Crossover Vertical Interface; Detailed Block Diagram Of Trigger Selector - Tektronix 7844 Instruction Manual

T R I G G E R S I GNAL
AMPLI F I E R
F R OM LEFT
VE RTICAL U N I T
o
R I GHT T R I G G E R
TR I G G E R SIGNAL
FROM R I G H T AMPL I F I E R
VE RTICAL UNIT
Trigger Selector circuit is shown on diagram 6 at the rear of
this manual.
Trigger Amplifier
The trigger amplifier stages (U41 5 and U51 5) receive trig·
ger signals from their respective vertical plug·in compart­
ments and supply trigger signals to both channel switches.
A and B Trigger Channel Switches
The A Trigger Channel Switch circuit routes trigger sig­
nals from either the LEFT VERT or RIGHT V ERT plug·in
compartments to the A HORIZ plug-in compartment. The A
TRIG SOU RCE switch (S1 6 1 ) determines which trigger sig­
nal will be allowed to pass through the A Trigger Channel
Switch circuit.
The A Trigger Channel Switch operates as follows: first,
assume that pin 1 of P445 is grounded by the A TRIG
SOURCE switch. Transistor 0556 saturates when its base
goes negative. The voltage at the emitter of 0556 also goes
negative and turns 0550 off. The collector of 0550 then
goes positive to reverse bias CR546. Transistors 0560 and
0558 are forward biased by the emitter voltage of 0556,
which provides the signal path for the trigger signals from
pins 6 and 8 of U51 5 to J552 and J451 . At the same time,
REV J U N 1 981
U415
Fig. 3·1 3. Detailed block diagram of Trigger Selector circuit.
Theory of Operation-7844/R7844 Service
FROM
B TR I G
SOURCE
B T R I G G E R
SW ITCH
0428, 0528
0430, 0530
A T R I G G E R
CHAN N E L
SWITCH
0450, 0550 t- - - -
0456, 0556
0458, 0558
0460, 0560
FROM
A T R I G
SOURCE
SWI TCH
0456 turns off to reverse bias 0460 and 0458, which pre·
vents the triggf3r signals from pins 6 and 8 of U41 5 from
reaching J552 and J451 . Also, 0450 turns on and forward
+
biases CR446, which shunts the trigger signal from pins 6
and 8 of U41 5 to the 5 V supply through 0450.
Conversely, when pin 1 of P445 is ungrounded, 0560
and 0558 are mverse biased preventing the trigger signal at
pins 6 and 8 of U51 5 from reaching J552 and J451 . At the
same time, 0458 and 0460 are forward biased providing a
path for the trigger signal from pins 6 and 8 of U41 5 to
reach J552 and J451 .
The B Trigger Channel Switch stage routes trigger sig­
nals from either the LEFT VERT or RIGHT VERT plug-in
compartment to the B HORIZ plug·in compartment. Other­
wise, the operation of the B Trigger Channel Switch is the
same as for the A Trigger Channel Switch.

Crossover Vertical Interface

The Crossover Vertical Interface stage determines
whether the Left or Right Vertical units provide the input
signal to the Beam 1 and Beam 2 Vertical Amplifiers as
selected by the V ERTICAL MODE switch (diagram 2). Sep­
arate preamplifif3rs are provided for the left and right vertical
TR IGG E R SIGNAL
o
UNIT
TRIGGER SIGNAL
TO A HORI ZONTAL
UNIT
1 6 76-86
0
3- 1 9