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  1. #1
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    Test logic board fan and circuit

    I am working on an 820-2879 board to just gain some practical experience. The fan is not coming on but there is 5v at pin 1 (PP5V_S0) I see that it is PWM controlled and there seems to be a voltage divider, a FET and presumably the SMC involved in it's speed control. Any clues on how I might determine if it's the fan itself or the speed control circuitry that is at fault please.

  2. #2
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    Re: Test logic board fan and circuit

    all_sys_pwrgd is missing. find out why

  3. #3
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    Re: Test logic board fan and circuit

    Hi and thanks for that I'll check for that signal. Cheers

  4. #4
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    Re: Test logic board fan and circuit

    Is the board powering up and chiming?

  5. #5
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    Re: Test logic board fan and circuit

    I initially thought that this board would have the fan running with just just being in a state where the green LED was on (like the 820_3330) but apparently I needed to turn the board on by momentarily grounding SMC_ONOFF_L I had the heat sink off seeing as I was probing there for various voltages and signals during the diagnostic process and once I turned it on the CPU and MCP where warming up and the fan was working. So the next step is to refit the heatsink, connect a speaker and screen and see if I have a chime and image. I hope to do that later this evening and thanks for replying.

 

 

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