Have you tried running voltage into the 1/volt oct jack to slow it down? If
that works, and the FM works correctly, you have narrowed the list of
potential problems down to a very few.
Four things are summed together to control LFO rate.
1 - 1 / volt per octave input (through R80)
2 - FM input (reversing) through R4
3 - rate pot (through R5)
4 - (-) 15 VDC through resistor R6 (fixed)
It sounds to me like the negative voltage connection to the rate pot is
broken, or as Paul B. suggested, maybe the pot itself is open internally.
But somehow, it seems that the negative -15 volt is not part of that pot
circuit any longer.
Measure voltage from the wiper (pin 2) of the pot to ground. You should be
able to see a voltage range at pin 2 of -15 to +15 volts. If my suspicion
is correct, you will see a range of only from +15 to about +10.5 (if my
quick math is right). Anyhow, it will be a much smaller range than normal
and skewed was toward the positive (or fast) side of the LFO range.
If the voltage is good at the pot wiper, then check the connections at both
ends of R5 and R6 for breakage (they are both 243K resistors near the left
top of IC # TL074. But, I am like Paul B. I think the likely candidate is
either the pot is broken internally, or the -15 volt connection is broken
where the pot solders to the PCB. Those are more likely candidates
That's my 2 cents from looking at the schematic.
Larry H
----- Original Message -----
From: scottgibbons23 <scott.gibbons@...>
though, except for the 320 LFO. It's range has become very
narrow using the "RATE" dial. It's slowest rate seems to be
about the same as the FASTEST rate on the 101. FMing the 320
with the 300VCO at a low setting brings it down to a useable
rate...