820-3115 no image

Got a 820-3115 board here with no display. It has the usual dirt and some surface corrosion for a board this age, but nothing too serious.
It will chime and I get usb activity, the screen gets energized(goes to deep black when booting) but never show a picture. Tried with a spare screen so it's definitely a board issue
I checked around the LVDS connector and L9008 was blown. Replaced with part from donor but still no image.
What should I check next?
 

2informaticos

Administrator
Staff member
Post voltage for pins 2/3, 4, 6, 7 of J9000.
If some voltage misses, compare diode mode reading with working board.

Be sure L9004/80 are good.
 
Sorry for the delay @2informaticos , put this one at the bottom of my queue for a bit. Here are the readings with screen connected:
pin 2 3.244v
pin 4 3.289v
pin 6 3.288v
pin 7 3.288v
All voltages seem to be present, and I checked the inductors have same voltage on both sides. Also R9008 and R9009 measure 10k almost exactly, so I'm not sure what to check next
 

2informaticos

Administrator
Staff member
Check if L9080 has practically short IN-OUT.
You can get same voltage, but high resistance can block bus communication.
Check BKL_EN/PWM levels.
 
L9080 has 1.3ohm through on both pins 1-2 and 3-4. Same as donor board I have, so I expect it's good.
BKL_EN and BKL_PWM both read 3.15V, measured near u9701. PPVOUT_SW_LCDBKLT measures 12.6V so it's not boosting, but I can't see any image shining a torch through the screen, even when booted into OS and working mirrored via displayport adapter
 
Replaced U9701 now, still no image or backlight
Checked continuity from LED_RETURN_1-6 pins on LCD connector to U9701 pads, all show continuity through resistors, pretty much 0ohm (or as close as my meter gets). Backlight voltage still 12.5V
Can U9701 cause no image? never seen that before
 

2informaticos

Administrator
Staff member
Image should appear BEFORE backlight.
However, as backlight signals are correct, you should get backlight now.

Did you check diode mode to ground on all return resistors?
Also check on video data lines.
 
Just came back to say all readings were close to known-working board.
I tried reballing SMC and now when the laptop powers on it no longer boots and I get one beep every 6 or so seconds. How did this happen? I've done quite a few SMC reballs before and never seen this happen as a result.
 
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