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820-02020 No backlight 0,8v on BKLT_EN_R

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Bravo2001

Member
Can't I just transform the low signal (0.8v) u8100 is giving to 1.8v? How would that work? I have a lot of donor boards but don't now which part I can use...

Apart from the backlight, this logicboard works perfectly with external screen and dim internal screen...

ps. this MacBook came in as "dropped damage" It has a small dent at the bottom case but no visual damage on board. Can it be that the screen is not being recognized? IPD_LID_OPEN_1V8 is 1.8v, can I test anything else?
 
2informaticos

2informaticos

Administrator
Staff member
If you get image on it, internal LCD is recognized.

You can force the enable signal, but is not sufficient for the backlight to work.
Backlight adjust is controlled through I2C bus.

If you want to test, remove RP842 and bring 3V3_SW_LCD to BKLT_EN_R (CP842 pad 1).
 
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Bravo2001

Member
Tried but no luck! What I noticed is that

“RP851 starts with 5.1v as soon as image apears goes to 4.8v”

this is not 4.8v it stays 5.1v. but the scl line still starts with 5.1v and goes to 4.8v. So as I understand there is no good communication…

What can I look at more?!?
 
2informaticos

2informaticos

Administrator
Staff member
Communication on the I2C bus can be confirmed with o-scope.

If you have time to waste, inspect SCL/SDA lines on both sides of UD050.
Should catch traffic when using backlight adjust.
Then you can check for activity on SCL/SDA lines of the I2C bus to UP800.

I suspect broken traces, or solders somewhere...
 
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Bravo2001

Member
Could not see anything extraordinary on UD050...

Figured out something else! On the small lcd flexcable pin 24 is broken. On the connector on the logicboard I get a good diode measurement (0.507) but when I connect the small lcd flex cable I get a O/L on the other side... So the LCD doesn't get a connection!

Tried different Flex cables but when I use another one I don't get image. Is there a difference between the M1 small lcd flex cable and the once before the m1?

To bad I only have 1 M1 here, so can't check... Maybe I can try to repair the flex cable?!

Could this be the reason why BKLT_EN is low?
 
2informaticos

2informaticos

Administrator
Staff member
M1 video connector has different layout.
Don't expect for video cable to have the same traces routed as old models.
 
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Bravo2001

Member
Back at it again! Was on a holiday. Got my small LCD cable but still no luck. Now im thinking this was the problem all along... But while I was looking somewhere else I destroyed something!

Bravo2001 said:
Pin 17 (BKLT_EN_R) is 0.208 should be 0.374 and give 0,82v
Click to expand...

I noticed that RP842 pin 1 has a diode mode reading 0.019 and 0v which was 0.187 and 0.8v. But should have been 0.375.

When I remove RP842 I can see diode mode reading of pin 2 is 0.575 and pin 1 is 0.019! im really out of ideas now!
 
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Bravo2001

Member
By some miraculous reason it works now. Al this time I was testing it out of the casing only with a screen connected.

I removed RP842 and forgot the put it back. When I put The logic board back in the casing it worked?! Only some times de screen stays black until the login screen comes. then it flikkers 5 times and comes back on.

I'm guessing the backlight chip is getting its enable signal from somewhere else?! I measured on pin 2 voltage is 0.180v.
 
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