Presuming you already have the item near the broken CRT, I recommend checking the note on the desk again, as that will lead you to a particular code for a particular lockbox.
If you'd like me to just tell you the solution to the puzzle I can as well.
As someone else who got stuck there, I'd say that puzzle needs to go or else it needs a secondary hint somewhere. Even with your hint I had to read the letter twice, minor typos just don't register unless they destroy the flow; if they did, nobody would make it through any comments on the internet.
