Tektronix 434, Instruction Manual

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Circuit Description—434
s im ila r to th a t described fo r the Erase M u ltiv ib ra to r. When
e ith e r E N H A N C E s w itch (S90C o r S92C) is pushed in,
Q 1 2 4 5 has a c o n d u c tio n path to ground th ro u g h R 1245.
Q 1 2 4 5 saturates and the lo w voltage-level at th e c o lle c to r
o f Q 1 2 4 5 keeps Q 1246 tu rn e d o ff. T h e negative-going
p o rtio n o f th e Enhance T rig g e r pulse fro m the Sweep
c irc u it is co upled th ro u g h C l 24 0 to sw itch th e Enhance
M u ltiv ib ra to r. Q 1 2 4 5 tu rn s o f f and Q 1 2 4 6 tu rn s on. The
c o lle c to r o f Q 1 2 4 6 snaps d o w n to a b o u t —15 volts
p ro d u c in g a negative-going step w h ich is co u p led th ro u g h
C l 24 6 , and tu rn s o f f C R 1 2 4 5 . The length o f tim e th a t the
m u ltiv ib r a to r rem ains in th is state, and th u s the pulse
w id th , is d e te rm in e d by th e values o f R 1244 and C 1246.
T h e se ttin g o f th e E N H A N C E L E V E L c o n tro l, R 92, d e te r­
mines the a m p litu d e o f th e pulse w h ic h is a pplied to th e
feedback a m p lifie r sum m ing p o in t.
1 integrate
T h e second fast w ritin g te ch n iq u e to be discussed is
in te g ra tio n . In th is m ode o f o p e ra tio n , th e flo o d gun beam
is in te rru p te d m o m e n ta rily , a llo w in g th e w ritin g gun beam
to sum small a m o u n ts o f charge fo r successive sweeps so
th a t w hen the flo o d e lectrons are again tu rn e d o n , the
scanned ta rg e t area sh ifts to th e stored state. T h is is
accom plished b y pressing the IN T E G R A T E s w itc h , S94,
w h ic h disconnects the flo o d gun cathodes. T h is also
connects —75 vo lts to the e rro r signal in p u t te rm in a l o f the
high-voltage re g u la to r c ir c u it th ro u g h R 960 to s h ift the
high voltage s lig h tly , c o rre c tin g fo r th e d e fle c tio n sensi­
t iv it y changes th a t o ccu r w hen the flo o d guns are tu rn e d
o ff. Releasing the IN T E G R A T E s w itc h , th e n , allow s the
disp la y to s h ift to the stored state.
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