Philips L01H.1A, Service Manual

Circuit Description

EN 69

L01H.1A

9.

•

SEL-MAIN-FRNT-RR This is the source select control 
signal from the microprocessor. This control line is under 
user control or can be activated by the other two control 
lines.

9.7.6

Power Supply Control

The microprocessor part is supplied with 3.3 V and 3.9 V both 
derived from the ‘MainAux’ voltage via a 3V3 stabiliser (7560) 
and a diode.
Two signals are used to control the power supply:
•

Stdby_con This signal is generated by the microprocessor 
when over-current takes place at the ‘MainAux’ line. This is 
done to enable the power supply into standby burst mode, 
and to enable this mode during a protection. This signal is 
‘low’ under normal operation conditions and goes to ‘high’ 
(3.3 V) under ‘standby’ and ‘fault’ conditions.

•

POWER_DOWN This signal is generated by the power 
supply. Under normal operating conditions this signal is 
‘high’ (3.3 V). During ‘standby’ mode, this signal is a pulse 
train of approx. 10 Hz and a ‘high’ duration of 5 ms. It is 
used to give information to the UOC about the fault 
condition in the Audio amplifier supply circuit. This 
information is generated by sensing the current on the 
‘MainAux’ line (using voltage drop across R3564 to trigger 
TS7562). This signal goes ‘low’ when the DC-current on 
the ‘MainAux’ line exceeds 1.6 - 2.0 A. It is also used to 
give an early warning to the UOC about a power failure. 
Then the information is used to mute the sound amplifier to 
prevent a switch off noise and to solve the switch-off spot.

9.7.7

Tuner IF

Pin 3 of the UOC (SEL-IF-LL’_M-TRAP), is an output pin to 
switch the SAW-filter to the appropriate system.
•

If UOC pin 3 is ‘low’, the selected system is:
–

West Europe: PAL B/G, I, SECAM L/L’

–

East Europe: PAL B/G

–

Asia Pacific: NTSC M

•

If UOC pin 3 is ‘high’, the selected system is:
–

West Europe: SECAM L’, L’-NICAM

–

East Europe: PAL D/K

–

Asia Pacific: PAL B/G, D/K, I

9.7.8

Protection Events

Several protection events are controlled by the UOC: 
•

BC protection, to protect the picture tube from a too high 
beam current.  The UOC has the capability of measuring 
the normal back level current during the vertical flyback. So 
if for some reason the CRT circuit is malfunctioning (i.e. 
high beam current), the normal black current will be out of 
the 75 

µ

A range, and the UOC will trigger the power supply 

to shut down. However, this is a high beam-current 
situation, the TV screen will be bright white before the set 
is shut down.

•

E/W protection, two protection mechanisms are built in, 
over-current and over-voltage. 
–

In case of over-current due to defective parts in the line 
deflection output stage, a high current will flow through 
resistors 3405//3406. If this current is large enough to 
create a voltage drop of 0.7 V across 3405//3406, 
transistor TS7606 (in A7 diagram) will conduct and pin 
80 of the UOC will be pulled down. Thereafter, the 
UOC will shut down the power supply. In case of further 
current increase, the fused resistor 3411 is built-in for 
double protection. 

–

In case of a high voltage appearing across capacitor 
2401 (dependent of the tube size), which is high 
enough to trigger zener diode 6401 into conduction, 
transistor TS7606 (in A7 diagram) will conduct and 
UOC is triggered to shut down the power supply.

•

I2C protection, to check whether all I

2

C IC's are 

functioning.

 
In case one of these protections is activated, the set will go into 
‘standby’.
 
The ‘on’ and ‘standby’ LEDs are controlled via the UOC.

9.8

Abbreviation list

2CS

2 Carrier (or Channel) Stereo

ACI

Automatic Channel Installation: 
algorithm that installs TV sets directly 
from cable network by means of a 
predefined TXT page

ADC

Analogue to Digital Converter

AFC

Automatic Frequency Control: control 
signal used to tune to the correct 
frequency

AFT

Automatic Fine Tuning

AGC

Automatic Gain Control: algorithm that 
controls the video input of the feature 
box

AM

Amplitude Modulation

AP

Asia Pacific

AR

Aspect Ratio: 4 by 3 or 16 by 9

ATS

Automatic Tuning System

AV

External Audio Video

AVL

Automatic Volume Level

BC-PROT

Beam Current Protection

BCL

Beam Current Limitation

B/G

Monochrome TV system. Sound 
carrier distance is 5.5 MHz

BLC-INFORMATION

Black current information

BTSC

Broadcast Television Standard 
Committee. Multiplex FM stereo sound 
system, originating from the USA and 
used e.g. in LATAM and AP-NTSC 
countries

B-TXT

Blue teletext

CC

Closed Caption

ComPair

Computer aided rePair

CRT

Cathode Ray Tube or picture tube

CSM

Customer Service Mode

CTI

Colour Transient Improvement: 
manipulates steepness of chroma 
transients

CVBS

Composite Video Blanking and 
Synchronisation

DAC

Digital to Analogue Converter

DBE

Dynamic Bass Enhancement: extra 
low frequency amplification

DBX

Dynamic Bass Expander

D/K

Monochrome TV system. Sound 
carrier distance is 6.5 MHz

DFU

Direction For Use: description for the 
end user

DNR

Dynamic Noise Reduction

DSP

Digital Signal Processing

DST

Dealer Service Tool: special remote 
control designed for dealers to enter 
e.g. service mode

DVD

Digital Versatile Disc

EEPROM

Electrically Erasable and 
Programmable Read Only Memory

EHT

Extra High Tension

EHT-INFORMATION

Extra High Tension information

EU

Europe

EW

East West, related to horizontal 
deflection of the set

EXT

External (source), entering the set via 
SCART or Cinch

FBL

Fast Blanking: DC signal 
accompanying RGB signals

FILAMENT

Filament of CRT

FLASH

Flash memory