[SOLVED]820-4924 no backlight

Gannons3

New member
I have an 820-4924 with no backlight, computer does get an image backlight is just not present. im getting the 12.5v all the way up to Q7700 but not after. No short to ground after the transistor .901 in diode mode both r7702 and r7701 are reading correct resistance also I am getting 5v on pin 5 of u7700
 

Gannons3

New member
R7750 and r7751 are both good, also which resistors are the pull ups, sorry for being an idiot. computer was liquid damaged, but looks as though someone ultrasoniced it already
 

dukefawks

Administrator
Try a known good LCD assembly. The LCD talks to the backlight chip to enable Q7700. Assuming you checked SMC_LID.
 

Gannons3

New member
i did check smc lid, 3.4v but i did try to get continuity from the data lines to the lcd connector, and i have an open line and what looks to be destroyed traces, would that cause no backlight
 

dukefawks

Administrator
I2C lines on pins 3 and 4 of LCD connector need to be good for Q7700 to open, this is communication bus with backlight chip to LCD.
 

Gannons3

New member
I didnt have any insulated wire left, so i ordered some, just wondering if the caps are important in that line or if i can just run a wire from r7752/3 directly to pins 3-4 of the lcd connector
 

dukefawks

Administrator
If you mean C8358/59 they are not critical. Why not just fix the corroded via near the LCD connector by poking a strand of wire through it. That is the common failure point in these lines.
 

Gannons3

New member
oh i didnt realize you could do that. the whole pad where it goes through the board is pretty much gone, just a slight strand is left
 

Gannons3

New member
i got the wires ran, no short to ground on them both to the right pins and have continuity still no backlight, 12.8v still isnt getting through q7700 anything else i can check or is the screen toast?
 
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