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The backlight on my MacBook isn't working, but the fuse that says P has continuity when I test it. Am I correct in guessing this means the issue is NOT this fuse being blown?
Is this a good question?
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If you measured it correctly that is what I would assume!
Did you note the voltages? From side to side or just run continuity across?
If you’re not getting voltage on the hot side then you need to dig into the backlight power circuit.
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I just measured continuity across. My knowledge of "measuring voltage" starts and ends with putting the leads of my multi metre on either side of a battery to give you some idea of my lack of experience level. As it is I think my next move will either be "pay someone certified to diagnose" or "wait until I have my certification", but I appreciate the feedback that tells me I know just enough to realize I don't actually Know What The Problem Is.
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@bellavulpa it's actually not a bad repair. Here is something that sounds so "complicated", but it's actually straight forward. Start by measuring the voltage after backlight diode or on the LVDS connector pin 21 and 22. All voltages are VDC
If backlight is 45V or more there is no load on the backlight circuit. In that case you need to use a known good screen and check the screen connector.
If backlight is 25V-40V then the boost circuit is working. in that case you need to check the display connector, display cable, and the LCD.
If backlight is around 12V your boost circuit isn't working. Check the feedback trace, and the LCD driver,. Make sure that your BKL_Enable is working :-)
If backlight is 0V then you need to check for short. The LCDBKLT_FET, fuse, and enable transistors are the components you would want to check.
You can do all of this with just a voltmeter and some patience. This is on the assumption that your logic board is a 820-3115 based on the computer model you picked as your device.
If you want to give that a try, just post some images of your logic board. Very well focused, both sides and large enough so we can point out some of the components. Adding images to an existing question
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