Screen light inconsistencies: flickers at startup; randomly works full
My 2009 A1185 macbook screen has been working inconsistently for the last few days. At first I left it for several minutes and it went into sleep mode: I 'woke' it, however the screen remained black. With a flashlight I could see everything was functioning. The screen light was simply failing. I turned it off, took out and replaced the battery, plugged it into power and powered it back on. The screen worked! However, it went into sleep mode later in the day and the previous actions did NOT lead to a solution this time. I left it alone until it was fully charged and the screen then worked. I turned it off and the next day the light would flicker on powering up or waking from sleep, but it will not remain on.
Sounds to me like your inverter (or backlight) is going out. Essentially there is an assembly that sits underneath the LCD screen to give it light so that you can see. It might not be all the way dead yet, but the biggest tell is that you can still see the screen using a flashlight.
That link is for a broken cable, but you just need the full assembly, which are generally pretty cheap to buy $30-$40. If you buy the assembly and follow that guide you should be able to replace the inverter and get your machine back to normal.
If you replaced both the inverter board and the inverter cable with known working parts then there are three other parts that should be checked:
1- the top case (brightness control)
2- the battery connector/Sleep Sensor (sleep switch)
3- the logic board (inverter circuitry and that means a logic board swap)
1- To check the top case, disconnect it from the logic board and power on the machine via the two power pads on the logic board. If the screen works OK then the top case is faulty.
2- replace the battery connector/Sleep Sensor with a known working one.
3- replace the logic board