Unstable C5 Grand

[Benny L. Tucker]

Hi list;
    I am soliciting the advice of you piano tuning wizards to help me solve
a tuning problem.
    Piano is a Yamaha C5 Grand, approximately 13 years old. In a large
Baptist Church . There are 2 electric guitars and electric bass, full drum
set and all amplifiers on stage and right behind the pianist. No humidity
control system on piano. The problem is in stability of the unisons, but
only in about a 1 or 2 octave area. It starts about 5-6 notes before the
capo bar/plate strut up to about 5-8 notes above this strut.
    Now I'm not talking about perfect unisons starting to whine a little,
I'm
talking about unisons slipping out very badly. I have tried every trick I
know,
and I just can't get it to stabilize for more than a week. The strings
"seem" to be
rendering over the bearing points good. The tuning pins are tight enough.
The pitch stays very stable on this piano, even without a DC system
installed. The piano is very bright and needs voicing, but the music
director
likes this bright sound.
    If this sounds like a hammer technique or string setting problem, please
respond with advice. I have tuned pianos all over the central Ga. area, and
never had a
call back, except for the recommended 6-month tuning. I feel my techniques
are good,
but any and all advice will be mostly appreciated. FWIW, I did lube the
v-bar in this area
with cpl, result=no help.
    Thank you for allowing me to post to this list, and I look forward to
many more conversations with you all.

    Benny L. Tucker