Deflection Current Compensation Circuit - NEC FP1355 Service Manual

1.2.2

Deflection current compensation circuit

As the picture becomes flatter, the arrival distance of the deflected electronic beam becomes
more different between the center and both ends of the picture. Therefore, there is a tendency
for the image to be contracted at the center of the picture and expanded at both ends of the
picture. Moreover, the left side of the picture is more expanded than the right side of the pic-
ture owing to the characteristics of the circuit. CS applies S type compensation to the deflec-
tion current with the resonant effect of the deflection yoke and contracts at both ends of the
horizontal axis. The linearity coil increases the inductance of the starting section of the deflec-
tion current with the supersaturated reactor, and works to contract the left side of the horizon-
tal axis.
As the frequency is lower, the capacity of CS is generally increased and the linearity coil with a
larger impedance value is used. In the practical circuit, seven CS capacitors are prepared, and
are combined as desired. The linearity coil changes inductance by letting the control current
corresponding to the horizontal frequency flow to the control coil.
(1) S type compensation with CS
CS is switched in seven steps by FET. IC501 element with six FETs included and Q510 are
used. On IC501, pins 2, 5, 7, 9, 11 and 13 are used as the gate, and pins 3, 6, 8, 10, 12
and 14 are used as the drain. Pins 1 and 15 are used as the ground, and each source are
grounded to the earth. The binary value signal of HIGH (5V) or LOW (0V) is input to each
gate by IC102. In case of HIGH, FET is turned ON. In case of LOW, FET is turned OFF.
The correspondence to the signals from the capacitor and IC102 are as follows.
(2) Compensation with linearity coil
The linearity coil compensates the left expansion of raster by changing the inductance
value through the current value flow in order to keep the horizontal linearity to appropriate
level. In the actual circuit, L540 stands for the linearity coil.
The newly adopted linearity coil is provided with a control winding capable of controlling the current
characteristics of the inductance value. The control voltage (DC) corresponding to each horizontal
frequency is supplied from pin 2 of IC101 to pass the control current to the control winding through
IC103 and Q540. This controls the current characteristics of the inductance value, and eventually
keeps the horizontal linearity to appropriate level. An image of characteristic of linearity coil is as
fugure 11.
G D
FET1 2 3
FET2 5 6
FET3 7 8
FET4 9 10
FET5 11 12
FET6 13 14
FET7
(Q510)
The column of G and D is Pin No.
Table 3
Capacitor
C523
C524
C525
C526
C527
C528
C529
1 - 22
Signal
CS2
CS1
CS5
CS6
CS3
CS4
CS7