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Message: <blockquote data-quote="BSD Meister" data-source="post: 1415157" data-attributes="member: 257388">I'm a little bit leery of the idea that the sound cable was cut. An old, dishonest auto dealer trick: if the check engine light is on, pull the bulb or disconnect the cable - problem solved, or so it appears. If you accidentally cut the sound cable yourself, no big deal, but if the unit was beeping once in a while, one sure way to make that go away is to cut that cable.You can have several possible problems:1. PSU is defective2. Battery needs replacement3. Logic board is bad.If I were you, I would try to address the PSU's apparent problem first. They have a thermal cutoff switch in them and if it's bad or poorly calibrated, it will cut off prematurely. The first time I ran into this problem was in a lab. We used to have a facility with lame AC, and the temp would go from about 70 deg F to 78 deg F, then back down, and cycle like that. One unit kept erratically going out on us. I noticed every time it did it, I seemed hot, because it was. That temperature variation in the room was just enough to cause the faulty thermal regulators to shut off. You might have a similar problem. I know this might sound like a ridiculous idea, but put the PSU in a plastic bag and put it in the refrigerator for about 5 minutes (NOT the freezer). Take it out and try and power up the unit. If it will power up every time it's cool, then you've likely found at least one of your problems if not THE problem.I wouldn't go out and buy another supply yet without checking it out with one that's known to work well. I'd try to find someone you could borrow one from. If you have a local Apple/Mac users group, there may be someone there willing to help you out, or if you know someone in your area with the same type of unit.Make sure the PSU really is intended for your unit. Some of these "after market" units are actually factory rejects that have been repackaged and sold to unwitting distributors. Most of the time they're OK with minor cosmetic defects, but some times they're flat out rejects that have no business being sold. They're typically acquired from auction sites.I doubt this is it, but the battery might need replacement. It should be reading between 2.6 and 3.0 V. Also, make sure you haven't pressed on the unit's internal SMC reset button more than once sequentially because that can damage the SMC chip. If you have the unit open with the back of it closest to you, the SMC reset is on the far left side a little more than half way up the logic board. You don't need to reset the SMC because you're doing that anyway each time you pull the power out of the unit.I'm mostly concerned with the logic board. If that ribbon was broken by you, accidentally, it's no big deal, but if it was deliberately done because the unit was doing exactly what it's doing now, it might have been cut to "silence" it from warning a user that there's something wrong with the unit. If it is the logic board, it's likely a bad trace or solder joint in the logic board. Sometimes people unfamiliar with working on these units will attempt to upgrade the RAM and then crack some of the traces.  Unless you're really lucky these are almost impossible to isolate without special equipment. It would cost far more to isolate the problem on the board than it would to replace it.Based on what you've written, I think the most likely culprit is the supply.Hope this helps.</blockquote>

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