Tektronix 2215, Instruction Manual

Page: 83 / 345

voltage at one end o f C644 at about 3 V , w hile the Q
o u tp u t o f U640B at pin 9 is H I. When the Q o u tp u t o f
U640B goes LO at the start o f the h o ld o ff period, C644
couples the negative-going edge o f the pulse to the A lt Sync
signal line.
Capacitor C644 charges ra p id ly to the new voltage
difference through R642 to produce a very narrow pulse
o u tp u t across R642. When the h o ld o ff period ends, the
Q o u tp u t o f U640B goes HI again and C644 charges in the
opposite direction through V R 644. The positive-going edge
o f the diffe re n tia te d h o ld o ff pulse is very small in
am plitude and does n o t affect the c irc u itry to w hich the
A lt Sync signal is applied.
The A lt Sync signal is fed to tw o places: the A lte rn a te
Sweep c irc u it and the Channel S w itching c irc u it. It is used
to synchronize the h orizontal display w ith channel
sw itching transitions when using A L T V E R T IC A L MODE
and to alternately switch between the A and B Sweeps
when using A L T H O R IZ O N T A L MODE.
ALTERNATE B SWEEP
The A lternate B Sweep c irc u itry , shown on Diagram 10,
produces the B sawtooth voltage th a t is am plified by the
H orizontal A m p lifie r to provide the B Sweep horizontal
d eflection on the crt. The A lternate B Sweep c irc u itry also
produces the sweep-switching signals, th a t c o n tro l the
display o f the A and B Sweeps, and the gate waveform s
used by the A u to Intensity and Z-A xis circu its to establish