Each letter corresponds to a different problem, but the only serious one
is “A” since it indicates that the VCO can’t be sensed by the CPU, either
because it is very low in frequency, has a DC offset on it, or is completely
missing.
If you get other letters coming up, they usually go away after the second
or third time you press AUTOTUNE. This is because it’s possible that the
CPU didn’t get the right reading on the previous try, or that the
instrument isn’t warmed up yet. Persistent letters indicate a true VCO
problem.
If any letters are displayed, the CPU will disable the voice in which the
defective VCO resides, so that the instrument may still be played with
one less voice until it can be repaired.
3.4 DC
Voltages
The card uses +/- 15V to drive the CEM 3340s and opamp ICs. The
CEM 3340s also require a stable -5V reference, which is derived on
board to minimize system interaction between cards. The +10V reference
from the DAC is also used on this card to provide a current reference for
the CEM 3340s.
3.5
Card Pin Signals
The signals coming into and out of the card are as follows:
3.5.1 Inputs
Modulation inputs for the VCOs coming from the VCF CARD
+10V reference from the DAC CARD
Power supply /- 15V and analog ground
CPU control signals for the CD4051 demultiplexers (Enables and AL0, 1,
2) coming from DIGIMOD
DAC control lines (SAW, TRI, SUB, FM, SYNC)
Pitch bend input from ANAMOD 2
Multiplexed DAC signal for 4051s
3.5.2 Outputs
VCO1 & 2 outputs for two voices
3.6 Troubleshooting
Tips
These troubleshooting tips assume that the VCO test tape REV 1.0 has
been loaded into the VOYETRA. If this tape is not available, the
