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To obtain a smooth switch-on and switch-off behaviour of the horizontal output stage the horizontal drive signal is switched-on and off via the soft-start/soft-stop procedure. This function is realised by means of a variation of the TON of the horizontal drive pulse. When the soft-start procedure is completed the horizontal output is gated with the flyback pulse so that the horizontal output transistor cannot be switched-on during the flyback time. Over voltage conditions (X-ray protection) can be detected via the EHT tracking pin. The horizontal drive output pin 40 of I501 has an external pull up resistor to the 8V supply R533. The output is applied to the base of Q701 via R707. The collector is supplied from the +B via R705 and the primary of the drive transformer T702. The secondary of T702 drives the base of the line output transistor Q751. The collector is supplied from the +B via R735, L700 and the primary of the flyback Transformer. The horizontal feed back to I501 pin 41 is taken from the collector of Q751 by capacitive divider C748/C769 & C708, passed through the R/C network of R724 & C724/C723 to the 5V6 Zener diode Z704, which is then clamped by diodes D713 & D714. It then passes through R765 to the base of Q711, the emitter of which as a pull up resistor to the 8V R769, this output is the applied to pin 41 I501 via R768. A sandcastle pulse is visible at pin 41 is internally generated by I501. Pin 50 (EHTO) I501 is used in 2 ways the first for EHT compensation, and is connected to the ACL pin 4 of T700 via R737 and R605. This is used to alter the frame amplitude when extremes of picture content are reached (bright or dark) to reduce the visible breathing. Secondly it is used by the microprocessor I003 pin 1 to turn off the horizontal drive at mains off, standby and under fault conditions. A high is output from pin 1 (shutdown), applied to the base of Q 605 via R667. Q605 turns on pulling the base of Q606 low, which turns on applying a high voltage to pin 50 I501 via R616 and D603.
The horizontal drive will be stopped when pin 50 I501 exceeds 3.9V
VERTICAL DEFLECTION
The vertical deflection output IC I601 (TDA8358J) is a differential current amplifier. I501 generates the vertical drive pluses; C518 the vertical sawtooth capacitor is connected to pin 51 (VCS). The drive pulses are output from I501 pins 46 (VDRB) and 47 (VDRA), to I601 pins 2 & 1 respectfully via R608 and R607. The supply voltage to pin 3 is generated by the FBT, is output from pin 5 rectified by D708 and smoothed by C726. The flyback pulse generator supply voltage also comes from the FBT, from pin 8 is rectified by D604 and smoothed by C616.
Pin 1 2 3 4 5 6 7 8 9 10 11 12 13
Description Vertical input (positive) Vertical input (negative) Supply voltage Vertical output voltage B East-West input voltage (not used) Vertical ground East-West ground East-West output voltage (not used) Flyback supply voltage Vertical output voltage A Guard output voltage (not used) Input measuring resistor Input compensation current
The East-West amplifier within the TDA8358 is not used in this application.
