which BBD? doepfer make a variety iirc...
I would set up the simplest possible patch
a vco into a vca into mixer - check that this makes sound (make sure that the volume is up etc)
then patch bbd in between the output of the vca and the mixer
make sure volume is up on correct channel and then play a single note with the vco - ideally very very short - as minimum delay time is 10ms - so make sure you have a noticeable delay time dialled in
make sure level on delay is not 0 - keep increasing this until you can hear the delay or have run out of travel in the knob
make sure that mix is past 12 o'clock - increase this if the previous step
another thing to do is to check the board components for signs of damage - burnt bits, bad smell, sticky residue - post pics (hi-res)
one other thing to note with doepfer modules - I have one that had the power cable on the wrong way (and not one that was just pull it out and switch it as it is connected to multiple boards) which would have been fine with unshrouded headers (which doepfer at least used to use) - but as I had shrouded ones I had to cut the key off the header to get it to fit - make sure that the red-stripe is correctly situated on both ends of the power cable
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities