Macbook A1706. 820-00923-A. Black Screen.HELP

[PITERPENY]

Hi all . I really need your help. A MacBook arrived with a broken display to replace the display. After replacing the display the image disappeared. Everything works through the external screen. replaced some components with new ones and to no avail (U8400.U8500. U8501)
here are some measurements
PPBUS_G3H=13.07v
F8400=13v
PPVIN_S0SW_LCDBKLT_F=13v
PPVIN_S0SW_LCDBKLT_R=13v
ISNS_LCDBKLT_P=13v
ISNS_LCDBKLT_N=13v
PP5V_S0=5.14v
PPVIN_S0SW_LCDBKLT=0.018v (should be 12.9v)
PP5V_S0_BKLT_A=5.14v
PP5V_S0_BKLT_D=5.14v
BKLT_SD=12.97v
LCDBKLT_FET_DRV_R=0v (should be 5v)
PPVIN_SW_LCDBKLT_SW=0.035V (should be 55V)
PPVOUT_S0_LCDBKLT=0.002V (should be 55V)
EDP_BKLT_EN=0v (should be 3.3v)

[mon2]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

Review the voltage to ground of SMC_LID.

[PITERPENY]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

Review the voltage to ground of SMC_LID.

SMC_LID=3.4v

[reformatt]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

Are you sure it's a known working display? Any sign of damage to the cable between the motherboard and display PCB? Very common on these machines to have some kind of damage from liquid and this can be at either end. Check EDP_INT_AUX_N resistance to ground as a sanity check.

Backlight won't be enabled unless there is communication to the display via the EDP data lines. So you need PP3V3_S0SW_LCD and PP5V_S0SW_LCD present for that to happen. Based on my experience with earlier models, these voltages may only appear momentarily on boot, and disabled if no display is detected. An extension cable to a known working display would be advantageous when working on this on the bench.

[PITERPENY]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

Are you sure it's a known working display? Any sign of damage to the cable between the motherboard and display PCB? Very common on these machines to have some kind of damage from liquid and this can be at either end. Check EDP_INT_AUX_N resistance to ground as a sanity check.

Backlight won't be enabled unless there is communication to the display via the EDP data lines. So you need PP3V3_S0SW_LCD and PP5V_S0SW_LCD present for that to happen. Based on my experience with earlier models, these voltages may only appear momentarily on boot, and disabled if no display is detected. An extension cable to a known working display would be advantageous when working on this on the bench.

Yes, I checked the display with another board, it works well, I have several of them. The motherboard simply does not see any displays; I threw in a few that were known to be good and tested. does not see that the display is connected, which is why it is not turned on. The connector measured all the voltages in it are normal and it is clean.
according to measurements
EDP_INT_AUX_N=0.307v (15.57 kilo-ohms)
EDP_INT_AUX_P=0.180V (15.80 kilo-ohm)
PP5V_S0SW_LCD=5v
PP3V3_S0SW_LCD =3.3V
what else can you check? please advise

[PITERPENY]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

I have a very low voltage on the line PPVIN_S0SW_LCDBKLT=0.009v instead of 12.9 help restore
replacing Q8400 did not help

[mon2]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

This means that R8402 is just floating and not being pulled to ground. When the backlight is enabled, R8402 will be pulled low (to ground) and a voltage divider will be created at the gate pin of the pass through mosfet.

That is, the backlight input voltage of ~12 volts will be lowered by the resistor based voltage divider built by R8402 & R8401. This lower gate voltage on Q8400 will cause this P-channel mosfet to enable.

On a P-channel mosfet, the GATE voltage must be LOWER than the voltage being passed between source and gate pins. If the gate voltage is the same, the mosfet will remain off - as in your case.

If R8402 is not being pulled low then do confirm that R8402 is not damaged. The backlight IC must also be enabled to perform this task.

PS: You should be getting some beauty sleep not hacking

[PITERPENY]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

This means that R8402 is just floating and not being pulled to ground. When the backlight is enabled, R8402 will be pulled low (to ground) and a voltage divider will be created at the gate pin of the pass through mosfet.

That is, the backlight input voltage of ~12 volts will be lowered by the resistor based voltage divider built by R8402 & R8401. This lower gate voltage on Q8400 will cause this P-channel mosfet to enable.

