This is not a master level trick here by any means, but it is one that caused me much confusion until i figured out what was going on. – Why i could use the exact same steps to convert one logo to black and white and yet sometimes, those steps wouldn’t work on another document!
I found out why – cmyk vs rgb.
To do these steps, you’ll need Desaturate (SHIFT + CTRL + U)
You will also need Curves (CTRL + M)
Now use the curves palette and drag the the line up to the top left.