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Circuit Descriptions and Abbreviation List

GB 105

EM3E

Beam-current Correction

The ‘EHT-info’ signal at point 10 of the LOT, depends on the
value of the beam-current and the voltage from divider
R3450, R3451 and C2450. This signal is fed to the HOP to
trim the contrast, and to compensate for the changes in
picture-width as a function of the EHT-info, when EHT is
decreased. The ‘EHT-info’ is also used to correct the EW-
current.

The ‘DYN-FASE-CORR’ signal, derived from the ‘EHT-info’
signal, is fed to the HOP via C2455 and drives a dynamic
phase correction necessary because of beam-current
variations. This is done by regulating T

of the line transistor

TS7421.

9.10.4 Secondary Line Voltages

During the blocking time of TS7421, the magnetic energy of
coil 1 - 5 of the LOT, is transferred to electrical energy in the
secondary winding. Via rectifying and smoothing, the several
secondary supply voltages are generated, like:
•

EHT, Focus and Vg2-voltage

•

+200V for the CRT panel (pin 8 LOT)

•

+11D for the line deflection (pin 12 LOT)

•

+13VLOT for the frame deflection (pin 6 LOT)

•

-15VLOT for the frame deflection (pin 3 LOT)

•

Filament voltage (pin 9 LOT)

9.11 Vertical (Frame) Deflection (diagram A4)

9.11.1 Frame Stage Drive

Figure 9-12

The HOP drives the frame output stage with a symmetrical
saw-tooth voltage. As the HOP is 'cold' and the frame output
stage is 'hot', they are galvanic isolated. This is done via a
transformer (5621). As in the MG-chassis, the HOP
generates 3 signals needed for the frame output stage:
FRA, FRAMEDRIVE- and TILT (for rotation).
The rotation circuit is kept at the ‘cold’ side of the chassis, to
avoid the costs an extra optocoupler.
The circuit around IC7440 will amplify this signal and the
output current will flow through the rotation coil.

9.11.2 Flyback Generator

The frame output stage is supplied via the +13 V and -15 V
coming from the LOT. The output of the amplifier is 0 V

, so

a coupling capacitor is not required.

During the (forward) scan, a supply of +13 and -15 V is
sufficient to respond to the slow changing current. The
internal flyback generator puts a voltage of -15 V on pin 3.
Because of the voltage drop over zener diode D6622 (8.2 V),
C2622 will be charged to 19 V: being 13 + (15 - 8.2 - 0.7) V.
During the flyback scan, the change in current-per-time is
much larger, so a higher voltage is required. The flyback
generator will now generate a voltage of +13 V on pin 3.
Added to the charge on C2622 this will give a flyback voltage
of 32 V (depending on the CRT size, this value can differ).

The amplifier IC (IC7620, pin 5) supplies the saw-tooth
current to the frame deflection coil. The current through this
coil is measured via R3620//R3621//R3622 and fed back to
the inverting input of the amplifier.
R3624 and C2624 on the output of the amplifier, form a filter
for high frequencies and in that way also prevents
oscillations.
Peak voltages on the output, e.g. as a result of a possible
flash, are damped by the clamp circuit consisting of D6619,
C2627 and R3627. The network consisting of R3625, R3626,
R3629 and C2629 form an extra damping circuit.

9.11.3 Protection circuits

Bridge Coil Protection

The secondary voltage of the bridge coil L5422, is guarded at
the diode modulator (D6421/6422) via a 10 V zener diode
(6499 on diagram A3). When the bridge-coil is working
properly, the average voltage on D6422 is such that this
zener diode will conduct. It will drive TS7652 into saturation.
When, for any reason, the secondary side of the bridge coil
is shorted, the average voltage on D6422 will drop below the
zener-voltage, and TS7652 will block. Now capacitor C2642
is charged. Transistor TS7407 starts conducting and the
SUP-ENABLE signal is grounded via R3403. This will switch
‘off’ the main supply (see diagram A1).

CL 16532044_021.eps

140501

HOT

COLD

3407

3631

3640

FRAME
DEFL.
COIL

1620

ROTATION COIL

+8V

7440-A