Panasonic EURO 4 Chassis Technical Manual page 103

3DQDVRQLF
Chapter 3
: Pin 71 - VProt
This input is used to detect a fault in the deflection
circuit. This is achieved by using the vertical
synchronisation signal
microprocessor IC1101 pin 47, via transistor Q1108.
This signal is also fed via diode D453 where capacitor
C455 is charged. The charge held by capacitor C455
results in a HIGH level being applied to the base of
transistor Q451, which ensures that the transistor is
switched OFF.
When transistor Q451 is switched OFF a HIGH level
is applied to pin 71 of the microprocessor IC1101, fed
via resistor R457. This HIGH level ensures that the
saftey input of the microprocessor IC1101 is
in-operative.
Where an error occurs resulting in there being no
vertical synchronistaion signal being fedback to
transistor Q451, capacitor C455 discharges via R458
resulting in transistor Q451 conducting. This results
in pin 71 of the microprocessor IC1101 being pulled
LOW and the TV switching into standby after a short
delay.
:
Pin 74 - RC
The users commands for control of the TV receiver
are applied via the remote control.
These commands from the remote control transmitter
are applied via the remote control receiver to pin 74
of IC1101, this command data being in serial format.
:
Pin 75 - Prot1 7.
The microprocessor IC1101 pin 75 which is normally
held High via R1149 provides a protection input which
is used to switch the TV into standby mode. The
protection input has two hard wired protection
circuits, these being:
:
ABL protection
During normal operation the beam current is
measured, with the result being input via the sense
input of the DDP IC1504 pin 17, the beam current
limitation being carried out via software control.
The results of this being used to back off the RGB
which is fed to the
output amplifiers in this I.C. to a greater or lesser
extent, thereby limiting the beam current.
Where the control limit is exceeded, and the amplifiers
have been completely reversed (which may lead to an
error in the RGB final outputs or there voltage supply),
defects in the CRT may result if no protective
measures are taken.
In order to avoid this, zener diode D511 is
incorporated into the circuit.
During normal operation the zener diode D511 is
non-conducting and Pin 75 of the microprocessor
IC1101 is held High via resistor R1149. In this state the
protection circuit does not operate.
Where an error described arises and the beam
current continues to rise then the zener diode D511
conducts due to the negative voltage fed back from
T551 (Flyback transformer), which causes diode
D609 to conduct pulling the anode of the zener diode
D511 lower than its cathode. As its anode is pulled
lower, its cathode becomes more positive. Once the
zener diodes breakover voltage is reached pin 75 of
microprocessor IC1101 is pulled LOW.
Where upon, after a short delay the microprocessor
IC1101 switches the TV into standby.
:
Voltage supply lines protection
The Voltage supply lines are monitored for short
circuit faults,the supply lines monitored are:
1. 12V supply monitored via D863
2. 9V supply monitored via D864 ( wide screen only )
3. 8V supply monitored via D865
4. 5V supply monitored via D866
If a fault occurs resulting in one of the aforementioned
supplies failing then the safety diode connected to
that supply will conduct. This will result in the base of
Q851 (which is switched OFF during no fault
conditions) going low with respect to its emitter. In this
condition Q851 would conduct biasing ON Q856, this
would cause pin 75 of the microprocessor IC1101 to
go LOW and the TV would shut down into standby.
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EURO 4H Supplement