SONY SEG1
Service Manual

levels of A- and B-channel cameras are very different, the camera lens f-stop should be readjusted. VIDEO INVERTER To produce a negative picture, an inverting one-stage amplifier, Q2, is employed in channel B. Gain and level adjustments are accomplished by VR2 and VR3 respectively. Either a negative or a positive picture can be obtained on channel B by means of SW-3. DISSOLVE The two selected signals are independently attenuated by dissolve potentiometers VR4 and VR5, mixed by R24 and R25 and, with SW5-a in the FADE position, presented to the video amplifier. WIPES When mode switch SW5-a is set to WIPE, analog gates Q3 and Q4 switch rapidly between the two selected channels in accordance with the logic signals on their bases. The switched video signals are mixed by R27 and R28. Logic signals are arranged so that whenever one transistor is turned on (turning off its video signal), the other is turned off. This guarantees that one channel or the other feeds the monitor at all times. WIPE LOGIC The logic signals that control these transistors are derived from the horizontal and vertical sync pulses. Each horizontal pulse triggers a one-shot multivibrator (Q21/Q22) whose 0� time is determined by the setting of the horizontal wipe pot VR6. At one extreme, a transition between channels is produced at the left side of the screen. At the other pot extreme, a long (60~µs) pulse is produced that delays the transition until the right side of the screen. Vertical wipe pot VR7 does a similar job at a slower (O-16 ms. ) rate: Vertical one-shot Q23/Q24, produces variable width pulses, triggered by the vertical pulse, for horizontal direction wipes. By using in combination independently adjustable pots VR6 (horizontal wipe) and VR7 (vertical wipe) and wipe selector switch, SW-6, it is possible to obtain four corner wipes, as well as vertical and horizontal wipes. The variable-duration pulses produced

by the two wipe one-shots are manipulated by resistor-transistor-logic (RTL) inverters IC-1, RTL NOR gate IC-2 and switches SW-6 to arrange the vertical, horizontal and corner wipes. CLAMPING The video signal selected by mode switch SW-5 is clamped to ground during blanking time by Q5. The horizontal blanking pulse includes front and back porch, while the vertical blanking pulse has only a back porch. The horizontal blanking pulse is developed from Camera #l and is a composite video signal. Sync separator Q8 produces mixed sync, which is a positive going 6 volt pulse. By means of a one-shot multivibrator (Q 9 /Q10), a 60-µs delayed pulse occurs about 2 µs in front of the sync pulse to form the front porch. The sync pulses are delayed by Cl6 to form the horizontal back porch. The horizontal front porch, mixed sync, horizontal back porch and the vertical blanking pulse are added with diodes Dl -D3 to give mixed blanking. This signal is sent to clamping transistor, Q5. VIDEO AMPLIFIER A two-stage feedback amplifier (Q6/Q7) is employed as the final stage. This gives low output impedance to drive two 75-ohm lines. Mixed sync from Camera #l is inserted at the output of the video amplifier. CAMERA DRIVE Two modes of camera drive, external and internal, are available. In the SEG-1, a two-toone interlace sync generator is installed which is phase locked to either incoming vertical pulses (through a Hirschmann male receptacle) or to internal 60 Hz line frequency. After the sync generator, both the horizontal and the vertical pulses are shaped by Q13 -Q16 and Ql7 -Q20 respectively. These pulse-shaping amplifiers can drive a 19 (75 + 4) ohm load with a 4-volt negative-going pulse. Due to the phase difference of horizontal driving pulses, a combination of DXC-Series and CVC-Series cameras is not recommended.