Hi i have a WD20EVDS DOM 01-2011.

The HDD doesn't want to start up. So i've checked the circuit board under the mircoscope.

The is a diode (D4) labeled ON 6LG R047 that seems to be bad, because it's continious in both directions. Might be a Zener diode, but i'm pretty shure it's not.

Any information on that diode would be helpful. Also with what diode i can replace it with; don't have a donor board.

Thanks

It's TVS diode manufactered by ON Semiconductor
https://www.onsemi.com/

It's a protection component, the purpose is to protect the rest of circuit from over voltages.
You might find interesting and useful FAQ about TVS diodes from fzabkar
http://www.users.on.net/~fzabkar/HDD/TVS_diode_FAQ.html

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My firmware database:
https://mega.nz/folder/O01DkBRI#MxP2J6ZNqXDcrX40I8MoQQ