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DA100 (50Hz) Chassis – Article for Television Magazine
are blanked. This feature can be selected by software.
The safety input pin has two thresholds. Between zero and the lower threshold, normal functioning
takes place. Between the lower and the higher threshold, the RGB signals are blanked. Above the
higher threshold, the RGB signals are blanked and the horizontal drive is shut off.
Both thresholds have a small amount of hysteresis. The main oscillator and the horizontal drive
circuitry are run from a separate (standby) power supply and are already active while the television is
powering up.
Note that in this chassis the standby supply pin is connected to VCC.
The safety input pin has two thresholds. Between zero and the lower threshold, normal functioning
takes place. Between the lower and the higher threshold, the RGB signals are blanked. Above the
higher threshold, the RGB signals are blanked and the horizontal drive is shut off.
Both thresholds have a small amount of hysteresis. The main oscillator and the horizontal drive
circuitry are run from a separate (standby) power supply and are already active while the television is
powering up.
Note that in this chassis the standby supply pin is connected to VCC.
Scan Velocity Modulation Output
This output delivers the analogue SVM signal. The Digital to Analogue Converter is a current sink like
the RGB Digital to Analogue Converters. At zero signal level the output current is 50% of the maximum
output current.
the RGB Digital to Analogue Converters. At zero signal level the output current is 50% of the maximum
output current.
Protection – Video/Sync Processor
The video/sync processor (IC801) contains protection circuit that can monitor the scanning circuits
operation.
operation.
Safety
On pin 12 of IC801, EHT is calculated by measuring the rectified horizontal fly-back pulse. D615 and
C617 rectify and smooth this supply, D617 limits the bias at pin 12 (under normal conditions this
voltage is less than 1V). There are two thresholds once the first threshold has been met the RGB
drives are blanked. If the D.C. voltage continues to rise and passes the second threshold, then the
horizontal drive is stopped so that forward X-rays are not emitted.
C617 rectify and smooth this supply, D617 limits the bias at pin 12 (under normal conditions this
voltage is less than 1V). There are two thresholds once the first threshold has been met the RGB
drives are blanked. If the D.C. voltage continues to rise and passes the second threshold, then the
horizontal drive is stopped so that forward X-rays are not emitted.
Vertical Protection (VPROT)
This pin monitors the operation of the vertical output stage. The vertical fly-back pulses are applied
to pin 11 (this is a 50Hz, 5V peak pulse). This signal is taken from the vertical flyback generator
circuit (Q502 and Q503). If the negative edge of this signal cannot be detected then the RGB drives
are blanked.
to pin 11 (this is a 50Hz, 5V peak pulse). This signal is taken from the vertical flyback generator
circuit (Q502 and Q503). If the negative edge of this signal cannot be detected then the RGB drives
are blanked.
Figure 56: VDP Protection Circuits
Page 58 of 80
Sharp Electronics (UK) Limited - March 2003
Revision 2
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