macbook 820-2849-A problem no video black screen no backlight

Laimis

New member
Hi everyone, working on this 820-2849 board. Its been driving me mad for the long time and i cant figure it out so decided to ask you guys some help. its been a pain and i know that it might be a dead video but i believe i can still fix it. Right so the problem is that macbooks starts as it should, chimes ok, but theres no backlight or video.i have checked all power rails and all power rails are pretty much ok. GPU vcore and cpuvcore both present. i have noticed that PPVCORE_S0_CPU starts with 1.05v with fans spinning but after fans starts to spin faster voltage drops to 0.89v . is it normal or needs to be investigated? Also came accross that GFXIMVP_ISNS_IOUT=SMC_GFX_ISENSE only 0.01V. anyway any suggestions where to start? ppbus_S0_LCDBKLT_FUSED power stops at Q9806 pin4. 0V pin 1.2.5.6. LCD_BKLT_EN -0V.
L9000 - 0V both sides. LCD_PWR_EN 0.01V .Changed u9000 no change. really desperate for some help or where to start.
 

Laimis

New member
Has anyone came across 820-2849 board with the same no video problem where the board turns on and chimes? LCD_BKLT_EN and LCD_PWR_EN missing
 

dukefawks

Administrator
First thing to check would be with an external monitor. To be sure connect a HDD that will boot fully into OSX so an external monitor can be recognized.
 

Laimis

New member
Hi Dukefawks. Good to hear from you. Yeah checked it already no signal whatsoever . HDD spins, chimes, but no image on external screen.
 

Laimis

New member
L8920 pin2 =0.91V, pin1=0.84V, seems to be ok. it has traces of liquid damage but all components and chips looks ok under the magnifier no obvious burns or damage. the thing is that i have came across 3 faulty 820-2849 laptops in some time and all 3 had the same symptoms. So i was really wondering whats the problem with these boards and why they end up like this .
 

dukefawks

Administrator
These boards are not known for such failures. Does the board actually boot form a HDD? Need to know if it even gets into OSX. Where was the liquid damage?
 

Laimis

New member
i doubt it boots to osx. cd-rom works usb works hard drive spins but keyboard caps lock not coming on when pressed. also cant do pram reset. if lid shut fans still spin as if its in some kind of sleep state. No obvious corrosions but some contacts oxidised . where shall i start? any ideas?
 

dukefawks

Administrator
If you cannot do a PRAM reset there may be more to this. It could be an EFI lock and it won't boot from any device besides the one it was locked to.
Was there any corrosion in the LCD connector area? Got 3V on pin 4 6 and 7 of LCD connector? Diode mode on those pins?
 

Laimis

New member
i have been reading a lot of forums and found out people with exactly the same issue. lcd connector pin4=3.3v, pin6=3.23v, pin7=3.23v. diode mode pin 4=280, pin6=570, pin7=570. I am thinking maybe i should try rewrite bios with clean me region as i mentioned in other forums that was the only thing that worked. Has anyone got a bios for this model?
 

dukefawks

Administrator
Do you have some donor boards? You can take the BIOS from a 2850 board for testing. Always backup your original file, the original ME has nothing wrong with it and should be merged with a working BIOS.
 

Laimis

New member
ok so i have tried to swap bios but no luck,still the same thing. i have managed to reset pram now but it didnt help either. it starts chimes but no video. all power seems to be there keyboard works. checked lvds ddc mux and LVDS_DDC_SEL_IG missing 0V. measured R9682-0V. Other required pulldowns has power but R9693 missing as well. Also checked Q9607 and pin2 ALL SYS PWRGD has power, R9676 pin1 has power but pin 2-0V. could you explain how it works? as far as i can understand when all sys pwrgd powers the gate it opens and lets GMUX_S3_PD_EN open the gate right? but now pin 6 and 5 0V
R9678 has power pin2 but 0V pin1 so LCD_pwr_en is 0V somehow. really struggling to understand why as pin 2 of R9678 is GMUX_S3_PD_GND so should be 0v i guess but now pin2 of R9678=2.64V, pin1=0V
 

dukefawks

Administrator
How are you testing with external screen? Was this board messed with already? Any history as these boards do not have video issue like this normally.
 

Laimis

New member
i have tested the screen on the another laptop it works fine. i have checked on external screen no video as well. originally it was water damaged. had 3 boards and all with the similar symptoms. what can possibly cause this? everything seems to work just LCD_pwr_en missing and i guess thats why theres no video .
 

dukefawks

Administrator
Are you sure this actually works without having OSX booted up? Try with a known good machine if it will display to an external screen without loading OSX.
 

iganas

New member
Good Saturday everyone, I have exact same board with seemingly same issue. No internal video nor backlight, boots, chimes, loads into OSX.

External video works fine.
Tried different LCD cables and different LCDs.

LCD_PWR_EN = 0.0V

Did anyone figure this one out yet?
 
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