gnrnld, besides a bad connector on the logic board, like Nathan Barnes suggest, there is still the possibility of a bad inverter circuitry (the LED driver), a bad backlight fuse, as well as a multiple others:-). Here is what Apple suggest to do first :-)
No Video/Bad Video
Unlikely cause: hard drive, optical drive, top case, battery, power adapter
Symptom Quick Check
Power, but No Video
• No video
• fan, hard drive spin, or optical drive reset sound
• sleep LED is on or went on
• light if Caps Lock pressed
1. Reset SMC.
2. Reset PRAM.
3. If no startup chime, verify with known-good memory.
4. Verify with external monitor.
5. Press Option key on startup.
Check Result Action Code
1. Characterize video issue Define whether the issue is a bad image with backlight OR no video issue. Verify whether some image even distorted is visible.
Yes Bad image quality,
go to step 5.
No No image seen or no backlight,
go to step 2.
2. Isolate peripherals as cause: disconnect all peripherals, external devices, Express Card and display adapters if present and verify that video is displayed.
Yes Suspect peripherals as cause.
Reconnect one at a time, verifying unit operation at each stage.
No Go to step 3.
3. Adjust Brightness Power-on unit , attempt to adjust brightness to maximum using brightness (F1/F2) keys and verify that video is displayed.
Yes Video displayed - Brightness set to minimum, panel backlight was inadvertently turned off. If backlight returns to low check for stuck F1 key on keyboard.
No Go to step 4.
4. Reset SMC and verify that system video is displayed.
Yes Corrupt SMC state preventing video.
No Go to step 5.
5. Reset PRAM. If no action, use external keyboard with same sequence. Verify that system video is displayed.
Yes Invalid or corrupt PRAM contents affecting video output.
No Go to step 6.
6. Connect external video:
Connect known-good VGA/DVI adapter to known-good display, press power button and close display to force main screen startup on external video. Verify that video is correct when displayed from external display.
Yes Video correct on external display. Research available firmware and software updates, retest. If returning with software already updated, go to step 7.
No Replace logic board with according symptom code:
7. Isolate LCD display detection:
Disconnect external monitor and reopen display and restart unit. Verify that sleep LED indicator goes off after internal LCD has been detected.
Yes Sleep LED goes off when LCD detected.
-If still no video then Go to step 8,
-If video present, but with defect, go to step 9.
No Internal LCD not detected.Run Clamshell Service Diagnostic utility and check for LCD panel presence. If not found, reseat LVDS cable connection on logic board and retest. If sleep LED does not go off after cable is reseated, go to step 10.
8. Check for sleep sensor condition. If display assembly sleep sensor is stuck in a closed state, video will appear on internal display temporarily, until the OS sleeps the system. Disconnect BIL/ sleep cable and restart unit without external display. Verify that system starts up with video on internal display stays on and does not go into sleep mode.
Yes Sleep sensor was stuck or had shorted cable. Replace BIL/sleep sensor cable.
No Symptoms unchanged.
Go to step 9.
9. Check for No Backlight. Power on unit. Using a lamp or bright light source, verify that a faint image or Apple logo appears.
Yes Logo image visible - check LVDS cable. Inspect cables for damage near clutches:
- if damaged, replace display assembly and go to step 11
- if cable is not damaged, run Clamshell Service Diagnostic utility and check for LCD
panel presence. If not found, reseat cable and retest, then go to step 11.
No If symptom continues, go to step 10.
10. Verify with Known good display assembly Connect known-good display assembly to system.
Yes System is functioning with known-good display assembly. Replace display assembly if following symptom reporting:
- had no power issue
- had incorrect/missing colors
- had blank video
- had distorted / blurred video
- had vertical/horizontal lines
- had noise/unstable flickering
- had dim backlight
- had bad spot(s)/pixels
- had no backlight
- could not change resolution
No Symptoms unchanged - replace logic board.
11. Verify with reseated LVDS cable or replaced display assembly Verify that unit now has video and backlight.
Yes Issue was only due to damaged display assembly or unseated cable.
No Display cable damaged the logic board. Replace logic board."
Here is the pinout for the LVDS connector, and there are only a few that you can check with a multimeter:"
1 GND Ground
2 Vcc Power Supply (+3.3V)
3 Vanalog Power Supply (+3.3V)
4 VEDID DDC Power +3.3V
5 Vsync Vsync
6 ClkEDID DDC Clock
7 DATAEDID DDC Data
8 Rin0- Differential Data Input
9 Rin0+ Differential Data Input
10 GND Ground
11 Rin1- Differential Data Input
12 Rin1+ Differential Data Input
13 GND Ground
14 Rin2- Differential Data Input
15 Rin2+ Differential Data Input
16 GND Ground
17 Clkin- Differential Clock Input
18 Clkin+ Differential Clock Input
19 GND Ground
20 NC NC
21 Vdc(1 &2) LED Annold (Positive)
22 Vdc(3&4) LED Annold (Positive)
23 NC NC
24 Vdc1 LED Cathode (Negative)
25 Vdc2 LED Cathode (Negative)
26 Vdc3 LED Cathode (Negative)
27 Vdc4 LED Cathode (Negative)
28 Vdc5 LED Cathode (Negative)
29 Vdc6 LED Cathode (Negative)
30 NC NC
Of course you also want to check the backlight fuse It is a 3amp - 32V 467 packaging fuse. Check with an ohmmeter for continuity. Last but not least, it could be the LED driver LP8543SQX/NOPB-ND Datasheet is available right here. If you can attach top and bottom view images of your logic board. We can probably show you where those components are located. I am not a Mac person, and I am sure the real gurus can figure it out better than I can. Hope this helps, good luck.