Apple MacBook Pro A2485 - No backlight

[tommy97]

Hi everyone,

We're working on an A2485 MacBook with no backlight after liquid damage. The damage occurred near the backlight IC (UP800). We've checked all the nearby resistors and capacitors, and everything seems fine. We replaced UP800 from a donor board.

However, UP830 was also liquid damaged, and after cleaning, resistor RK830 came off. Unfortunately, I can't find its value, and the schematic doesn't indicate it as a critical component.

Would anyone have insights or a way to confirm the RK830 value?

Thanks in advance!

[mon2]

See attached. I see this as 10 ohms, 0201 resistor.

[tommy97]

I've replaced this resistor, still no backlight -

ppluxe_lx2 - 4.8v

LP800 - 0.250V
PPLIXE_LX2 - PPLIXE_LX1 0.250v
PPVOUT_LUXE_XW 0.250v

Checked everything around UP830 on diode mode everything in range of 0.200-0.800 but LUXE_ISL_R_P/N they're 0.0 as they lead to gnd i believe?

[mon2]

What is the voltage to ground of PP5V_S2_LUXE @ RP805 (pin 1)? This is the power rail to the backlight controller.

PP5V_S2_LUXE_VDDA ; should be ~5v

BL_PWR_EN ; is the backlight being enabled signal?

[tommy97]

PP5V_S2_LUXE_VDDA & PP5V_S2_LUXE 5.1v
BL_PWR_EN - Goes to 1.2v then drops to 0

(Both checked on new and old screen)

[mon2]

Good. So the logic board is attempting to turn on the backlight but then turns it off. This could be due to an excessive current draw of this display load and is being sensed by the circuit to power it down.

Remove all power. Measure the resistance between:

PP3V8_AWAKE_BKLTCONN_ISNS and PP3V8_AWAKE_BKLTCONN_ISNS_R

[tommy97]

I couldn't locate either of the section on the boardview, i checked by RD966 in between leg 1&2 - Short/OL 0.01Ohm.

isns_pp3v8_aon_blktconn_p TO isns_pp3v8_aon_blktconn_n - no connection in between

[mon2]

Apparently there are 2 versions of boards for the A2485 chassis.

There is:

820-02100
820-02382

Which one is yours? The 820-02382 does feature this current sensor for the backlight. Appears to be present in the schematic but in the boardview for the 820-02100.

Moving forward, with no power to the board, measure the resistance to ground of this backlight power rail. Do you have UP730 onboard? This is the LDO used to power the backlight.

[tommy97]

UP730 It is on the board. 820-02100-a

[mon2]

Measure the voltage of PPBCON_SW_REG from UP730 output pin # 1.

[tommy97]

PPBCON_SW_REG - 3.3v on RP732 / Pin 1 (It is called PPBCON_AWAKESW_BKLTCONN)

[tommy97]

Anyone?

[mon2]

Has the lid angle sensor been replaced?

[tommy97]

No, as i'm testing it on brand-new screen and i don't want to waste a new angle sensor. I did check section next to LCD Connector PPVOUT_LUXE_XW 0.078v, is there a way and possibility to trigger screen enable signal or is too risky?

[tommy97]

I've replaced lid angle sensor, there is no change. I've noticed that while JP600 connected laptop does not boot/no display externally.