Philips L01.1A Service Manual Download

Page: 43 / 88

Circuit Description

GB 83

L01.1A

presence of an external Y/C source makes this line ‘high’
while a CVBS source makes the line ‘low’.

•

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

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

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