Circuit Description
GB 94
A10PTV2.0 NTSC
9.
Figure 9-18
Figure 9-19
9.7.5
High Voltage and Shutdown
The High Voltage circuit in the A10 PTV chassis is contained
in an integrated High Voltage Module. This circuit is powered
by the 130-volt source from the Full Power supply. The Dag
line from the CRT's is connected to 1574 and to Pin 1 of the
High Voltage module. This line along with the current sense
line from Pin 3 is connected to the Beam Limiter transistors
7905 and 7910. This provides feedback to the RGB output
circuit in IC 7301 located on the SSB panel to make minor
changes in brightness and vertical height.
When the set is turned on, the 130 volts is applied to Pin 10
of the High Voltage module. Transistor 7500 acts as an OR
gate to detect the failure of Frame Sweep (VPUL) or Line
Sweep (170V Pulse). When these pulses appear, 7500 is
turned off, allowing 7501 to turn on. This will apply
approximately 7.5 volts dc to Pin 8 of the High Voltage
module, turning it on. The High Voltage module produces 15
kV for the Focus/G2 block and 30 kV for the CRT's. This also
places a High on the CRT_PROT line, allowing the CRT drive
circuits to turn on. If Line or Frame drive should fail, CRT
drive and High Voltage will be shut off to protect the CRT's.
A failure is either drive will cause 7500 to turn On, turning
7501 Off, removing the 7.5 volts from Pin 8 of the High
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