•
CPU control signals for the CD4051 demultiplexers (EN 15, EN 9,
AL0, AL1, AL2) coming from DIGIMOD
•
Modulation scan clocks (MODEN, MA0, MA1)
•
VCO multiplexer clocks (VMA0, VMA1)
•
DAC control line (Bypass)
•
VCO1 & VCO2 audio inputs for four voices from VCO cards
•
Noise input from MIXER
4.6.2 Outputs
•
VCO1 & VCO2 modulation outputs for four voices
•
Four VCF audio outputs
•
Multiplexed VCO1 & VCO2 outputs
4.7
VCF Card Troubleshooting Tips
These troubleshooting tips assume that the VCF test tape REV 1.0 has
been loaded into the VOYETRA. If this tape is not available, the
suggestions will still prove useful if the theory section has been
thoroughly understood.
4.7.1 Step 00-02: Resonance (Q) Tests
These steps check that the Q control is within a specific tolerance.
Problems may be caused by a defective SSM 2044, but the LM324 that
derives the Q control voltage should first be suspected. Note that the four
Q modulation outputs from the CD4052 U7 (and the four F
c
modulation
outputs) should all be at 0 V. Thus, Q calibration problems where Q will
not turn off should take this into account.
In steps 00 and 01 the F
c
output controls from U6 LM324 should be
about 2V on pins 1, 7, 9 & 14. As in any inverting opamp circuit, the
negative inputs, pins 2, 6, 9 & 13 should be at 0 V.
In step 02, pins 1, 7, 9 & 14 should have a sweeping sawtooth. Pin 13 on
the SSM 2044 should have a sawtooth of about 50 mV
pp
.
4.7.2 Step 03: DC Feedthrough Check
Ideally, the SSM 2044 should not have any output if no audio input exists.
However, if the IC is defective, changes in F
c
control voltage will reflect
onto the output even with no audio at the input. Thus, a square wave
control signal (derived from the F
c
mod system) is used to check for this
feedthrough. ICs which have an output square wave leakage of greater
than 1 V
pp
should be rejected and replaced.
4.7.3 Step 04-11: Initial F
c
and V/Oct Calibration
These steps all check for proper F
c
summing amp (LM324 U6) operation
by calibrating the initial F
c
setting, filter keyboard tracking (V/Oct) and
