3 Backlight connector shorted to ground - MacBook Pro 01708 2017
Hello everyone ,
I'm facing a backlight issue due to liquid damage on a macbook and I'm wondering if someone can help me .
My board is a A1708 820-0080-A
I already have few information after few measurement .
I'm not an expert on this but have few electronical notion .So I'm sorry if I cannot understand all specifical technical terms of your answers .
First below few things to confirm my issue :
- I have image but no backlight
- I can use the laptop but with an external screen
- When I opened the macbook the fuse was cutted
- few corroded area but not dramatical .
- I've cleaned everything to remove all those corroded area with a very soft brush and iso alcohol
- I think the caps are good after measurement with a multimeter . I found almost the sum of the capaticance value on the schematic . (probably not the right way but )
- In continuity mode with LCD connected (J8500) , the output line PPVOUT_SO_LCDBKLT is shorted to ground .It's the same when the backlight connector J0803 is disconnected .
* And last there is no shorting when the LCD is disconnected (J8500) .
- When I tried to measure for shorting on the J0803 connector (backlight) which is on the additional PCB attached to the screen with LCD completely disconnected to the main board , I found shortage between PPVOUT_SO_LCDBKLT and ground on the this connector which was also corroded . I guess this is the issue .
- Doest someone know if I can buy this connector somewhere ? or the name of this connector ? Is that an FPC type ?
*
- I've solder back a new fuse and measured 0.002v in the output line PPVOUT_SO_LCDBKLT.
- I also measured voltage on the first mosfet with is the Q8400 and the gate voltage which is 12v so it isn't the one expected around 5.2v as on the attached picture .
*
My understanding is the following : the backlight IC doesn't short the R8402 to GND so the voltage divider is'nt working properly . Why I don't know . Bad driver or due to the shorted output the driver doesn't allow the SD line to be grounded .
I hope someone can help me .
Thanks in advance for you time and help .
Mise à jour (04/12/23)
UPDATE 12/04/2023 : I removed the J0803 connector and still have the shorting . Which means that there is another circuit linked to the backlight on the T-CON board .
@littlegreenrock You were right something in going on where you pointed .
@flannelist you were also right , something is going on below the shield . But not easy to remove ..... I'll try anyway even if just for curiosity .
Right now I got a broken screen but good T-CON board .. I don't know if I'll be able to switch some components in order to repair the good one .
It's unfortunate because I know the LCD pannel is good and the backlight is also good .....
I'll probably have to change the whole screen .... :'(
I'll let you all know when I have some news
Mise à jour (04/18/23)
Update 18-05-2023
Hi everyone ,
I tested a working screen at least the backlight on my macbook and still no backlight . No short measured on the backlight output when the screen is connected via LVDS compared to before . So first good news .
Still no working backlight although which means that i have an issue on the MB .
I replaced the U8400 but no change . I still have the gate voltage issue which is not grounded so the same as the source (13v on pin 3 & 4) .
There is a lot of test point around this IC . And I want to test them in diode mode .
Does someone here have the value that I should get on those points please ?
Thanks for your help .
Mise à jour (04/23/23)
Hi everyone, little update.
I forced the R8402 pin 2 to be grounded and I get 12v at en backlight circuit output . Now I have 5.7v on the gate as it supposed to be . But no 44v for the moment .
Which means I have probably issue with the second Mosfet which boost the voltage . Does anybody knows how this second one works?
Ont question aswell , what's the meaning of those two signals ?
-TCON_BKLT_PWM
-EDP_BKLT_PWM
I read that if PWM signals is 0 . The backlight circuit will remains off . Some of the repair shop force that PWM signals to be a 3.3v which correpspond to 100% . If that's the solution I will go for it but in your opinion where to I have to inject the 3.3v ?
Thanks in advance.
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https://imgur.com/a/Xh9fObz
Your short is likely to be here somewhere.
- de Jade
Can you upload some pictures of what you’re looking at (you can edit your original post and add them in? Have you removed the shield over the components on the board?
- de Alisha C
@littlegreenrock Do you think it's possible that it's the connector itself . I was badly corroded before I cleaned it (only in the surface )
- de Riana
@flannelist what do you mean by what I'm looking at ? The J0803 connector picture on the post is mine .
No I didn't remove the shield for the moment . Do you know if it's glued or cliped ?
- de Riana
I meant a wider picture, just the connector itself is unlikely to be the issue, it’s just a convenient place to take measurements. I would want to see the backlight areas on the main logic board as well as the components under the shield on the TCON board (the board attached to the display).
The shield is soldered on, and it’s not always cooperative in the removal process, I usually resort to low melt solder for removal. Especially since there are cables attached to the display. Cables that melt. If there was liquid damage, and the actual logic board seems okay, the issue is almost certainly under that metal shield.
I will make a mental note to dig up the display I have at home that was in a similar machine (same model, just with the touchbar, so same model of display). It was probably significantly more damaged than your device, but there is a backlight chip on the TCON board as well, it’s possible that’s your issue. The one on mine literally had a hole burned in it from the short to ground.
- de Alisha C
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