9
Circuit description new circuits
36
L7.3A
•
X-ray protection. If the EHT will become too high, the tube
will radiate too much X-ray, this is detected by monitoring
the flyback pulses at pin 11 of the LOT.
•
Beam current protection. If the beamcurrent becomes too
high the Bimos is able to reduces this by making the
EHT_info line low. The circuitry around transistor 7481 in
circuit diagram A2, will detect this and create a PROT
signal.
•
The E/W amplifier has two protections. One protection for
overcurrent, for exampleshort circuit of E/W FET and one
protection for overvoltage; like interrupted capacitor in
lower half of the diode modulator.
Start-up of the horizontal oscillator via the (8V gives a start-up
current to pin 37; if the voltage on pin 37 exceeds 5V6 the
horizontal oscillator starts to oscillates at approx. 25kHz. Only
if the supply pin of IC 7225 (= pin 12 at IC 7225-5A in diagram
A4) becomes 8V the line frequency will change to 15625 Hz.
The horizontal synchronization separator separates horizontal
pulses out of CVBS signals and synchronizes the free-running
horizontal sawtooth generator. The horizontal oscillator
sawtooth is converted into a square wave voltage with variable
duty cycle. This square wave at pin 40 is fed to the line output
stage. The time constant of the synchronization circuit is
automatically internally determined by IC 7225-5D. Pin 41 is
SANDCASTLE output and also HORIZONTAL FLYBACK
input.
•
The SANDCASTLE has an output current a some mA, the
amplitudes of sandcastle pulse is : burst 5V3, line blanking
3V and during frame blanking 2V.
•
If the input acts as a HORIZONTAL FLYBACK pulse, the
input has a current of 100-300 mA. This horizontal flyback
pulse compares the phase of flyback pulse with phase of
the horizontal oscillator; if the phase is not correct the duty
cycle of horizontal oscillator will be adjusted.
•
Flash protection: The BCI info is applied to pin 42 of
IC7225-5D. If due to a flash in the picture tube the voltage
at pin 42 is > 6V, the horizontal drive will be switched off
immediately. If the voltage is again < 6V the horizontal
drive will be switched on again via the slow start procedure.
•
EHT over voltage protection. The BCI info is also applied to
pin 50 of IC7225-5D. First the BCI will compensate vertical
picture amplitude variations due to beam current
variations. The control range is between 1.2V and 2.8V.
However if the voltage at pin 50 exceeds 3.9V the EHT
overvoltage protection will be activated and the horizontal
drive is switched off.
The line output circuitry
In principle the line output stage pin 40 of IC 7225-5D drives
the line output stage consisting of TS 7445 and transformer
5445 via drivers TS 7440-7441. The line output stage supplies
the deflection current and the following supply voltages (see
also the power supply block diagram ) :
Output voltage (See diagram A2) LOT (5445 Line output
transformer) output voltage
•
EHT, + 200V, Vg2, focus and ff for the picture tube.
•
200V for the CRT drive
•
+ 5V for the control and tuner supply
•
+ 9V for the tuner supply
•
+ 11V for the control and vertical drive output
•
- 11V for the vertical drive output
Vertical synchronization IC 7225-5D and the frame
amplifier IC 7401
The vertical oscillator (= 50Hz) is controlled by the incoming
video signal. The vertical output is driven in anti-phase via the
pins 46 and 47. At pin 41 the so called "Sandcastle " pulse is
present; the sandcastle pulse is applied to several parts of the
circuits for timing purposes.
Frame amplifier
In principal the frame output stage IC 7401 (TDA9302H) is
used for the vertical deflection. This IC is controlled at pins 1
and 3 by the vertical control signal of IC 7225-5D and a
deflection current is generated at pin 5. The vertical flyback
signal is generated at pin 3 of this IC.
Protection of IC 7401; depending on +11V and -11V supply to
drive the vertical deflection CRT. In case of supply voltage
+11V or -11V needs a too high current, the VFL pin 3 of IC
7401 voltage will drop < 6.5V. As a result the VFL will feedback
this to pin 37 of 7600 micro processor and this will switch the
supply to stand-by mode.
9.6.5
Sound detector (IC7225-5E, diagram A4)
Single FM-mono sound for demodulation will take place in
IC7225-5E. No adjustment are required because of automatic
PLL tuning from 4.2 to 6.8 MHz .
9.7
Information of NVRam, tuners, video and audio
I.C.'s.
The following components are also applied in this chassis:
•
IC7620 in circuit diagram A5: NVRAM : ST24W04B1 (Non-
Volatile Memory). The ST24W04B1 is a 4k bit EEPROM
device. The enable pins E1 and E2 selects between
maximal four different ST24W04B ICs. Last status of a set
is stored in the EEPROM and can be retrieved whenever
there is a power interruption
•
Tuner 1000 in circuit diagram A4: UV1355 or UV1336 is
applied :
The list of tuners is as follows:
For 25” and 29” AP, tuner type UV1335 is used; Type of
tuning is VST.
For 25” and 29” Latam, tuner type UV1336 is used; Type of
tuning is PLL.
•
Audio IC's:
–
IC7310: TDA9860, Audio processor IC
–
IC7315: TDA9850, BTSC DBX decoder with SAP
–
IC7312: AN 7312, AVC= automatic Volume Correction
–
IC7202: MSP3410D, Nicam stereo decoder
–
IC7202: MSP3400C, 2CS Korea and 2CS German
decoder
–
IC7313: HEF4052, switch function IC
–
IC7311: TDA7057A , 2X3W stereo sound amplifier
For European and A/P sets we can have 2CS, mono/stereo/
dual sound: this is decoded by IC7202(=MSP3400/MSP3410)
on Nicam sound panel "C". Also Nicam mono/stereo/dual
sound is decoded by IC7202.
For A/P, Latam and USA we use the BTSC decoding ; see
IC7315 in circuit diagram A8.
NTSC/SECAM sound system IC (BTSC decoding IC)
General description of BTSC specifications
The BTSC sound system is based on the AM-FM method and
is capable of broadcasting:
–
MONO information {only MONO Carrier modulated}
–
STEREO information {MONO C -> 1/2(L+R) and STEREO
SC -> 1/2(L-R)}
–
DUAL information {MONO C -> language A and SAP SC -
> language B}
