Mitsubishi Electric HITACHI VS-50111 Troubleshooting Manual page 42

V20 Chassis Technical Training
and Troubleshooting Guide
• Add side pincushion correction, controlled by
the EWDRV signal from the VCJ.
• Reduce the Deflection DC supply during
scanning frequency changes.
Figure 3 shows the Horizontal Deflection DC Supply
circuitry. The conduction of Q5A01 determines the
value of the DC Supply for the Horizontal Output Tran-
sistor, Q5A31.
The conduction of Q5A01 is controlled by Q5A06,
Q5A05, Q5A03 and Q5A02. EWDRV signal is ap-
plied to the base of Q5A06 for Side Pincushion Cor-
rection.
When the base voltage of Q5A06 decreases, Q5A01
conducts less, lowering the Horizontal Output DC sup-
ply. When is the 31.5 kHz scan mode, the 31K line
from the µPC goes High. The High drives Q5A07 into
conduction, reducing the base voltage of Q5A06, which
reduces the DC supply to the Horizontal Output.
The H-MUTE line from the µPC and Q5A08 reduce
the DC supply during scan frequency change by the
same method.
The DC supply for the Horizontal Drive transistor,
Q5A32, is derived from the Horizontal Output DC
supply through R5A36, R5A37 and Q5A34. In the
31.5 kHz mode, the DC supply for Q5A32 would drop,
since the supply for Q5A31 decreases.
To prevent this the 31K control line also connects to
the base of Q5A35. When Q5A35 is driven into con-
duction, the conduction of Q5A34 is increased to main-
tain the DC supply for Q5A32.
HV & HV Regulation
Figure 4 illustrates the HV and HV Regulation circuitry.
Drive from the Horizontal Deflection Output circuitry
is applied the HD-IN input of IC5A00. IC5A00 am-
plifies the signal which is output at pin 1, and through
Q5A07 and Q5A09, is applied to the gate of Q5A51.
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