Philips Chassis EM1.1A AA, Руководство по обслуживанию

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Circuit Descriptions, Abbreviation List, and IC Data Sheets EN 105 EM1.1A AA 9.
It is important, that the Main supply is switched 'off' before the
Standby supply. This is in order to prevent several unwanted
phenomena, such as audible plops and visible switch off spots.
Without an extra circuit to force this, this cannot be achieved.
Therefore, the circuit around TS7505 and TS7508 (diagram
A1A) is implemented.
This circuit compares the Main DC voltage (+375 V) and a
reference voltage (V
BAT
) via resistors R3554, R3555, R3560,
and R3556. Elcap C2539 serves as voltage source for the two
transistors.
When the Main DC voltage will decrease w.r.t. the reference
voltage VBAT, the 'SUP_ENABLE' line will be activated via
TS7505, TS7508 and R3559. This will switch 'off' the Main
supply via TS7529.
Switch to 'On' (via 'SUP-ENABLE')
Via the 'STANDBY' command from the Painter, the MOSFETS
7141 and 7131 (diagram A2) are switched 'on.' When the
Painter senses the +5V and +8V, a command is given to the
HOP to start the drive (via I
2
C).
When this is sensed via the 'SUP-ENABLE' line (at the base of
line transistor TS7421, diagram A3), the main supply is
switched 'on' via TS7529 (diagram A1).
Protection
When, for any reason (interruptions or defective components),
the feedback loop of the Main supply fails, the V
BAT
will rise.
This is detected via zener diodes D6507, D6508, and D6513.
This will 'ignite' thyristor T7503, which will result in the blowing
of fuse 1503.
Audio Supply
The pulses on the secondary winding of L5506 (or L5512) are
rectified by D6535 (+16 V) and D6536 (-16V), and smoothed by
C2542 and C2543.
9.4
Control (Diagram B7)
9.4.1
Painter
Introduction
The SAA5667 (IC7001) is called the Painter. The
microprocessor and the TXT/OSD-decoder are integrated in
this IC. Some of its functions are:
•
Set control.
•
TXT/OSD acquisition.
•
RGB-outputs to the HOP
•
Menu blending; for blending the contrast, software
controlled.
•
I/O-ports for I
2
C, RC5, LED, and service modes.
•
Error code generation.
Data Storage
•
The set software is integrated in the Painter.
•
The Non Volatile Memory IC7001 is a 4 kB version
M24C32, and is used to store data of a working set.
Power Supply
The Painter is supplied with 3V3. For this voltage, a 3V3
stabilizer is used (IC7005).
With the circuitry around TS7003 and 7004 (diagram B7), a
reset is generated to wake up the Painter (pin 74). During this
reset, all I/O pins of the Painter are made 'high.'
9.4.2
TXT/OSD
The horizontal (H
D
) and vertical (V
SYNC
) sync pulses are also
fed to the Painter for stable OSD and TXT.
This IC gets its video signal directly (from the HIP) on pin 31.
The RGB-outputs (46/47/48) together with the fast blanking
signal (pin 52) are fed to the HOP.
9.4.3
I
2
C Bus
There are two I
2
C busses used:
•
Slow (max. 100 kHz) hardware I
2
C-bus (called SDA_S/
SCL_S), used for all ICs.
•
Separate short bus (called SDA_NVM/SCL_NVM) for the
Non Volatile Memory (NVM), to avoid data corruption.
Note: In the diagrams you can also find a bus called SDA_F/
SCL_F (F= fast), but in this chassis it is connected to the 'slow'
bus.
9.4.4
NVM
The Non Volatile Memory contains all set related data that must
be kept permanently, such as:
•
Software identification.
•
Operational hours.
•
Error codes.
•
Option codes.
•
All factory alignments.
•
Last Status items for the cu a complete factory
recall.
9.5
Tuner and IF (Diagram A8 and B2)
The tuner is I
2
C controlled, and is capable of receiving off-air
and cable channels.
Tuning is done via I
2
C. The reference voltage on pin 9 is 33 V.
This voltage (V
TUN
) is derived from the secondary side of the
standby supply, via D6110 and R3116//R3115 and a 33 V
zener diode (D6200). The Painter, together with the HIP,
controls the tuning procedure. There is also automatic
switching for the different video systems.
The IF-filter is integrated in a SAW (Surface Acoustic Wave)
filter. The type of this filter depends on the received
standard(s). There are two SAW filters: one for filtering picture-
IF and a second one for sound-IF.
The output of the tuner is controlled via an IF-amplifier with
AGC-control. This is a voltage feedback from pin 62 of the HIP
to pin 1 of the tuner. AGC take-over point is adjusted via the
service alignment mode 'Tuner - AGC.'
Service tip: If there is too much noise in the picture, it is
possible that the AGC setting is wrong. It is also possible that
the AGC setting is misaligned if the picture is deformed with a
perfect signal. Then the IF-circuit is amplifying too much.
The video IF-signal is fed to pins 2 and 3 of the PLL-controlled
IF-demodulator. The voltage-controlled oscillator of the PLL is
adjusted via the service menu 'IF PLL OFFSET.' If the
alignment is correct, the frequency displayed in the installation
menu is the same as the applied frequency from a generator.
The external coil L5408 connected between pins 7 and 8 is
used as reference.
The demodulated IF-video signal is available at pin 10 of the
HIP. In this video signal, there is a rest of the sound carrier,
which is filtered out by the sound trap 1407.
Via TS7322, the signal is supplied to AV1 (monitor out) and
again back into the HIP (pin 14) to the source/record selection.
To achieve Quasi Split Sound (QSS), the IF-signal is fed to the
HIP on pin 63/64 via SAW-filter 1405. The FM- modulated
signal is available on pin 5 and is fed to the audio demodulator
MSP34xx (7651, diagram B6).