Daewoo CP-885, Service Manual

Page: 57 / 86

- 56 -
Service manual WP 895/895F, CP885/885F
5-7-2 Mode selection
The TDA894xJ has several functional modes, which can be selected by applying the proper DC voltage to pin MODE.
Mute : In this mode the amplifier is DC biased but not operational (no audio output). This allows the input coupling
capacitors to be charged to avoid pop-noise. The device is in mute mode when 2.5 V < V
MODE
< (Vcc-1.5 V).
Operating : In this mode the amplifier is operating normally. The operating mode is activated at V
MODE
< 0.5 V.
5-8 Vertical deflection
The vertical driver circuit is a bridge configuration. The deflection coil is connected between the output amplifiers,
which are driven in phase opposition. The differential input circuit is voltage driven. The input circuit is especially
intended for direct connection to driver circuits which deliver symmetrical current signals, but is also suitable for
asymmetrical currents. The output current of these devices is converted to voltages at the input pins via resistors R350
and R351. The differential input voltage is compared with the output current through the deflection coils measured as
voltage across R398, which provides internal feedback information. The voltage across R398 is proportional to the
output current.
5-8-1 Flyback voltage
The flyback voltage is determined by an additional supply voltage V
flb
. The principle of operation with two supply
voltages (class G) makes it possible to fix the supply voltage Vp optimum for the scan voltage and the second supply
voltage V
flb
optimum for the flyback voltage. Using this method, very high efficiency is achieved. The supply voltage
V
flb
is almost totally available as flyback voltage across the coil, this being possible due to the absence of a coupling
capacitor.
5-8-2 Protection
The output circuit has protection circuits for :
- Too high die temperature
- overvoltage of output stage A
5-8-3 Guard circuit
The guard signal is not used.
5-8-4 Damping resistor
For HF loop stability a damping resistor (R331) is connected across the deflection coil.
5-8-5 EAST-WEST Amplifier (TDA8358J)
The East-West amplifier is current driven. It can only sink currents of the diode modulator circuit. A feedback resistor
R397 is connected between the input and output of this inverting amplifier in order to convert the East-West correction
input into an output voltage.