HP mx703 Service Manual page 13

3-3-1 Horizontal Section
1. The oscillator is driven by the currents in R419 and R420. The minimum oscillator frequency is determined
by R419 and the maximum frequency is determined by R420.
2. Horizontal sync goes into pin 15 through R318. And horizontal flyback pulse goes into pin 1 through R401
from pin 5 of FBT for HFLB loop.
3. Horizontal driver (pin8) O/P to Q401 via C410.
3-3-2 Vertical Section
1. Vertical sync goes into pin 14 through R317.
2. The free running frequency is determined by R301 and C301.
3-3-3 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 TDA4863 AJ.
2. The TDA4863 AJ 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. This IC is powered by two sets of positive voltage and one set of negative voltage. (+12V at pin 1, -12V
at pin 4).
3-3-4 E-W/Trapezoid and H. Width Controls
1. The horizontal O/P stage uses diode modulator D419, C411, C412, L409 and C418 for East-West
(Pincushion) Trapezoid and H. width controls.
2. The scan current is determined by B
accomplished by OPAMP(KA324) I402 and Q419 by coupling a parabola waveform from pin 11 of
TDA4841. The H. width / corner and trapezoid correction are also accomplished by this pin 11. The DC
level controls H. size. The AC level is combined with side pin and trapezoid corners functions.
3-3-5 X-Ray Protection
1. To avoid X-ray hazard, a DC voltage generated at pin 5 of FBT and rectified by D410, C424 and divided
by R404, R406 and R405 come into pin 2 of TDA4841.
2. If this voltage is higher than 6.39 V, then TDA4841 will be activated to float HUNLOCK (pin17), H.
DRV( pin 8), B DRV (pin 6), VOUT1 (pin 12), VOUT2 (pin13). After that all deflection circuit stop
working.
3-3-6 G1, Blanking and Brightness
1. The vertical blanking signal comes from unlock pin 17 of I401. This positive vertical pulses through Q405
amplified and converted into negative pulse and sent to G1 for vertical blanking.
2. In protection mode or an out-of- range situation HUNLock will send 5 V pulse to CPU pin 30 of I701,
then G1 will go down to -150V. During the mode change, Mute acts as same as HUNLock's.
3-3-7 Contrast Section
1. Contrast is controlled by I701 through I
2. Beam current is detected through T402 (FBT) pin 7, C429, R449 and detected voltage feeding into pin 12
of I403 (KA324), R459, R548, C556 to control I501 pin 22 voltage. When I501 pin 22 voltage drops
+
minus Vm ( the voltage of C418) values and the pincushion control is
2
C bus to I501 (LM1247) directly.
HP mx703/m703
Page 11