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MacBook Air 820-3437 not working after backlight fuse changed

So I bought a 13” Macbook Air with an 820-3437 logic board that the owner said the backlight went out so he took it to a shop to have the backlight fuse replaced. Well I guess the shop replaced the fuse, doing a poor soldering job at that but also rendered the computer unresponsive. i get a solid PPV342 but PPBUS is oscillating between 8.6 and 7 volts. I hear a ticking sound around the SMC area. could that be shot even though I am getting PPV342? I am at a loss on this one.

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Not very uncommon that people selling faulty machines just tell part of the whole story. I doubt anyone with experience in component level repairs would replace a random fuse when the machine doesn’t even start up. It seems you have a faulty main power line there, PPBUS_G3H should have a steady voltage. Ticking probably comes from a faulty mosfet and it’s impossible to tell which mosfet it comes from just by the ticking noise. It may as well be a faulty U7000. No way to tell without isolating the problem, but replacing at once U7000 and the 5 close related FETs would give good chances to solve the issue.

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Thank you for your post. While I do agree with you on the point you only get part of the story, I think you missed the part where I said the person told me the computer worked before the backlight fuse was replaced. But since PPBUS_G3H is going up and down makes the whole backlight thing not on the front of the list, except for the fact that the pin 1 of the backlight fuse is tied to PPBUS_G3H. I can only assume that from this that the goon who soldered the fuse on may have done it with the power hooked up to the computer. I believe the ISL6259 is "U7100" correct? Thanks again!!

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@pati3ntzer0 I didn't miss anything, infact I expressed my doubts about the possibility a simple fuse replacement would kill a mosfet that's behind resistors which are there exactly to prevent that a short on a backlight circuit kills the entire machine. It's just a professional opinion, I don't know the truth. Of course if the repair was done by a random clueless guy anything is possible. And yes, the IC is the ISL6259.

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