Elektor Formant Modular

Hi.
i just set up my formant after years of pause.. it needed a new house:)

there is a problem:
the 12 db filter doesnt close completely.
i can adjust p7 so the filter closes, but then the freq knob doesnt go
"all the way" up.. that is, the input signal is being filtered a
little bit even though the filter is completely open. or the  filter
opens up completely but then it doesnt close completely.

any suggestions?
thanks!