Tektronix 5441 Instruction Manual page 43

Theory of Operation-5441 /R5441
Collirnation Electrodes (CE)
The CE 1 and 2, and the CE 3 circuits consist of an
emitter follower, Q655 and Q600, with base-emitter reverse
voltage protection furnished by CR655 or CR600. R655,
CE 1 and R600, CE 3 adjustments control the voltage level
of the CE 1 and 2, and CE 3, respectively. CE 1 and 2 volt-
age varies between store and non-store modes of opera-
tion. R655, CE 1 adjustment, sets the CE 1 and 2 level in
the store mode, while R654 and VR655 sets the CE 1 and
CE 2 level in the non-store mode. I365543657 divider is al-
lowed to float in the non-store mode.
Collector Mesh
Emitter follower (2595, base-emitter reverse voltage pro-
tection diode CR595 and Zener diode VR595 make up the
collector mesh circuitry. VR595 sets the base voltage for
Q595.
Storage Mesh
(2580, Q575, and Q585 form an operational amplifier that
is used as a current-to-voltage conversion amplifier. Internal
adjustments R572, Prep Level, and R590, Op Level, set the
quiescent operating levels for the crt in the storage mode.
R585, WRITING SPEED control, allows a small adjustment
to be made in the operate level, which increases the crt's
ability to store a fast waveform. During the erase cycle the
storage mesh is made a high positive for 50 ms, returned to
its operate level for 10 rns, then made a slightly positive
level for 440 ms. The two positive-going erase signals (see
Fig. 3-1 ) are supplied to the storage mesh by the collectors
of Q515 (50 ms) and Q555 (440 rns).
Erase Generator
Pushing the ERASE pushbutton creates a negative pulse
at the base of (2510. R665-R500-C500 is a contact bounce
remover network for the ERASE pushbutton with R500
used to dampen any ringing. Q510 and Q515 form a 50 rns
monostable rnultivibrator; C514 and R501 are the timing
components. Coupling capacitor C528 couples the 50 ms
multivibrator to the input of the 10 ms monostable multi-
vibrator consisting of Q5304535. The timing components
for Q530-Q535 are C534 and R530. The output from the
10 rns multivibrator is coupled to the input of the 440 ms
monostable multivibrator by C538. (2550-Q555, along with
timing components C554 and R545 form the 440 ms
monostable multivibrator. The monostable multivibrators
are cascaded to provide a sequential pulse train. Diodes
CR560, CR562 and CR564 make up an OR gate to supply a
composite erase signal to the flood-gun anode circuit.
The signal available from the collector of Q550 is used to
retrigger the erase generator when the ERASE pushbutton
is held in.
Variable Persistence and Save
Q625 and Q640 form a monostable rnultivibrator that is
triggered by the output of the 10 ms pulse generator con-
sisting of programmable unijunction transistor (2610. The
timing components for the monostable rnultivibrator are
C625, R622, and R620, VARIABLE PERSIST control. The
10 rns pulse generator timing components are C610, R608,
and R609. Q635 acts as a switch for R620, VARIABLE
PERSIST control.
n
This level controlled by R 5 9 0
Signal from
This distance set by R572
Prep Level and is not affected by
0 5 1 5 c o l l e c t o d B
R590 Op Level adjustments
Signal from
0 5 3 5 collector
Signal from
0 5 5 5 collector
-'J=iG
L
-
-
440 rns
-
R585A WRITING SPEEDcontrol changes Op level, but
distance
prep
level is above 0 V remains constant.
Fig. 3-1. Erase cycle waveform as seen at the storage mesh-connection to the crt.
REV MAY 1982