Matsui 1410R, Service Manual

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3.2- Sound amplifier (IC7187)
Sound amplifier can be TDA7052 for 14" and 17" models or TDA7056 for 20" and 21" models.
Amplified sound is drived to the headphones output and loudspeakers. If headphones are connected, loudspeakers
are switched off.
Volume control on DC level is present at pin 4 for TDA7052 or pin 5 for TDA7056.
4.- POWER SUPPLY (Diagram D)
Mains isolated switched mode power supply (SMPS), controlled by IC7514 (TDA4605) in variable frequency
mode.
- Switching behaviour: The switching period is divided in on-time, when energy is extracted from the
mains into the primary winding (8-12 of 5525), off-time, when energy in the transformer is supplied to the
loads via secondary windings of 5525 and dead when no energy is extracted or supplied.
- Standby mode: Output voltages are present when the set is on stand by, due to standby is done cutting
line deflection. On-time is lower and power consumption is very low.
4.1- Primary side
- Degaussing: R3501 is a dual PTC (2 PTC’s in one housing). After switch on set, PTC is cold so low-
ohmic and so degaussing current is very high. After degaussing, PTC is heated so high-ohmic, so in
normal operation degaussing current is very low.
- Rectifier: Mains voltage is filtered by L5500, full wave rectified by diodes D6502-D6503-D6504-D6505
and smoothed by C2505 (300V. DC for 220V AC mains).
4.2- Control circuit (IC7514)
- Start up and supply (pin 6): When the set is switched on, a current via R3507 is applied to pin 6. When
C2514 is charged to 15V. the power supply starts and a current from pin 5 to T7525 is drived. T7525 and
starts conduction and a voltage across transformer windings is built up. The voltage across winding 4-2 is
rectified by diode D6521 and used to supply the IC on pin 6.
- Soft start (pin 7): The capacitor C2523 causes a slow increase of the duration of the output pulse during
start up.
- IC output (pin 5): This output drives T7525. R3523 is a fuse resistor to protect IC from short circuits in
T7525. D6516 limits the maximum voltage in T7525.
- Start conduction of T7525 (pin 8): A voltage proceeding from winding 4-2 is applied to this pin. The zero
crossing detector recognizes the complete discharge of the energy stored in the transformer core, in addition
to a dead time depending on C2508. This circuit guarantee that T7525 starts conduction at minimum Vds
voltage (see signals 4.5 pag 13).
- Primary current info (pin 2): Current primary winding is simulated by a pin 2 voltage.
- Output voltage info (pin 1): The voltage across winding 4-2 is rectified by diode D6515, divided by
R3527, R3518 and R3508 and applied to pin 1. Internal control voltage (Vcont) inversely proportional to V
pin 1 is generated. Tipical Vpin1 is 400 mV.
- Output regulation (pins 1, 2, 8): IC7514 stabilizes output voltage by controlling T-on and so the frequency
and the duty cycle:
Start pulse to T7525 is determined by pin 8 circuit (see signals 4.5 page 13 ).
Then a sawtood voltage Vpin 2 is generated at pin 2. Stop pulse to T7525 is produced when Vpin 2
reaches Vcont.
Output control is done by the following way:
If output is higher, Vpin 1 is higher, Vcont is lower, T-on and output will be reduced.
If output is lower, output will be increased.
Output voltage of supply can be adjusted by R3518.
Mains voltage variation is stabilized in the following way:
If mains voltage is higher, slope in the sawtood voltage Vpin 2 is higher, stop point is reached before
and T-on is reduced.
If mains voltage is lower, T-on is increased.