Is that the EQ700 7-band pedal? If so, I have one of these that I bought for use in the effects loop of a Vox AD60VTX modelling guitar amp, to beef up the dynamics, which worked quite well ...
I just tried it in the effects loop of my Markbass LMII and it works fine, down to low B, on all bands — did you try yours in an amp's effects loop or inline with the input? Or with a guitar amp? (I should add I've used mine similarly with two or three different all-valve guitar amps and it worked well, considering it's a budget pedal).
Which were the two frequency bands you found to work? Just trying to ascertain whether yours really is duff, or not?