Grabbed out my old unused White Macbook 13" Mid 2009 (Macbook 5,2) because I'd like to donate it to someone. However, it wouldn't power on or charge (no light on the MagSafe adapter).
I worked out that if I first connect the MagSafe adapter to another Macbook (a 13" Macbook Pro) and then plug it into the 13" White Macbook the green light turns on with White Macbook 13". So it would seem that the White Macbook isn't completing the handshake but the MagSafe adapter works for a while after the handshake is completed on another Mac. This is all 100% reproducible.
Anyway, the Macbook still wouldn't turn on (and the MagSafe indicator remains green - never orange). So I worked out that if I SMC reset, the Macbook will then proceed to boot. However, when booted it said "No battery connected" and the fans remain on high power constantly (i.e. the kind of stuff an SMC reset is supposed to fix).
If I turn the computer off it then won't boot again. I have to repeat the procedure i.e. MagSafe handshake with another Mac, then SMC reset and it boots.
I pulled apart the Macbook detached the MagSafe connector and cleaned some gunk off it. I then replaced the hard-drive with a brand new SSD that has Yosemite installed (instead of Lion). I then gave everywhere else inside and out a clean and reassembled. However, after reassembling the same problem persisted (SMC reset needed before booting).
After several SMC resets and boots, I've now got the Macbook in another state. The power is connected but there is no light at all on the MagSafe. However, the computer boots up. When booted fans are on again, but no power indicator of any sort is in my status bar (no battery, no DC power thunderbolt either). Disconnecting the power instantly turns the Mac off, so clearly it's really running off DC power.
The Macbook is running the latest firmware/SMC. When booted up everything actually functions fine aside from the fan - I'm typing on the Mac now.
Does anyone have any suggestions as to what could be wrong, tests to diagnose or ideally a solution? I'm reasonably handy with a multimeter so if anyone has some power diagnosis steps then I can follow along easily enough.
The process I was using to get the machine to boot was a bit flakey, however I've now narrowed it down to 100% reproducible sequence.
Disconnect power cable.
Hold the power button on Macbook - Duration is not important, you can move to step 2 in a matter of milliseconds.
Connect the power cable whilst still holding the power button.
With the power cable in, keep the power button held for at least 5 seconds.
Release the power button.
Press the power button to boot the Macbook.
Note: Having another Macbook around to plug the cable into is not important - all that seems to do is ensure the MagSafe light comes on, but it boots fine with the light off.
Now, when booted I have the fan and battery symptoms listed above.
I took the top off again and shorted the "SMC RST" (SMC Reset) pins on the board. This didn't resolve the problem, the behaviour remains the same. However, I've noticed a very faint ticking noise when I first connect the MagSafe cable to Macbook. It's very quite but there are exactly 8 ticks evenly spaced over about 2-3 seconds. This is pretty odd as the only moving part in the whole thing is the fans. Yet I hear this 100% reproducibly when I connect the power cable.
I'm presently waiting for a new battery I've ordered to arrive. Hopefully the new battery will shed light on the issue, or ideally resolve it!
Brand new battery has arrived. When I insert the battery and try boot, the machine will not boot. My usual boot process (outlined above) does not work with the battery present, I can not power on at all. The Magsafe connector's light remains off.
The machine continues to boot post SMC following the procedure above when the battery is not present. If I then insert the battery after the machine has booted, the laptop stays on. However, OS X thinks no battery is there. If I remove the power cord the laptop continues to "function" (i.e. full-speed fans) using the battery. However, there is no indication that the battery is being used in OS X, and when the cable is inserted there is no indication that it is charging (the Magsafe light remains off).