Bloody intonation

[badgermark]

It's still out  :?  Seems to be worse too, the low D string is now noticeably out of tune from the F note at the 3rd fret all the way along the neck. Really bloody annoying.

What can the main culprits be again? Intonation is dodgy, should I adjust the truss, action or what? Going to try troubleshooting it a bit more before i resort to taking it to a pro.

[WezV]

get a long ruler/tape measure and start to measure the scale length

use this handy tool:

http://www.stewmac.com/FretCalculator

chances are the bridge aint too far out if the intonation has been ok but its still worth checking