Tektronix 070-8462-03, Инструкция по эксплуатации

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Theory of Operation
4–10
1735 HD High Definition Waveform Monitor
Selection is accomplished by the readout enable (ROEN) from the microcontrol-
ler, through U23B. When the control line goes high, U23B (pin 7) goes low to
turn off Q11. When Q11 is off, U26B common-modes out the horizontal position
control voltage and U26B (pin 7) is at 0 V regardless of the front-panel position
control setting.
RGB or X Input Amplifier.
Q13 and Q12 form the input amplifier for RGB/ YRGB
staircase input to the Horizontal Output Amplifier. Input is through the rear-panel
REMOTE connector.
In non-RGB operation, the RGBEN control line is low, saturating Q7, Q13, and
Q12. The collector of Q13 is at 0 V and the RGB input is disabled.
To enable RGB, the control line is pulled high, un-saturating the amplifier and
allowing the output signal to be summed into the horizontal magnifier amplifier
summing point, instead of the ramp from the sweep generator. In addition, when
RGB is enabled, Q18 is turned on to shorten the horizontal sweep. A jumper at
J6 allows for selection of either 3-step staircase (for RGB) or 4-step staircase (for
YRGB). The input staircase is a negative-going signal of approximately 10 V
peak-to-peak. The offset control (R92) provides adjustment for the different
average DC levels from the cameras. C57 is the input compensation adjustment.
When external horizontal input is used to drive the horizontal axis, the sweep
generator is turned off by keeping Q16 on (/SWPGATE high). A negative
voltage applied to the rear-panel REMOTE connector (pin 2) deflects the
horizontal sweep from the left to the right at approximately 1 division per volt.
Horizontal Limit Amplifier.
The horizontal limit amplifier, which consists of
Q25A, Q25B and Q22, controls the gain of the sweep ramps. The input is a
summing junction at the base of Q25B, adding the output currents from the
sweep generator, HORIZONTAL position, and the RGB staircase input
amplifier. The output is the collector of Q22. Limiting occurs when the output is
driven above 9 V (Q22 saturates) or below ground (CR10 turns on).
Feedback through R154 and R204 can be selectively shunted by turning on
combinations of Q17, Q19, and Q20.
U20B is an adjustable voltage supply to provide the registration needed to
magnify the trace at the center of the CRT.
Off-screen Blanking. Comparators U29A and B sense the output of the horizontal
limit amplifier. If Q22 is saturated or cut off (which corresponds to the CRT
beam being off screen to the right or left), the output of either U29A or B goes
low and causes the CRT beam to be blanked. Q23 and Q21 form a fast pull-up to
unblank the CRT when the beam comes back into the screen area.