Philips L9.2EAA, Руководство по обслуживанию

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Circuit description new circuits
GB 52 L9.2E 9.
the BIMOS is used as the feed back input from the CRT base
panel.
9.6.9 Beam current limiting
A beam current limiting circuit inside the BiMOS handles the
contrast and brightness control for the RGB signals. This
prevents the CRT tube being over driven, which may cause
serious damage in the line output stage. The reference used for
this purpose is the DC voltage on Pin 22 (BLCIN) of the TV-
processor. Contrast and brightness reduction of the RGB
output signals is therefore proportional to the voltage present
on this pin. Contrast reduction starts when the voltage on pin
22 is lower than 3.0 V. Brightness reduction starts when the
voltage on pin 22 is less than 2.0 V.
The voltage on pin 22 is normally 3.3V (limitor not active). To
enable correct operation however, an external adaptation to
the circuit is required for the correct functioning of the limiting
function. This is connected to Pin 22, the circuit therefore
ensures that correct peak white limiting and the average beam
current limiting takes place. Components 6212, 3246 are for
the average beam current limiting. As a reference for the
average beam current control the signal ABL_info is used. This
signal is a measurement of the picture contents. As the time
constant of the filter is much bigger than the frame period time,
the DC at the anode of 6212 represents the average value of
the picture content. Via 6212 and 2226 the DC voltage at pin
22 is slowly. The RGB output signals are applied to the CRT
panel via connector 0243. Via diodes 6213, 6214 and 6215 and
series resistor 3214, the RGB signals are also connected to the
CRT_discharge signal. The level of this signal is only high
during the time the set is switched off. And id due to the
cathodes of the CRT are driven fully negative. That means that
the beam current is increased. and consequently the CRT
quickly discharged.
9.6.10 CRT panel (see circuit diagram B)
On the CRT panel the analog output amplifiers for the RGB
signals are located.
The B-signal is amplified by the analog amplifier formed by a
circuit build around the transitors 7331, 7332 and 7333.
The G- signal is amplified by the analog amplifier formed by a
circuit build around the transitors 7321, 7322 and 7323. The
R- signal is amplified by the analog amplifier formed by a circuit
build around the transitors 7311, 7312 and 7313.
The supply voltage for the transistors is +160VA and is derived
from the line output stage.
9.7 List of abbreviations
2CS 2 Carrier Stereo
A/P Asia Pacific; schematic/PCB
information (only) applicable for Asia
Pacific sets
AFC Automatic Frequency Control
AQUADAG Aquadag coating on the (outside of
the) picture tube
AudioOutR Audio signal at Right output channel.
AudioOutL/Mono Audio signal at Left output channel /
Mono output channel.
AV_MUTE Signal to mute the sound on the Audio-
out of Cinch / Scart (Combined with
RBG_Blanking)
Ext2Fun_SW
(AV_Mute/
Ext2Fun_SW)
Switching signal from Scart2 to micro
controller indicating the presence and
type of signal on Scart2. (no signal /
CVBS 16:9 / CVBS 4:3)
AV Audio Video signal
AVL Automatic Volume Level
B_TXT_OSD Blue TXT or OSD signal from uC to the
video controller IC7250 (BIMOS)
BASS Control signal for BASS
BCI Beam Current information
BTSC Broadcast Television Standard
Committee; sound standard for
America and Asia Pacific
Buzzer Buzzer (only used in L9-ITV)
CRT DISCHARGE Fast drop of VBATT during after switch
off the set. Which result in EHT voltage
reducing to less than 18 kv within 5
sec.
CTI Colour Transient Improvement
CVBS Colour Video Blanking
Synchronisation. Video signal
containing colour, black/white,
blanking and synchronisation
information.
CVBS_EXT CVBS external = CVBS signal form
external source (VCR, DVD etc.)
CVBS_INT CVBS internal = CVBS signal from the
tuner
CVBS_MON CVBS monitor (CVBS) signal to Cinch
or Scart
CVBS_Terr CVBS Terrestrial output signal
CVBS_TXT CVBS for TXT processing in micro
controller
Din Digital input signal only used in L9-
ITV)
Dout Digital output signal (only used in L9-
ITV)
DBX Dynamic Bass Expander (only used
for BTSC sound system)
DNR Dynamic Noise Reduction
EAR Earth (ground layer)
EEPROM Electrically Erasable Programmable
Read Only Memory (also called NVM;
non-volatile memory)
EHT-INFO Extra high tension information; Beam
current related signal from CRT to
BIMOS.
Ext1 B RGB External 1 Blue input signal.
Ext1 FB RGB External 1 Fast-blanking input
signal.
Ext1 G RGB External 1 Green input signal.
Ext1 R RGB External 1 Red input signal.
Ext1 Video RGB External 1 Video input signal.
Ext2 AudioL/Mono External 2 Audio Left input signal /
Mono input signal.
Ext Audio/Mono External Audio input signal / Mono
input signal.
Ext2 AudioR External 2 Audio Right input signal.
Ext2C Exterial 2 SVHS Chrominance (C)
input signal.
Ext2Video/Y External 2 Video input signal or SVHS
Luminance (Y) input signal.
ESD Electrostatic Discharge
EURO Europe; schematic/PCB information
(only) applicable for European sets
EWD_dyn Dynamic East-West correction to
compensate for variations in EHT
EWDRIVE East-West drive correction
FB_TXT_OSD Fast blanking signal from micro
controller to IC7250 (BIMOS) for
inserting or displaying TXT and OSD
information (generated by the micro
processor)
Filament Filament (heater voltage) from LOT to
CRT
FBL Fast Blanking
FFBL Full screen Fast Blanking