Ok so first of all, my buddy has an Epi LP Custom, and this thing is completely screwed up. His action is VERY low which is causing a lot of fret buzz, but obviously I told him to raise it. There are spots on the fretboard where you cannot bend at all or the note goes mute. I wasn't sure if that was b/c of the action or not but there's the first problem. The second: there are spots on the fretboard around 16-20 on the G, B and high E strings where the note is exactly the same. For example, say I play a note on the 16 fret on the E string, and move my fingers to 17, 18 and 19, the note is the same as it was on the 16th. Is this a truss rod problem b/c that's what I thought of first, or will all that be fixed by raising the action to a normal level, b/c it is VERY VERY LOW.?
sounds like the neck could be out of alignment, or something with the frets. bring to a shop dont mess around

Epi Les Paul Std w/Duncans
Cry Baby From Hell
Marshall JH-1
EHX Metal Muff
MXR EVH Phase 90
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Ibanez LU-20
Dunlop DCB-10
Crate V50112
Tascam US144

yeah, bring it to a shop and let them do a set-up.
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This happened to a friend of mine, his action was way too low so fretting notes would often just fret the highest fret(21), instead the desired note. highering the action should fix this and also the problem with the notes dying out. If that still doesn't work you may need to adjust the truss rod.
Raise the action first, its a dead simple task, if this doesn't work, adjust the truss rod (carefully), if this doesn't work, take it to a shop, it may need some work done on the frets.
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