Tektronix 070-8462-03, Instruction Manual

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Theory of Operation
4–22
1735 HD High Definition Waveform Monitor
Trace Rotate. Trace rotation is necessary to compensate for changes in the
magnetic field surrounding the 1735 HD. Q18 and Q19 are emitter followers that
provide the trace rotation current to a coil located inside the CRT shield, around
the tube. Current amplitude and polarity are controlled by the front-panel
ROTATE screwdriver adjustment.
Z-Axis Control. The outputs of four switchable current sources, combined in
parallel, drive the Z-axis amplifier (the base of Q3, shown on Diagram 15). If
there is no current going to the Z-axis amplifier, the CRT will be blanked (no
trace).
Current source U44A is described in detail below. U44B, U45A, and U45B
operate similarly.
Currents from R115 and R173 sum at U44A pin 3. If the switch control input at
U44A pin 1 is a logic low, the current source is ON, and the current is passed to
the Z-axis amplifier input via U44A pin 13. Otherwise the current source is OFF,
and the current is passed to the +5 V supply via U44A pin 14. The current source
is biased by R97, CR4, and CR5 so that the logic threshold at pin 1 is near 1.3 V,
and current input at pin 3 is near ground.
Display
Diagram <12>