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820-02020 No backlight 0,8v on BKLT_EN_R

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Bravo2001

Member
Hi,

Got a perfect logicbiard no traces of liquid only on pin 17 en 18 of UP800. Got chip off and saw that pin 18 was corroded bad. Cleaned it and replaced UP800 with one from 820-01598 (according to PDF, same model) Chip should get 5v.

Diode mode readings are ok except for pin 17 and 4

Pin 17 (BKLT_EN_R) is 0.208 should be 0.374 and give 0,82v
Pin 4 (LCDBKLT_FET_DRV) is 0.422 should be 0.550 (According to PLDaniels database).

What voltage should pin 17 be? And what can I do?
 
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2informaticos

2informaticos

Administrator
Staff member
As per schematic, VIH=1.2V; so it comes from 1.8V powered logic.
0.82V is prohibited value, can't be correctly recognized.
0 logic is between 0-0.4V and 1 logic is 1.2-1.8V...
 
B

Bravo2001

Member
Yes, sure tested with 2 different screens. Screens work on other board.

UB050 area very clean... Measured alle traces on UB050, diode mode readings all ok according to PLDaniels.
 
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Bravo2001

Member
RP850 starts with 5.1v as soon as image apears goes to 4.9v, diode mode 0.491
RP851 starts with 5.1v as soon as image apears goes to 4.8v, diode mode 0.491
RP852 5.1v, diode mode 0.276, also give 1.3kohm, according to schematics should be 1.8kohm
RP853 5.1v, diode mode 0.276, also give 1.3kohm, according to schematics should be 1.8kohm
 
2informaticos

2informaticos

Administrator
Staff member
Be sure DP800 is not shorted A-K.
Post diode mode to ground on both sides; w/ and w/o screen connected.
 
B

Bravo2001

Member
RP844 is also 10 ohm... Changed them with good 0 ohm donors from an 820-01598. Still same...
 
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Bravo2001

Member
Wauw, the fuse FP800 was blown... Gave 2.4v on pin 2. Changed that now getting 12v on source QP800, but gate is also 12v so no power to drain...


Bravo2001 said:
Pin 17 (BKLT_EN_R) is 0.208 should be 0.374 and give 0,82v
Click to expand...
Still think, it has something to do with the Enable signal? After all without EN the chip doesn't do anything... Why do you think EN is 0,8V? Is this enough to enable chip?
 
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2informaticos

2informaticos

Administrator
Staff member
0.8V is not sufficient.
I tought was clear before:
"0.82V is prohibited value, can't be correctly recognized.
0 logic is between 0-0.4V and 1 logic is 1.2-1.8V"

Apart of enable, UP800 requires correct communication through I2C_BKLT bus.
You should try to get UP800 from another M1 board.
This chip has firmware, not sure if is compatible the one you've used.
 
B

Bravo2001

Member
Ohh you mean the chip needs communication before it will get enable signal. But shouldn’t diode mode reading on EN pin 17 still be 0.374?
Im having a feeling the source of the enable signal is effected when up800 was shorted…

Is there a way to rule that out?
 
B

Bravo2001

Member
Hi, I read another forum that the backlight chips are interchangeable...

Seems like not an issue with UP800... But even when UP800 removed pin 17 stays @ 0.187 in diode mode! Should this not be 0.374?

A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-02016 - Badcaps

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Scherm­afbeelding 2023-02-09 om 14.55.08.png
 
2informaticos

2informaticos

Administrator
Staff member
"But even when UP800 removed pin 17 stays @ 0.187 in diode mode! Should this not be 0.374?"
You may have a problem with U8100 then; is connected on the same line.
No idea what should be the correct reading there.
 
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