Just spent a fruitless hour fiddling with my bike but am completely stumped.
I'm working with deore shifters and LX 9 speed mech. Shifting was a getting slow and random so I lubed the outers, reset the barrel adjusters to the middle of their movement then fitted a new cable.
Now I cannot get all 9 gears, the mech refuses to shift to the smallest sprocket, if I then turn the adjuster on the mech it will move down but that then stops me getting into the largest sprocket.
I've started from scratch again and it still won't work! Never had this problem before.
Any tips?

Go to YouTube and search for derailleur gears. There are loads of vids on how to do it.

Have you adjusted the limit screws?

Cable is too tight?

The problem I had with mine was it would jump 2 sprockets at the top going up and 2 at the bottom going down but only at the end of the travel, not the start. If that makes sense?

limit screws are set correctly…previously the shifting included all 9 sprockets but wasn't very slick, due to cable wear (or so i thought)…so fitting a new cable should have cured the problem witout any further adjustments.

seems I was wrong…

cable goes ever so slightly slack when shifter is in 9, but chain won't move down to that sprocket…but the mech has the potential to move that far if you know what i mean?

As tbc says sounds a bit like limit screw adjustment is required, just try 1/4 turn each time. Try going to the Park Tool Site they have a great repair help section, I used this to completely build my bike.

If there is slack in the cable when you should be in your smallest sprocket, but the rear mech isn't moving that far, then I would say either:

-limit screw not right
– bent hanger/mech/frame
– stiff mech parallelogram not allowing spring to pull it all the way to smallest cog??

Loose mech / hanger bolt?