[sdiy] Crap.. I need help with my x0x

[Jeff Farr]

The assembly in general has been going well, no screw-ups about placing the
wrong components or messing up the orientation. I've even gone over the part
list for each section twice now, carefully checking that what was in my
board was correct. The VCO works fine and the VCF works.. but rather poorly.
It seems that even with the cutoff all the way up the signal is being
filtered, and the cutoff doesn't track along with the VCO, even so I can't
create a note that's low enough to see a clean saw or square. Turning the
env amount knob up causes the cutoff to drop, perhaps this is normal?.
Again, I've checked *very carefully* *twice* *each* component and it's
orientation using a magnifying glass and a bright halogen lamp. They are all
correct, each resistor, capacitor and transistor, and they were all correct
the first time I soldered them in. Now, leaving the VCF behind the envelope
appears to be working as proper. Measurements at D35 and 36 agree with what
is listed in the fab manual and the VCF will respond to triggering the
envelope, but I'm doubtful that the decay is working as it's quite snappy at
either end of it's range. Still, I pressed on and assembled the VCA and here
is where things get discouraging. No signal at all while performing the test
from the manual. In fact I don't understand why I would be using R10 to
generate a pulse when before I was using R3 (using R3/R146 the VCF will
respond). Measuring R10 certainly didn't show 10V, and it was part of the
pre-assembled USB section, so I'm wondering if this is an error in the
manual. Now, I would like to know if I can test the difference between the
VCA being triggered and the VCA working. In fact the signal from the VCF
disappears after C21 and R121, after that all I can read is 5V, almost
everywhere in the VCA circuit. I need some advice on this. I don't
understand how the filter works well enough to break it into an input stage/
output stage and definitely don't know what I would want to see anyway and
the VCA has me completely lost due the the mystifying BA6110 in 9 pin SIP
for which I can't find a datasheet.
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