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| HORIZONTAL DEFLECTION SCHEMATIC. |
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19 |
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| 2SC5690 |
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| 100Ω |
| Horizontal | 2 |
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| NO DVM Hs |
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| Fil. |
| TC11 |
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| .9KVpp 27,G6 |
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20 | I11 |
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| Drive |
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| 1N4007 |
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| Fil. Rtn. |
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2.2nF | Transformer | 3 |
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| 435 |
| 433 |
| Video | Screen |
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| 1 | 4 |
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| 343 |
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| 1.2Ω |
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| Board | FOCUS |
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| 332 | 434 | GND |
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| 800 | EHT |
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| To Yoke |
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| FLYBACK |
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| HORIZONTAL | LA7851 | 415 |
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| 10 | TRANSFORMER |
| EHT | 092 | |||||||||
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| OSCILLATOR DISCHARGE | H. V+ |
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| 092A | ||||||||
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| 1K | ||||
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7 |
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| 10, E6 | 451 |
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| 465 |
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| Hs |
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| FOCUS |
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.2Vpp 07,E6 | 3.6Vpp 08,E6 | 7Vpp | 09,E6 |
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| 14 | 1K | 15 | H.Fo ADJ. |
| 170Ω | 336 | 452 | 8 |
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| SCREEN |
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13 | 33K |
| 17 |
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| Beam |
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| 680Ω | 340Ω |
| I14 |
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| I8 |
| I9 |
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| 7 |
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| 4 Current |
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| 9.31K | I15 | +200Hz |
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.01uF |
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| I16 |
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| 16 |
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| 3 |
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345 |
| I10 | +800Hz +400Hz |
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| To P/S |
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346 |
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| 2 | FIL. |
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| G | F |
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| V- |
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| 0Ω | ||||||
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| 453 |
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| 467 | |||||
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| GND |
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The voltage on capacitor 346 controls the
horizontal oscillator frequency via I8 . In the case
of missing horizontal sync pulses, the multiplier does
not sink current and flywheel capacitor | 344 |
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the horizontal frequency constant. Resistor |
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| I7 | |||
permits small rapid changes of the control voltage at pin 7 for locking of the oscillator to horizontal sync.
The horizontal oscillator capacitor 345 charges to its upper voltage limit through resistors
I10 , I16 , I15 , I14 , and 336 . This capacitor is
then discharged to the lower voltage limit through the action of discharge pin 9 and resistor I9 . The free running frequency (Hfo) may be adjusted by making solder connections on the I PRA. (see page 65 for the I PRA layout). In some cases where there are many missing horizontal sync pulses, it is necessary to adjust the Hfo closer than ±200 Hz. For fine tuning the Hfo, resistor 336 is replaced with a pot.
The horizontal phase locked loop then consists of an oscillator which sets the flyback timing.
The flyback pulse is then compared to the incoming sync pulse and the difference voltage holds the oscillator at the sync frequency.
The duty cycle of the horizontal drive transistor is generated by comparing the oscillator waveform against a fixed voltage. This fixed voltage is set by resistors 417 and 418 .
The horizontal output transistor 433 conducts about three amps of horizontal flyback transformer primary current and deflection yoke current. This transistor has a beta as low as three. To supply the high base current, a horizontal output transistor drive transformer is
used. The drive transformer | 332 |
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energy during the on time of | the | drive | |||||
transistor, |
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337 | |||||||
horizontal output | transistor |
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433 | |||||||
343and resistor I11 damps the drive transformer primary waveform. To reduce power dissipated by the horizontal output transistor during turnoff, a clamp circuit is connected to the drive transformer primary. This clamp consists of resistor 341 , capacitor
338, and diode 342 .
The flyback transformer's main function is to supply EHT to the CRT. It also supplies the focus and screen grid voltages which are taps on the EHT supply. There are three low voltage secondaries. One supplies the filament current, negative G1 voltage, and timing on the video board. Another supplies sync and EHT information to the power supply. The third secondary drives the horizontal blanking circuit and supplies sync for the horizontal PLL, the horizontal width control, & the vertical sync synchronizing circuits.
83
