Mitsubishi V19-V21, Техническое руководство

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6-6
Figure 6-5 shows the V-Chip Blocking circuitry in the
V19. Main picture V-Chip circuitry is in the TV µPC.
Main picture Y signal is input to IC7A00 at pin 100.
The current program rating is read and if necessary the
µPC blocks the program.
IC7V01 is used to monitor the rating of the sub pic-
ture signal. Sub picture video is input to IC7V01 at
pin 7. The internal circuitry reads the program rat-
ing data on line 21 and sends it to the TV µPC over
the Program Block line. If that particular program
rating has been blocked the µPC blocks the sub pic-
ture in the 2HDW circuitry. When the sub picture is
blocked, the PIP/POP insert is black.
AC-OFF Circuit
The AC-OFF circuit is not new. When a logic change
at the AC-OFF input of the TV µPC indicates an AC
power loss, the Control circuitry rapidly stores all
user programming and service adjustments in memory
before the DC supplies drop to zero.
Although the purpose of the circuitry has not
changed, the method of monitoring the AC source is
different in the V19.
Figure 6-6 illustrates the AC-
OFF monitoring circuit in the V19.
The AC signal applied to Bridge Rectifier D9A01 is
monitored. D9A01 is the DC source for both Standby
and Switched Regulators. The AC source is con-
nected to the inputs of the Bridge Rectifier, and the
circuit is reference to a Hot ground.
The signals at the rectifier inputs, in reference to the
Hot ground, are AC sine waves 180 degrees out of
phase. Both signals are resistive coupled to the base
of Q9A54. Diode D9A28 removes the negative half
of each signal. The resulting positive half cycles of
each sine wave keep the transistor conducting.
With Q9A54 On, the LED and Photo Transistor in
PC9A21 conduct, holding Q7B90 On. This holds
the AC-OFF input of IC7A00 Low. If an AC power
loss occurs, Q9A54, PC9A21 and Q7B90 stop con-
duction. This allows pin 20 of IC7A00 to go High,
indicating AC power has been lost.
When this occurs, the TV µPC outputs a momen-
tary High at pin 82, which is directed to the DM
Module. This is the Power Good line, informing the
DM Control circuitry of the power loss.