Hammond Organ L-100 Series, Service Manual

Page: 23 / 87

Page 23
charged through R6. This charging time is long enough to delay
the conduction of Q3 until after the first pulse; then Q3 conducts,
cutting off Q4 before the second pulse can be passed. Effectively,
each time a signal is applied to the input at T4, one pulse appears
at the output terminal (T11), which connects to terminal F of voice
generator board 124–000114. Q115 is normally off. The input at
“F” is fed through R163 to the base of Q115 to turn the transistor
on. When Q115 is on, the DC voltage at its collector drops from
+15VDC to 0VDC. Note that pin “G” is jumpered to pin “C”, and that
both are common to Q115’s collector.
The signal altering pin “C” is fed through R160 to the base of Q114,
which is nor mally in the “on” condition with no pedal pressed
(collector at 0VDC). When a pedal is pressed, the negative signal
applied to the base turns “off” Q114, and the collector voltage rises
to +15VDC.
Point “D” is routed to point “A” and coupled through C127 and R156
to the base of Q112. Q112 which is normally “off” is turned “on”,
and its collector voltage drops to zero. The collector signal of Q112
is then fed to the base of PNP Q113, turning it “on”, and its collector
switches to +15VDC.
This +15V DC pulse on the collector of Q113 is desig nated as
the pedal-down pulse, and is routed through the BLOCK and/or
CYMBAL tabs, when “on” to trigger the selected voices. Output is
obtained as described in
2–8–2 Push Button Circuits .