Released June 2012, Model A1278. Intel processor with Turbo Boost, Up to 512 MB DDR5 Video RAM

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Exposed trace?/copper around R5410

820-3115 - B. Green light on charger but won't power on, no fan. When I first plugged it in I noticed smoke coming form under the heatsink so I took it off and started inspecting, which didn't take long because I found some exposed copper staring me in the face. I found a board view and schematic and believe this to be R5410. Any advise on how to proceed would be greatly appreciated.

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Does the resistor have continuity?

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Yes it does. I assume it'll need to replaced. Curious what to do about the exposed board.

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Very common issue in this area, have 3-5 3115's with exactly the same issue. A lot of the time, there is a short to ground inside the board, but sometimes PPBUS_G3H gets shorted to R5347 (low resistance to ground), which pulls PPBUS to ground. In your case, it looks to be the latter, but measure for a short to make sure.

The 4 vias the left of R5410 should not be attached to the area to the left of the resistor (spotty area) or the resistor itself. You may be able to separate these areas by digging slightly, mainly around the bottom via since it is likely joining to this area under where it is burnt (which would have merged the board slightly).

If you need to dig more than 2mm, I would advise against repairing it, it can be a potential fire hazard and you can usually see the board spark where the voltage is too close to ground. If you can cut the trace to separate it enough however, definitely worth repairing.

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Great input. I am fairly new to component level repair. I've swapped caps and an lvds successfully but it's the first time I've run into something like this. I bought a few bad boards just to practice on, this being one. Hoping I'll get the satisfaction of seeing this boot.

I'm somewhat confused about what this region is doing. I understand it's a current sense resistor and what that does but it's the first time I've seen the extended pads? On the boardview it shows this in a horizontal orientation with four pins. Are the two middle pins the soldered pads? And the outer pins the surrounding copper?

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In the board view it lays out the component wrong, there are 2 solder points, but each side has 2 different pathways, so it basically splits. It is for current sensing and the resistor itself has very low resistance, so a short on one of the points will short every other point on the resistor, for example, PPBUS_G3H.

The exposed copper is where the solder mask has come off, it shouldn't be like that; probably happened due to it burning. IIRC the 11 black spots to the left of this resistor is roughly where 12.6V runs through the board, and the 4 vias to the left of this paths around the resistor toward the right, which is why this commonly shorts PPBUS_G3H to ground in this area. You'll have to dig into the board to work out what has merged together and which traces go where

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Thank you so much for the clear and detailed explanation. You're freakin awesome. As far as the burned solder mask I assume I should fill with epoxy?

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You don't need to, but if you manage to fix it you can do

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Marc will be eternally grateful.
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