Philips L9.2EAA, Service Manual

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