I have a 2005 Fender Showmaster that won't stay in tune. When I tune each string to a separate instrument, chords played lower on the fretboard are in tune, but chords played higher up on the fretboard are out of tune. When I tune only the low E string to a separate instrument, then tune the rest of the guitar to the E string, I have the opposite problem. Any ideas?
By the sounds of it, you have one of the following 3 options:
1. The intonation is out, would make total sense that the open strings are in tune, but up the neck a bit further, it would be out of tune.
To fix this, you would restring the guitar (you cant do accurate intonation with old strings), then plug it into an accurate tuner. Play the open string and get it perfectly in tune, then play the same string on the twelfth fret (note that the harder you press, the more sharp the note goes) and it should be perfectly in tune also.
If it is not in tune on the twelfth fret, you can adjust the intonation using the screw at the bottom of the bridge. If the twelfth fret note is sharp, you need to tighten the screw (making the string length longer)... if the note is flat, you need to loosen the screw (making the string length shorter).
Then repeat for all strings.
This is a really abridged version of how to do this repair, have a look on youtube, you will find directions there.
2. The guitar neck is too bowed, or the action is too high. If the neck is bent, then the distance from the string to the fingerboard will be higher as you go up the neck, meaning that when you press on the string to sound the note, the string has to stretch further to reach the note. You could adjust the grub screws on the saddles "down" to lower the action... neck adjustments, well, I would suggest finding someone who can either do that for you, or at least supervise you while you do it.
3. The fret scale is wrong... you would fix this by getting a new neck for the guitar. (this would account for waaaay less than 1% of all intonation problems I have seen, and it is unlikely to be this issue)
