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Operation Theory
MD 1998LE (B1997PNST)
controllable by I
2
C bus. SDA and SCL signals coming from microprocessor feed to pin 19 and pin 18 to
control all functions.
3-3-1 Horizontal Section
1. The oscillator is driven by the currents in R424 and R423. The minimum oscillator frequency is determined
by R424 and the maximum frequency is determined by R423.
2. Horizontal sync goes into pin 15 through R314. And horizontal flyback pulse goes into pin 1 through C455,
C437, R404, C458, R40E and bypass filter C401 from Vcp of Q424 collector for AFC loop.
3-3-2 Horizontal O/P Section
1. Horizontal driver (pin8) signal is sent to Q402 via R496, C451.
2. Signal from Q427 direct drive T403, through R493 (shunt with R4A4, R40F, R40G) and L405 to horizontal
output transistor Q424.
3-3-3 Vertical Section
1. Vertical sync signal from micro controller is connected to pin 14 through R313.
2. The free running frequency is determined by R319 and C312.
3-3-4 Vertical O/P section
1. The differential output currents from pin 13 of Vout1 and pin 12 of Vout2 can be directly coupled to the
vertical deflection booster pin 1 and pin 2 of TDA8351.
2. The TDA8351 has two output stages which are current driven in opposite phase and operate in combination
with the deflection coil in a full bridge configuration.
3-3-5 E-W/Trapezoid and H. Size Controls
1. The B+ driver for step down circuit is from pin 6, it provides 20~80% duty cycle outputs according
to H-frequency.
2. The E/W / Trapezoid and H-size controls are through B+ modulation at I401 TDA4856. The EW output
signal is from pin 11, it’s not tracking with H-frequency.
3-3-6 X-Ray Protection
1. To avoid X-ray hazard, a DC voltage generated at pin 3 of FBT and rectified by D108, C121 is divided by
R126, R129 and C402 filter go into pin 2 of TDA4856.
2. If this voltage is higher than 6.39 V, then TDA4856 will be activated to float HUNLOCK (pin 17), H. DRV
( pin 8), B DRV (pin 6), VOUT1 (pin 12), VOUT2 (pin 13). After that all deflection circuit stop working.
3-3-7 G1, Blanking and Brightness
1. The vertical blanking signal comes in two ways. One is from pin 8 of I301 (TDA8351), the other is from
HUNLK (pin 17 of I401). These two positive vertical pulses through Q42A, Q42C, Q42E amplified and
converted into negative pulse and sent to G1 for vertical blanking.
