What does mean?


New member
  1. Disconnect power cable.
  2. Hold the power button on Macbook - Duration is not important, you can move to step 2 in a matter of milliseconds.
  3. Connect the power cable whilst still holding the power button.
  4. With the power cable in, keep the power button hold for at least 5 seconds.
  5. Release the power button.
  6. Press the power button to boot the Macbook. (THIS WAY MACBOOK BOOT)
A customer have this problem and what does mean? Usually SMC problem or could be more thing?


Staff member
That means there is a problem with some sensor, for current, or voltage; maybe themperature too (less probably).
Machine works in SMC bypass mode, when SMC doesn't read these sensors.
Check the schematic pages marked as power and thermal sensors.
Recently had this issue with SMC_BMON_ISENSE signal...


New member
Recived the laptop. It is 820-2496
17,18 and 27,28 are both 20 ohm.
No green light but when I touch the connector or connect and disconect the board green light appears for 2,3 segs.
ISL ACOK - 3.20V

Next is to replace the SMC?


820-2496 is ancient trash. Why replace the SMC, did you even diagnose the magsafe board? Of course you will need a green light for the machine to charge/turn on.


New member
I took the magsafe board from A1278 and same story. Green light appear only for few seconds each time I connect and disconect the ac adapter.