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I have a Thinkpad T60 and this morning it started acting up. When I plug it into the AC adapter, the AC power light comes on for about four seconds, then goes off, then comes back on and simply repeats this cycle.

Is there a way to diagnose that this is a bad AC adapter or bad battery?

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Also, here is an amazing resource on learning about power adapters: repairfaq.org/sam/aapsfaq.htm –  CamelBlues Apr 4 '13 at 14:16
    
Does the computer boot? –  Xavierjazz Apr 4 '13 at 15:13
    
@Xavierjazz yes –  CamelBlues Apr 5 '13 at 15:25
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1 Answer

Remove the battery and then try with the AC adapter connected.

If it persists with only the AC adapter connected, replace the AC adapter. It sounds like the adapter is not providing the correct voltage to the laptop. The AC adapter may be wearing out or it may be a third-party adapter of questionable quality.

If you had a professional battery tester you may be able check the battery voltage to be sure (a local battery store or laptop repair shop may be able to do it). Without that, replacing with a known good battery to test is really the only way to be sure.

If the battery is bulging in any way then it should not be used anymore and replaced.

Failing components like a stuck fan, bad motherboard, or bad RAM could cause similar behavior. Could moisture have entered it? Check all ports and look for corrosion - if you find this you're likely looking at replacing the motherboard.

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Agree sounds most like an failing battery, either to old, or a cheap china clone battery. Testing it would be usefull, and could be done quick. –  Psycogeek Apr 4 '13 at 17:46
    
Whoa, this a great answer. I'll try this when I get home –  CamelBlues Apr 5 '13 at 15:25
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