Panasonic EURO 4 Chassis, Техническое руководство

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Chapter 4 EURO 4D Supplement
:
Pin 67 - IRef
This is a reference current for internal PLL.
:
Pin 68 - CVBS In
This composite video signal which is input via
pin 68 is used for teletext processing which is carried
out within the microprocessor IC1101.
:
Pin 71 - VProt
This input is used to detect a fault in the deflection
circuit. This is achieved by using the vertical
synchronisation
signal which is fed to the
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
safety input of the microprocessor IC1101 is
in-operative.
Where an error occurs resulting in there being no
vertical synchronisation 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 user commands for control of the TV receiver are
applied via the remote control.
These commands from the remote control transmitter
are applied via RPM-637CBRL IC1061 the remote
control receiver and Q1051 to pin 74 of IC1101, this
command data being in serial format.
:
Pin 75 - Prot1 12.
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:
1. ABL protection
During normal operation the beam current is
measured, with the result being input via the sense
input of VDP IC601, pin 28.
The beam current limitation is carried out via software
control with the results of this being used to back off
the RGB output amplifiers in this I.C. to a greater or
lesser extent, thereby limiting the beam current.
Where the control limit is exceeded, although 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
the microprocessor IC1101 is pulled LOW.
Where upon, after a short delay the microprocessor
IC1101 switches the TV into standby.
2. Voltage supply lines protection
The Voltage supply lines monitored for short circuit
faults, are:
:
12V supply monitored via D863
:
8V supply monitored via D865
:
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.