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I have a Harley Benton SC-550 (Les Paul style) with a strange intonation issue which affects the top 3 (unwound) strings at frets 20 & 21 only. The pitch at fret 20 is a whole semitone sharp, and the pitch at fret 21 is exactly the same as at fret 20 (i.e. there is no change in pitch when moving from fret 20 to 21).

This applies only to the top 3 strings (G,B,E), all of which are unwound. The bottom 3 strings are fine. The frets are all in very condition, with very little wear.

I've tried adjusting the intonation of the top 3 strings, turning a screwdriver ant-clockwise to move the bridge saddles further away from the neck, but it has made no difference.
Any idea what the problem might be, and how to fix it?

Harley Benton SC-550 Bridge

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It sounds like you probably have one high fret, causing it to choke the string.

Strictly speaking, you need a fret rocker to test for this, but any good, solid short straight edge can be pressed into service.

enter image description here

Pic Sweetwater

If you do find one is high, then I'd be inclined to take it to a luthier rather than attempt to DIY it. It's a fine-tolerance tweak you don't want to get wrong.

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  • The OP can try to confirm this by increasing the action of the strings (to have them higher, eg more distance from the frets) and the problem should disappear. But yes, if the 20 does not make difference with the 21, it's probably that the 21 fret is too high
    – Kaddath
    Aug 8, 2023 at 7:44
  • Many thanks for the feedback - that sounds logical. To my untrained eye, it looks more like fret 20 is too low, rather than fret 21 too high, but I could well be mistaken. Sounds like good advice re. taking it to a luthier, although I'm not sure whether it will be cost-effective to have it rectified! i.imgur.com/kvkmpX3.png Aug 8, 2023 at 11:24
  • I can't really tell anything from the photo, even after sharpening it up a long way in Photoshop. You need the straightedge edge-on, actually touching all the frets in the area you're examining. That looks like it's laid flat, so it's floating off the frets at the edges where we can see them. That's why you really need the rocker too, you can set it just to three frets at a time & literally feel it rocking over a high fret.
    – Tetsujin
    Aug 8, 2023 at 11:51
  • OK I just rested the edge of an action gauge on the 21st fret and it definitely rocks over that fret. Any idea what a luthier might charge to fix that sort of thing? Aug 8, 2023 at 12:21
  • I've no idea, sorry - will likely also depend where you live.
    – Tetsujin
    Aug 8, 2023 at 12:41

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