Intonation problem : half step down

[Inconnu]

Hi there!
This is my first post!
I just acquired a very old bowl back mandolin and I’m experiencing something unusual. One of the two highest strings, when fretting the first fret, sounds like the open string, then all the following frets sound pretty much a half step down from the other fret.

Any idea what I can do to solve that issue?

[CBFrench]

maybe this will help

[John Kelly]

From what you are saying, it sounds like the first fret under the affected string(s) is very slightly high. This would mean that when playing the open string you are actually playing a note that is in contact with the first fret; when you finger that string at the first fret you get the same pitch. If you are new to mandolin and its set-up get someone to have a look for you. This fret would need to be dressed to lower it very slightly, or perhaps, as it is a very old instrument, the fret has just loosened in the slot and can be glued down again with carefully applied CA glue. It is hard to give you solid advice when the instrument is not actually here in front of me, but I hope this might help.