Philips MG5.1E, Service Manual

Page: 69 / 83

MG5.1E 7. CRT Drive Circuit 69
Personal notes
7. CRT Drive Circuit
Figure 7-1
10
9
8
7
6
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1
5
10
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9
7
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4
2
1
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G1
GND
GND
RED
+12V
FIL HI
FIL LO
IKR
NC
+240V G1
BLUE
GND
GND
IKB
+12V
FIL HI
FIL LO
NC
240V
1 2 3 4 5 6 7 8 9 10
10 9 8 7 6 5 4 3 2 1
IKR GND RED GND GREEN +12V BLUE GND IKG IKB
RED
CRT
PANEL
BLUE
CRT
PANEL GREEN
CRT
PANEL
INTERFACE PANEL
1 2 3 4
+240V NC FIL LO FIL HI
TO SCAN
HV PANEL
1883
1882
1881
1884 1894
1871
1083
CL 96532100_094.eps
121199
Red, Green, and Blue drive from the Small Signal panel is fed
to the CRT drive circuit on the Interface panel. (Figure 7-1) Red
drive is fed to transistors 7015 and 7016. Green drive is
amplified by 7018, and 7019. An additional amplification circuit
is added to the Blue circuit to provide added gain. This is called
the Blue Stretch circuit. This circuit consist of transistors 7022,
7023, and 7031
Transistors 7017, 7020, and 7024 provides CRT blanking. In
the event of a Sweep failure, the High on the CRT protection
line from the High Voltage Scan panel will go Low. Diodes
6011, 6012, and 6013 will then be forward biased through
resistor 3026 which will turn the blanking transistors On. Diodes
6009, 6006, and 6010 are forward biased when the Horizontal
or Line Sync from the High Voltage Scan panel goes Low.
During Convergence alignment, individual CRT's are blanked.
Thi is accomplished by the DAC 7001. Pins 9, 10, and 11 of the
IC are pulled Low to blank individual CRT'S. This IC is
controlled by the Data (SDA) and Clock (SCL) lines from the
Small Signal panel.
The Red, Green and Blue Drive is fed to the Green CRT panel
along with a 12 volt bias. (Figure 7-1) Red and Blue drive from
the Green CRT panel is routed to their respective CRTS.
Filament voltage and the 240 volt CRT drive voltage from the
Scan High Voltage panel is fed to the Green CRT panel. Beam
Current information IKR, IKG, and IKB are fed back to the
Interface panel where they are combined into BCINFO before
being fed to the Small Signal panel. Circuits on the Small Signal
panel automatically adjust the CRT bias to maintain the correct
white balance.