PLAN B analog blog

Jay,

I got your M15 back and the problem was not the morph out - the problem was both the 
triangle and sinewave output trimmers had been re-adjusted from factory setting so much 
they were locked up to the rails.  You were attempting to crossfade to DC and the morph 
circuit protects against that via a decoupler.

We test the VCOs three times.  The first time is right after the tempco and expo converter 
is installed, before the PCBA is mounted to the faceplate. At that point, we look to see if 
the core is oscillating, that the amplitude of the core signal is to spec and that the range 
via to freq pot is operating as it should.  It's a lot easier to repair problems with the basic 
functions at that point.

The second time we test, all of the ICs are inserted and we adjust the outputs to fidelity/
First the triangle symmetry, then the sine and lastly the sawtooth alignment. We also look 
at the VC inputs at this stage using a Tektronix FG501 Function Generator as the input 
stimuli.

These first two tests are done at the bench. The last one, where we calibrate thr 1V/oct 
input, is done on my system.  For this test, I monitor the morph out because it's one that 
can't be tested without the unit fully assembled and it enables easy access to all of the 
waveforms - sine, saw, square.  Note Triangle was not mentioned.  Given that the triangle 
output is a symmetrical version of the core signal, we don't need to test it at this point.  If 
it wasn't in spec neither the sine or saw would be working properly, which we do monitor.   
The improvement of the sine wave made on the rev. 1.5 PCB requires that the tri be 
perfectly symmtrical.  The 1V/oct calibration is done using a Novation Supernova II as a 
comparative reference, first playing in a midi keyboard, then using a Doepfer MAQ16/3 
preset which arpeggiates through octaves and fifths over the entire 127 step range.

We could not have shipped this unit with the triangle and siine trimmers out of 
adjustment.  And the trimmers on this PCB  were way off, not just a bit.

It's all good however.  the unit is operaitonal at n/c to you.
- P