Back light not functioning
Cleaned my screen last night. Unfortunately (?), I used eyeglass cleaning spray that I had sitting near by and have used before, although it tends to be thinner and run more than a traditional LCD cleaner. Shortly after, the screen went black. I am afraid some of the cleaner may have slipped below the black clutch cover at the bottom of the display and is shorting the back light strip or even caused a fuse on the board to pop.
I can see my desktop and application windows when shining a light through the apple logo on the back of display. So, obviously the display is getting the video feed, but not being back lit.
External monitors work fine via HDMI. Changed the automatic graphics switching settings to try to determine if the problem is the dedicated GPU. No change or affect. In fact, I can still play games at 60fps or better at high resolutions, so I have a feeling the GPU/logic board is ok.
Attempted the usual NVRAM and SMC reset, but to no avail. Left the display up and the computer powered off overnight, hoping that perhaps the liquid would dissipate if that is what is causing the problem.
Ironically, I also installed a security update yesterday, but that was about 12 hours before the back light went out.
Any help would be greatly appreciated. I am handy with electronic repair, so just need to know where to go from here.
I ran Apple Diagnostics and "VFD002" is returned. Not ground-breaking by any means as it tells me what I already know: that something is wrong with the display. Thought I would include this info anyway in case it proved useful in some way.
And one additional update:
I have read that Apple's security update 2018-001 is causing similar problems for others on OS 10.11. However, after I booted from a cloned 10.9.5 drive I still have sitting around, the back light remains off. So, my problem is definitely hardware related.
I have been using the laptop as a desktop since the malfunction and have had no issues other than the battery swelling up, requiring replacement. But since I am a stubborn man, I am going to try to fix it.
I already own a dissecting scope and have acquired the schematic and boardview file for my board (820-3787-A). I replaced the backlight fuse which was definitely blown. Even with a working donor display, the backlight still wouldn’t turn on. Upon further inspection I noticed a hole in the top of the LED control chip (U7701). Obviously it exploded! So I ordered a hot air rework station and removed the chip. I was going to put the new one on, but noticed some dodgy looking resistors and capacitors. So that leads me to a few new questions based upon the schematic.
- Many of the resistors are marked TF. Are those thick film or thin film resistors? Does it matter?
- Likewise, there are some resistors marked MF or MF-LF. I am assuming MF = Metal Film. Correct me if I am wrong. What does the MF-LF stand for? Looking on Mouser, etc. I do not see any resistors of that type.
- There are several capacitors marked with package size 402-2. I know what a 0402 package is. And I know this is still indicating an 0402 package. But what is the “-2” part of the package? I am assuming a specified height, but once again cannot find an actual package specified as such.
- At the top of the schematic page for the backlight circuit I see the following in the page notes: BKLT:ENG - Stuffs 10.2 ohm series R for engineering builds | BKLT:PROD - Stuffs 0 ohm series R for production. Several resistors on the schematic are marked as “BKLT:ENG “ and 10.2 ohm resistance. However, since this is an actual production model, would I replace those with 0 ohm resistors if need be or stick strictly to the schematic designations?
Probably have more questions to come, but those are the most important at the moment. Any help would be greatly appreciated.
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