, then the ENABLE state will follow to enable the boost LED circuit @ U8400.

Good morning and thanks for replay so fast.
yes the screen works without the backlight, we can see the dark image, regarding the lid sensor inside the trackpad it gives me 1.8 volts in IPD_LID_OPEN

[mon2]

Re: macbook pro 820-00840 have image no backlight

Remove all power. What is the resistance to ground of EDP_BKLT_EN?

[Sacred0489]

Re: macbook pro 820-00840 have image no backlight

Remove all power. What is the resistance to ground of EDP_BKLT_EN?

EDP_BKLT_EN 9kohms resistence to ground on R8442

[mon2]

Re: macbook pro 820-00840 have image no backlight

So it is not shorted.

Check the voltage to ground of:

ISNS_LCDBKLT_P
ISNS_LCDBKLT_N

There should be little or no voltage drop across these 2 test points else the boost circuit will be turned OFF due to an excessive current draw.

Confirm the resistance to ground of PPVOUT_S0_LCDBKLT. No power when checking resistance.

If the resistance is not low, continue...

Remove R8442. Solder a wire from R8442 pcb pad # 2 = EN pin on the backlight IC to a 3v3 rail on the logic board.

This is to manually enable the backlight IC with a logic '1'. This bypass should then provide for a voltage divider to lower the gate voltage @ Q8400 mosfet to allow for the 12V to enter the boost circuit.

Does this enable the backlight for your board?

[Sacred0489]

Re: macbook pro 820-00840 have image no backlight

So it is not shorted.

Check the voltage to ground of:

ISNS_LCDBKLT_P
ISNS_LCDBKLT_N

There should be little or no voltage drop across these 2 test points else the boost circuit will be turned OFF due to an excessive current draw.

Confirm the resistance to ground of PPVOUT_S0_LCDBKLT. No power when checking resistance.

If the resistance is not low, continue...

Remove R8442. Solder a wire from R8442 pcb pad # 2 = EN pin on the backlight IC to a 3v3 rail on the logic board.

This is to manually enable the backlight IC with a logic '1'. This bypass should then provide for a voltage divider to lower the gate voltage @ Q8400 mosfet to allow for the 12V to enter the boost circuit.
Does this enable the backlight for your board?

ISNS_LCDBKLT_P 11.96 Volt
ISNS_LCDBKLT_N 11.96 volts
PPVOUT_S0_LCDBKLT has no power and is not shorted to ground, on R8442 #2 = pin to BKLT_SD pin 1 is LCDBKLT_EN_L so the 3v3 i put on the pad #2 or #1

[mon2]

Re: macbook pro 820-00840 have image no backlight

See attached.

[Sacred0489]

Re: macbook pro 820-00840 have image no backlight

So it is not shorted.

Check the voltage to ground of:

ISNS_LCDBKLT_P
ISNS_LCDBKLT_N

There should be little or no voltage drop across these 2 test points else the boost circuit will be turned OFF due to an excessive current draw.

Confirm the resistance to ground of PPVOUT_S0_LCDBKLT. No power when checking resistance.

If the resistance is not low, continue...

Remove R8442. Solder a wire from R8442 pcb pad # 2 = EN pin on the backlight IC to a 3v3 rail on the logic board.

This is to manually enable the backlight IC with a logic '1'. This bypass should then provide for a voltage divider to lower the gate voltage @ Q8400 mosfet to allow for the 12V to enter the boost circuit.

Does this enable the backlight for your board?

ISNS_LCDBKLT_P 11.96 Volt
ISNS_LCDBKLT_N 11.96 volts
PPVOUT_S0_LCDBKLT does not present power and is not shorted to ground, I fed pin # 2 of the R8442 with 3v3 volt and I still do not have a backlight

[mon2]

Re: macbook pro 820-00840 have image no backlight

After you applied this bypass enable, what is the voltage to ground of PPVOUT_S0_LCDBKLT?

[Sacred0489]

Re: macbook pro 820-00840 have image no backlight

After you applied this bypass enable, what is the voltage to ground of PPVOUT_S0_LCDBKLT?

PPVOUT_S0_LCDBKLT i check the voltage in the bypass and is 3.3 volt but i still haved 0 volt on PPVOUT_S0_LCDBKLT