3M DELTA Series - Bias Generation

solenoid; and a low on pin 33 to turn on the RUN
lamp. Likewise, the "READY" line goes high to extin 
guish the READY lamp. The processor also outputs a
100 millisecond low on pin 29, the AUX START pulse
line. This line is a user line and may be used to
remote start or reset an auxiliary piece of equip 
ment such as a turntable or timer. All other circuits in
the Delta logic work in a similar manner.
IC's on the logic board are bypassed with . 1 mid
capacitors. An on-board 47 mid electrolytic is used
to decouple the +5 volt coming in from the power
supply. At power up. the microprocessor is reset by a
pulse from PIN7 of U2 17. This pin will stay “ low" for a
brief time after power up until voltage comparator
U2 17 toggles as the +1 4V power supply initializes.
During machine operation, U201 pin 11. (ALE),
outputs a pulse train that is 1/ 15th the master clock
frequency. This pin is used as the master clock for
the servo motor circuits and may be used as a con 
venient test point.
Software contained in the U20 1 processor is uni 
que. It is used in single deck reproducers, three
deck reproducers and on the record logic board as
well. Support hardware for the processor on the
Record Logic board is significantly different than
that of the Play Logic board, but the software in the
microprocessor contains both the playback and re 
corder programs. For this reason, a single Delta
microprocessor chip may be used as a spare for
either record or play logic boards.
User selectable jumpers on the play logic board
enable the selection of several operational varia 
tions. Jumpers W202 and W203 select motor speed.
Units are shipped with speed set normal motor/tape
speed at 7.5 IPS. Jumper W202 selects 3.75 IPS, and
Jumper W203 selects 15 IPS. These will be discussed
in greater detail in the section for Motor and Servo
Amplifier. All Delta units utilize DC servo motors
which generate very little heat or electrical noise,
and are designed for continuous duty. Therefore, no
clear advantages are known in having the motor
run “ intermittent" duty, other than a very slight im 
provement of control room ambient mechanical
noise. Jumpers W206 and W207 select the flashing
READY lamp and repeat play lockout features.
Since the processor software is interchangeable
between Play and Record logic boards, a system
had to be devised whereby the processor “ knows"
which software to use. Pin 39, the T1 pin is used to
electrically signal the processor which software to
use. In reproducers, pin 39 is held “ low" by U204 pin
6. In recorders, this pin is held “ high" by a pullup to
+5 volts. The processor uses this pin to recognize
which software sections to use.
D. RECORD LOGIC
The Record Logic PCB is located in the Delta IV
Record Amplifier chassis, and executes and moni 
tors all recording functions. Although it functions
separately from the play processor and logic cir 
cuits, data transfer between it and the play proces 
sor is required for orderly machine functions. Serial
data is transferred into the Record processor via pin
12 from the reproducer, and out on pin 27. This
allows a logical "handshake" between the two pro 
cessors as they attend to their respective duties. The
data they exchange is serial, digital logic level, and
in a unique "language." Data exchange is ongoing
during the various machine functions. Due to com 
plexity it will not be discussed in detail.
Logical inputs from the front panel and remote
connector are inputted on pins 3 through 14 of
U1210. As in the Play Logic, all digital circuits are
"Active Low." Since the processor uses software pro 
grams common to the Play Logic processor, pin 39
of U1201 is pulled up to +V CC to identify to the pro 
cessor that it is being used on a Record Logic board.
See the discussion regarding this in the Play Logic
section. Other specific functions of the Record logic
will be detailed according to major circuit function.
Power-up reset is performed by U2 17 on the Play
Logic Board. Pin 4 of U1201 will be held low for a
short period of time after power-up until U217 tog 
gles. The “ low" condition on pin 4 of U 1201 causes
the processor to reset itself to a programmed start 
ing point, and causes all outputs to be set to a
predetermined state.
Processor clock functions are similar to those
discussed for the play processor with the exception
that a crystal frequency of 3.579 MHz is used.
The processor ALE line, pin 11 of U 1201, outputs
a pulse train that is l/15th the master clock fre 
quency. The ALE frequency, 238.6 kHz, is variously
divided by U1203, U1204, and U1205, then gated
by U1206A. U1206B, U1206C, and U1206D to output
a pulse train to the bias and cue generator circuits.
Bias Generation
The ALE frequency is fed into U1204 pin 1, di 
vided by two. and output via pin 3, U1204 to the bias
gate U1206A. pin 1. When the processor calls for
bias, U1206A pin 2 is pulled low, and enables the
output U1206A pin 3 to provide 119.3 kHz square
waves to QI 201. Simultaneously, processor U1201
pin 22 goes low, enabling the bias ramp circuit
U 1 208B. The result is a fast ramp "on" of bias occur 
ring at the board edge connector pin 8. This square
wave signal (119.3 kHz) is routed to the bias card for
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