Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

[GfilipeZ]

Hi,

This machine has no traces of liquid damage or corrosion and displays image normally on external monitors.
So far the measurements I've made, lead me to conclude that the source of the anomaly must be the dpmux U9800.
But I would like, if possible, to have your help and opinion.

J8500:
(4) BUF_EDP_PANEL_PWR_EN = 3,42V
(45) PP5V_S0SW_LCD = 5,13V
(44) PP3V3_S0SW_LCD = 3,29V
(43) PPVOUT_S0_LCDBKLT = 0V

DP_INT_HPD_R = 3,27V
R8505 have normal value.

U8900:
(77) EDP_BKLT_EN = 0V

U8510:
(2) EDP_PANEL_PWR_EN = 3,28V
(3) PANEL_FET_EN_DLY = 3,42V
(6) DFR_DISP_PWR_EN = 3,42V
(10) DFR_DISP_SMC_RST_L = 3,42V
(12) SMC_RESET_L = 3,42V


If I have to replace the IC U9800, it has to be from a Logic Board with the same number. Because this IC is programmed, right?


Best regards!

[mon2]

Re: Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

Check SMC_LID voltage on J4501.

Also:

SMC_LID_RIGHT

SMC_LID_LEFT_R

SMC_LID_LEFT

[GfilipeZ]

Re: Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

check smc_lid voltage on j4501.

Also:

smc_lid_right

smc_lid_left_r

smc_lid_left

smc_lid = 3,42v
smc_lid_right = 3,41v
smc_lid_left_r = 3,41v
smc_lid_left = 3,41v

[GfilipeZ]

Re: Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

More anomaly analysis ideas?

[mon2]

Re: Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

Remove all power. Meter in resistance mode.

What is the resistance to ground of EDP_BKLT_EN ?

Resistance to ground of PPVOUT_S0_LCDBKLT ?

With the adapter & LCD connected, what are the voltage readings of the following?

F8400, pin # 1
F8400, pin # 2

ISNS_LCDBKLT_P
ISNS_LCDBKLT_N

I2C_BKLT_SCL
I2C_BKLT_SDA

[GfilipeZ]

Re: Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

Remove all power. Meter in resistance mode.

What is the resistance to ground of EDP_BKLT_EN ?

Resistance to ground of PPVOUT_S0_LCDBKLT ?

With the adapter & LCD connected, what are the voltage readings of the following?

F8400, pin # 1
F8400, pin # 2

ISNS_LCDBKLT_P
ISNS_LCDBKLT_N

I2C_BKLT_SCL
I2C_BKLT_SDA

Thanks mon2,

EDP_BKLT_EN = 9,8Kohm
PPVOUT_S0_LCDBKLT = 1,8Kohm

F8400, pin # 1 = 12,62V
F8400, pin # 2 = 12,62V

ISNS_LCDBKLT_P = 12,62V
ISNS_LCDBKLT_N = 12,62V

I2C_BKLT_SCL = 4,89V
I2C_BKLT_SDA = 4,82V

[mon2]

Re: Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

PPVOUT_S0_LCDBKLT = 1,8Kohm

This resistance, in my opinion, sounds low.

Can you remove the LCD display and check the resistance to ground again of this rail (PPVOUT_S0_LCDBKLT) ?

If the resistance is still low WITHOUT the LCD display, then proceed to desolder one leg of the diode @ D8410. Then check the resistance again to ground of PPVOUT_S0_LCDBKLT.

This method should allow us to isolate the possible bad cap between D8410 and the LCD display.

Post your readings. Do not power up - just use resistance checks.

[GfilipeZ]

Re: Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

This resistance, in my opinion, sounds low.

Can you remove the LCD display and check the resistance to ground again of this rail (PPVOUT_S0_LCDBKLT) ?

If the resistance is still low WITHOUT the LCD display, then proceed to desolder one leg of the diode @ D8410. Then check the resistance again to ground of PPVOUT_S0_LCDBKLT.

This method should allow us to isolate the possible bad cap between D8410 and the LCD display.

Post your readings. Do not power up - just use resistance checks.

Hi,

PPVOUT_S0_LCDBKLT (no LCD) = 3,1Kohm

PPVOUT_S0_LCDBKLT (no LCD neither D8410) = 2,5Kohm

I injected voltage on the "cluster" (without LCD and D8410), to see if any capacitor warms up, but nothing happens.

After that, I checked again the resistance on PPVOUT_S0_LCDBKLT, and the value was 178Kohm.

So I found, every time I plug the display without power to the adapter, the resistance drops immediately to 1,8Kohm. And if I apply some voltage again, it goes up to 178Kohm.

My only conclusion is that the display may be damaged.

[GfilipeZ]

Re: Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

Hi,

PPVOUT_S0_LCDBKLT (no LCD) = 3,1Kohm

PPVOUT_S0_LCDBKLT (no LCD neither D8410) = 2,5Kohm

I injected voltage on the "cluster" (without LCD and D8410), to see if any capacitor warms up, but nothing happens.

After that, I checked again the resistance on PPVOUT_S0_LCDBKLT, and the value was 178Kohm.

So I found, every time I plug the display without power to the adapter, the resistance drops immediately to 1,8Kohm. And if I apply some voltage again, it goes up to 178Kohm.

My only conclusion is that the display may be damaged.

Hi,

Any idea?

[reformatt]

Re: Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

Any A1706/A1707/A1708 that come in with backlight issues are predominantly damaged flexes in the LCD. Try another known working LCD first.

MUX damage only usually occurs with liquid damage on the LCD connector since the backlight voltage is right next to a data pin that goes to the MUX. Of course on models without the MUX, it destroys the CPU in this case.