Tektronix 3 - Page 9

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~ 5
No. 3 Electric Shutter
SECTION 5
OPTICAL AND ELECTRICAL DESCRIPTION
Circuit Description
Line voltage is supplied to the Speedcomputer via ON-OFF
switch SW1 (see electrical diagram), fuse Fl and transformer
Tl. Tl secondary has two voltage outputs; the approximate
27-volt output which is rectified and filtered by D7 and C7.
This supplies power to the actuate circuit. The approximate
160 volt output rectified and filtered by D2 and C2 supplies
power to the timing circuit, POWER indicator and the SHUT-
TER indicator via pins D and E of J10. The approximate 160
volt output is also rectified and filtered by D1] and Cl to
supply power to the shutter solenoid energizing.
Initially, when the Speedcomputer is turned on, a positive
voltage from the +160-volt supply is applied via R14, R17,
and R27 to the gate of silicon controlled rectifier (SCR) D25,
turning it on. SCR D15 is receiving anode voltage via shutter
solenoid K50, but it not conducting since the only way its
gate can get a positive signal is through ACTUATE switch
SW14 or the remote actuate circuit.
Operation of Bulb (B) Exposure-time Setting
The solenoid energizing circuitry for bulb (B) is the same
as was described above for an exposure-time speed setting
except, that as long as the actuating circuit is supplied with
+27 volts, transistor Q29 will be conducting. Q29 conduct-
ing will hold the voltage at the junction of R13 and D30 very
close to ground thereby not allowing C21 to charge up suf-
ficiently to fire B21.
The solenoid de-energizing circuit is the same as was
described for exposure-time speed settings since, once the
+27 volts to the actuating circuit is removed from Q29 it
will turn off and C21 will charge toward +160 volts using
R13 as the timing resistor.
Operation of All Exposure-time Settings Except
Time (T) and Bulb (B)
Actuating the circuit by either—(1) Pressing the ACTUATE
button, (2) shorting pins A and C of Remote Actuate con-
nector together, or (3) applying +27 VDC to pin A (use pin
B for ground) of the Remote Actuate connector, causes a
positive 27 volt initiating pulse to be applied to the gate
of silicon controlled rectifier (SCR) D15 via R12-C12, D12 and
R15, turning D15 on. At the same time D15 gate is receiving
a positive pulse, a pulse is also being sent toward the gate
of D25 via R22-C22, and D22. This positive pulse, however,
is shorted to ground via D21 and conducting SCR D25.
When D15 turns on, its anode voltage drops to a level
near ground, creating a negative voltage drop. This negative
voltage step is coupled through C17 to the anode of D25 and
through D17 and R27 to the gate of D25 causing D25 to turn
off. The negative voltage step is also applied to C21 via
D21, giving C21 a negative charge.
With D15 conducting, a current path is completed from
ground through D15, D10, shutter solenoid K50, R1, D1 and Tl
back to ground. Energizing K50, causes the contacts of K50A
to close and turn on the SHUTTER indicator B7.
Solenoid K50 remains energized until the charge across
C21 (which can now charge toward 160 volts through R29
and the selected timing resistor) becomes large enough to
fire neon lamp B21. The charge rate of C21 is controlled by
timing resistors selected by SW30. Zener diode D38 limits
the maximum charge across C21.
When B21 fires a positive pulse is coupled via R25 to
the gate of D25, turning it on. When D25 turns on, its anode
voltage drops to a level near ground, creating a negative
voltage step. This negative voltage step is coupled through
Cl17 to the anode of DI5 and through DI] and R15 to the
gate of D15, causing D15 to turn off.
With D15 not conducting the current path for K50 is broken
and the solenoid can not remain energized. As K50 de-
energizes it causes the contacts of K50A to open and the
SHUTTER indicator B7 extinguishes.
Operation of Time (T) Exposure-time Setting
The solenoid energizing circuitry for time (T) is the same
as was described above for an exposure-time speed setting,
therefore only the solenoid de-energizing circuit will be de-
scribed,
After the desired shutter open time, the actuating circuit
is again triggered (C21 cannot be charged to a plus voltage
because R40 returns ‘it to ground, therefore B21] can not
fire) by one of the three methods already described, causing
a +27 volt initiating pulse to be applied via R22-C22, D22 and
R25 to the gate of SCR D25, turning D25 on, At the same
time D25 gate is receiving a positive pulse, a pulse is also
being sent toward the gate of D15 via R12-C12 and D12. This
positive pulse, however, is routed to ground via D1] and con-
ducting SCR D15.
When D25 turns on, its anode voltage drops to a level
near ground, creating a negative voltage step. This negative
voltage step is coupled through C17 to the anode of D15 and
through D11 and R15 to the gate of D15, causing D15 to turn
off.
With D15 not conducting, the current path for K50 is
broken and the solenoid can not remain energized. As K50
de-energizes, it causes the contacts of K50A to open and the
SHUTTER indicator B7 extinguishes.
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