Atec Tektronix-1502 - Manual (Page 29)

TM 9-4935-601-14-3&P
Bias current for tunnel diode CR1703 is provided by R1601 and R1693. Transistors Q1602 and Q1603
serve as a switch to direct the current through the tunnel diode via Q1603 or to divert the current to ground via
Q1602. TUNNEL DIODE RESET (U1671D output), which is high during time slots 1 and 4, is used to switch
between Q1602 and Q1603. When the base of Q1583 goes high, its output to Q1589 goes low. The emitter of
Q1589 goes low, turning Q1595 on, which turns Q1602 on (through Q1502) and Q1603 off (through Q1504).
CR1703 is then off.
Figure 3-3. Program Logic Cycle.
REV A FEB 1980
3-4