A1707 2017 LCD Dark after Liquid

[Strolch]

Hello,
i have a MacBook Pro 15 "2017 820-00281 and everything works. But the display remains dark! I have corrosion on pin 43 and pin 1 of the LVDS connector and that's why I replaced the U9850 and the LVDS cable! But the display remains dark! I have the display tested on the other MacBook, the display is 100% intact. I also installed the OSX on the external monitor. I have just measured F8400. Fuse is ok!
A help would be great ;-)

[mon2]

Re: A1707 2017 LCD Dark after Liquid

Check the backlight voltage for the display.

Voltage reading?

Try pram reset as well.

[Strolch]

Re: A1707 2017 LCD Dark after Liquid

Hi, how can i check it? Ore where?

[mon2]

Re: A1707 2017 LCD Dark after Liquid

See attached.

Any yellow marked location = backlight voltage.

Just be very careful with the meter probes.

Meter in DC voltage setting (200 volts is good as the LCD backlight should be 25V or maybe higher if working correctly).

Red meter to any of the yellow highlighted points - they are all connected together on the circuit board so any point will do.

Black lead of the meter to any ground point = metal shield is ok.

Also, when the laptop is on, shine a flashlight along the front face of the display - can you see any of the usual boot logo graphics / login screen, etc. ?

[piernov]

Re: A1707 2017 LCD Dark after Liquid

As it has been said many times, no point in troubleshooting backlight if there is no image.
Hard to see image on these LCD so at the very least LCD power rail should be measured to see if LCD is detected and powered.

[Strolch]

Re: A1707 2017 LCD Dark after Liquid

@when the laptop is on, shine a flashlight along the front face of the display.
Hi, at the front is nothing to see! Thats why i replaced the U9850.
I just took measurements! I have 0 volts at the points! I have 11.7V on the fuse nearby.

[Strolch]

Re: A1707 2017 LCD Dark after Liquid

I Have 0 Volts at the C84.... +CC78 Points.

[mon2]

Re: A1707 2017 LCD Dark after Liquid

Can you check & post the cap location where you are measuring this voltage? Unable to locate C84.

[Strolch]

Re: A1707 2017 LCD Dark after Liquid

i measured all the points you said Like on the picture. I have 0 volts D8410 also 0 volts

[mon2]

Re: A1707 2017 LCD Dark after Liquid

Check the PP5V_S0SW_LCD on J8500.

Post the voltages for 1, 2 and 3 of the attached.

[Strolch]

Re: A1707 2017 LCD Dark after Liquid

Hi, i have at the U8500 Pin 1 and Pin 5 5Volts! And at R8515 3,7Volts!

[mon2]

Re: A1707 2017 LCD Dark after Liquid

Confirm the same voltages and the other backlight voltage is reaching J8500.

[mon2]

Re: A1707 2017 LCD Dark after Liquid

Measure & post the voltage on R9855. Need to confirm if the MUX (multiplexer) that shoots out the video over the eDP port onto J8500 is enabled or not.

See attached.

If the MUX is enabled with a logic '1' (HIGH) then there is a possibility that the MUX itself is defective and not passing through the signals onto the display panel.

This is assuming the display panel is a known good display and the relevant voltages are present. Then it is down the video signals that are sent over the eDP lines but this MUX is between the GPU and this LCD connector.

The MUX resides @ U9850 and appears that there is a low cost TI equivalent for this device.

P/N HD3SS212
* datasheet is attached

[Strolch]

Re: A1707 2017 LCD Dark after Liquid

yes the Pin 45 has 5Volts

[mon2]

Re: A1707 2017 LCD Dark after Liquid

Also share the voltage reading for the backlight @ D8410.

Can you see any backlight on your display ?

[Strolch]

Re: A1707 2017 LCD Dark after Liquid

at R9855 i have 3,3Volts on the Pin1 and pin 2

[Strolch]

Re: A1707 2017 LCD Dark after Liquid

at the first post I write that I replace the U9850

[mon2]

Re: A1707 2017 LCD Dark after Liquid

Very good on the U9850 replacement - we can rule this out. You are confident the replacement went well for the soldering ? 'Made it dance' with flux & hot air tool ?

Perhaps reflow it if the ENABLE is logic '1' = means the MUX is enabled.

Curious on the backlight voltage reading (PPVOUT_S0_LCDBKLT).

If PPVOUT_S0_LCDBKLT is not 25+ volts then this rail is not working.

Proceed to remove all power, meter in resistance mode (2k scale is ok).

Check the resistance to ground of PPVOUT_S0_LCDBKLT (red meter probe) & black meter probe to ground. Checking for a low resistance which can cause this rail to be pulled down OR even shut off due to an excessive load (current draw).

Post all readings.

[Strolch]

Re: A1707 2017 LCD Dark after Liquid

Yes he danced, Flux+hot air!. Where else should I measure the voltage?

[Strolch]

Re: A1707 2017 LCD Dark after Liquid

i have no backlight on the display nothing