Join Date: Aug 2012
Location: West 'By God' Virginnie, USA
Re: Hardtailed RG1570z still has tuning problems!
My guess is the strings are binding on the nut.
The locking nut is made to stop the strings from moving at all, and even without the locks, there's a lot of surface area for the strings to slide over when bending, vibrato, etc. so it's not likely to return to pitch due to this friction.
You still have the fine tuners on the bridge, even though it's blocked. Tune up, stretch your strings, lock the nut, fine tune with the bridge and i'll bet it'll stay nearly perfectly in tune.
Unless there's some other issue, like a loose saddle or two, loose neck, etc. but I'm leaning towards friction at the nut.