The oscillation equation for a singular string with discrete weight generated by a self-similar
n
n
-link multiplier in the Sobolev space with a negative smoothness index is considered. It is shown that in the case of a noncompact multiplier, the string problem is equivalent to the spectral problem for an
(
n
−
1
)
(n-1)
-periodic Jacobi matrix. In the case of
n
=
3
n=3
, a complete description of the spectrum of the problem is given, and a criterion for emergence of an eigenvalue in a gap of the continuous spectrum is obtained.