On a P-channel mosfet, the GATE voltage must be LOWER than the voltage being passed between source and gate pins. If the gate voltage is the same, the mosfet will remain off - as in your case.

If R8402 is not being pulled low then do confirm that R8402 is not damaged. The backlight IC must also be enabled to perform this task.

PS: You should be getting some beauty sleep not hacking

As always, thank you very much for the extensive explanation. but even with the display connected it remains unchanged

[PITERPENY]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

Well, let's go back to the original problem: there is no backlight and it behaves as if the display is not connected
what else can I check?
R8402 =63.4K good

[PITERPENY]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

I have a very low voltage on the line PPVIN_S0SW_LCDBKLT=0.009v instead of 12.9 help restore
replacing Q8400 did not help

this is with the display connected

[reformatt]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

EDP_BKLT_EN=0v

Comes from the PCH. Do you see an image on the screen if you shine a light? Need to establish whether this is a display detection issue, or a backlight enable problem from the lid sensors.

Check SMC_LID_LEFT and SMC_LID_RIGHT signals as these go to the SMC. See if they toggle if you place a magnet on each one. SMC_LID is a OR'ed output from each sensor, hence why you need to check each one.

[PITERPENY]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

EDP_BKLT_EN=0v

Comes from the PCH. Do you see an image on the screen if you shine a light? Need to establish whether this is a display detection issue, or a backlight enable problem from the lid sensors.

Check SMC_LID_LEFT and SMC_LID_RIGHT signals as these go to the SMC. See if they toggle if you place a magnet on each one. SMC_LID is a OR'ed output from each sensor, hence why you need to check each one.

SMC_LID_LEFT=3.4v
SMC_LID_RIGHT =3.4v
SMC_LID =3.4v
image is also missing. No matter how much I shined the light, there was no image or backlight

[PITERPENY]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

all indicators are normal except EDP_BKLT_EN=0v

[PITERPENY]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

please tell me are these readings normal or is the processor dead?
EDP_INT_AUX_N=0.307v
EDP_INT_AUX_P=0.180V
EDP_INT_AUX_N=15.5 kilo-ohm
EDP_INT_AUX_P=1.5 kilo-ohm

[PITERPENY]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

[reformatt]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

FlexBV has diode readings for this board as 0.21V for each. Checked on a working board and both read that value. Lid sensors seems to be fine as well.

Both go to the CPU. The couple of donor boards I have here have EDP_INT_AUX_N shorted to deck from liquid damage. EDP_INT_AUX_P is either shorted or reads 0.3V. Does appear to be damage to the CPU data lines.

[PITERPENY]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

What is a safe temperature for removing the CPU? Is it safe to use a board heater temperature of 120 C (248F) and a soldering gun temperature of 300 C (572F)?

[PITERPENY]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

FlexBV has diode readings for this board as 0.21V for each. Checked on a working board and both read that value. Lid sensors seems to be fine as well.

Both go to the CPU. The couple of donor boards I have here have EDP_INT_AUX_N shorted to deck from liquid damage. EDP_INT_AUX_P is either shorted or reads 0.3V. Does appear to be damage to the CPU data lines.

thanks bro 👑

[reformatt]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

Cannot say what works with getting these off as I don't have the right BGA rework station for it. Then you need to work out what temperature profiles are needed for each specific board model. Would take some trial and error. The other issue is where are you sourcing the replacement from apart from another board (or China). Is it worth the hassle?

[PITERPENY]

Re: Macbook A1706. 820-00923-A. Black Screen.HELP

Cannot say what works with getting these off as I don't have the right BGA rework station for it. Then you need to work out what temperature profiles are needed for each specific board model. Would take some trial and error. The other issue is where are you sourcing the replacement from apart from another board (or China). Is it worth the hassle?

as you remember, I can't solve the problem with the SSD in one of my posts. I have 2 boards at work, one of them doesn't see the SSD, but on this one everything worked until the display was replaced, and since we came to the conclusion that the CPU is dead, why not assemble one of the two. Does anyone have any thoughts on whether it will be easier to transfer the CPU or the SSD zone?