I recently bought a new non-weight relief Gibson les Paul standard with 50's neck. The guitar comes with an ABR style tune-o-matic bridge. As soon as I played it I noticed that the low "E" and "A" string had intonation problems. They both sounded flat when pressed at the 12 frets. So, I checked the basic set-up of the guitar, the neck relief and the action, which were both perfectly set. Hence, I decided to intonate the guitar. I adjusted the bridge saddle by rotating the screws toward the neck. The low "E" got intonated but the "A" string is still sounds flat with the bridge saddle at its maximum forward position.
I tried to raise the action, which compensated a little but the "A" string is still flat. I then tried to flip the saddle opposite way yet the "A" string still sounds flat when fretted at the 12th fret. I simply am not able to intonate the “A” string.
I would really appreciate your help and suggestions to fix this problem.