9710 VCA 19
000216
A problem here most likely involves IC4, Q3, Q4 or associated parts. IC6 might be a problem,
but sections of it are working OK in the VCAs so the chip is most likely good. Check front panel
wiring involving J3 and J6. If you don't find anything, continue to the next test which may help
localize the difficulties.
5) Connect a second signal source to the
CVa (Mod) input and listen to the A output
for a balanced modulator sound while the
relative frequencies of the two sources
are varied. If you're not sure what Balanced
Modulator should sound like there are .wav file
samples at
http://paia.com/9730.htm
.
If this step checks out OK but step 4
didn't, you should suspect the expo
converter, which comprises Q3 and Q4
and the parts around them.
If this is not working and there was also
a problem in step 4 the culprit may be IC4 or
the parts associated with it. The Carrier input
buffer IC6:C or the differential output buffer
IC6:D may not be working.
If step 4 was OK but there's a problem here in step 5 there is probably something wrong
with the way J6 is wired.
6) Switch the modulator from Cycle to ADSR and connect a gate source to Modulation input G
(Gate). Gate signals should be "true positive" (transition from ground to a positive voltage
between 4 and 15V to trigger the ADSR). Set all the ADSR controls at about their mid-range
and activate the Gate. Either by listening or watching the LED verify that the output rises to a
peak level then falls back to a Sustain level where if holds until the Gate is removed then falls
back to 0. Try different setting of all controls from minimum (fully CounterClockWise) to
maximum (full CW). Change the gate signal from the Gate input to the Trigger input and verify
that the Sustain phase is eliminated.
Most of the ADSR circuitry has been verified while
using it as an LFO. If there is a problem now it most
likely has to do with the wiring of the J8 and J9 or the
ADSR controls R110 - R113 and the board components
directly involved with them.
Successful completion of these tests is a good indication
that the module is working properly.
( ) Gather the wires from the circuit board to the front
panelcontrols together and cinch the bundle with the
three Nylon Wire Ties supplied as shown in the photo.
Cinch the ties tight and clip off the excess.
