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CIRCUIT DESCRIPTION
HIGH VOLTAGE DRIVE CIRCUIT
When QN04 is turned on, the 11V standby will also be applied to the High Voltage Drive IC IH02 pin 14
via RN15 and DN13. When this occurs, the IC will stop generating the drive signal that is used to produce
High Voltage via QH08, the High Voltage Driver. Again, this is done to prevent CRT burn, especially during
sweep loss.
CONCERNING QN04
There are several factors that can affect the operation of QN04; namely loss of vertical or horizontal blank-
ing and spot killer or spot protect from a shutdown in the deflection power supply.
Loss of Vertical Blanking
When the 24Vpp positive vertical blanking pulse is missing from the base of QN01, it will be turned off,
which will cause the collector to go high. This in turn will cause QN02 to turn on, creating an increase of
current flow from emitter to collector and up through RN07, (which is located across the emitter base
junction of QN04), to the 11V standby supply. This increase of current flow through RN07 will bias on
QN04 and the events described previously will occur.
Loss of Horizontal Blanking
When the 11.6Vpp positive horizontal blanking pulse is missing from the base of QN05, it will be turned off,
which will cause the collector to go high. This in turn will cause QN03 to turn on, creating an increase of
current flow from emitter to collector, through RN06, and up through RN07. Again, this increase of current
flow through RN07 will bias on QN04 and the events described previously will occur.
SPOT PROTECT or SPOT KILLER
As mentioned earlier, when the deflection power supply goes into shutdown for whatever reason, a low
potential will be felt at the cathode of DN14, forward biasing it and causing current flow through RN07.
Once again, this increase of current flow through RN07 will bias on QN04 and the events described
previously will occur.