Date: 10/02/98 R7621055
RGB Input Aut Sync Track
R7621055
6
TECHNICAL DESCRIPTION SECOND RGB INPUT 76 21055
Introduction.
With this board a second RGB analog input can be selected through the D9 (former TTL
input) connector next to the first input . Since this board occupies the former TTL
connector, the sync polarity must be corrected automatically and the board must also
select automatically between Sync on Green and Separate Sync.
In case of a separate sync input HS the sync width pulse is also set to 1/13th of the
line period.
The R, G and B output signals are sent to the RGB INPUT + SW module. The sync
outputs VS OUT (if any) and / or the HS / Comp Sync are sent to the VERT DEFL board
for further processing.
Red, Green and Blue
Inputs.
Three identical differential amplifiers are switched to active with the ON voltage. This
ON voltage is obtained from the +PORT 3 voltage arriving at contact 28 (=TTL
voltage) and the transistors Q50 and Q53. Note that the 75 Ohm termination is not
switchable.
The
Red
signal is taken from the collector of Q2 and fed to the current driver Q4. The
collector resistor of the latter is on the RGB SW + Input board. G OUT and B OUT are
got in a similar way.
The green signal is also sent to Q60 and used for synchronisation if Sync on Green
has been detected (see further).
The blue output at Q23 is also supplying Q15. When the Blue in Green switch S2 is
in a closed position, Q16 is blocked and Q15 adds some amount of blue into the green
channel via D25 . If however S2 is open Q16 is saturated and Q15 does not get enough
base voltage and is consequently blocked.
Note : The Blue in Green of the first analog input is switchable via the remote control,
thus via software control. Here, the blue in green is switched with S2 and is not affected
by the software.
If separate vertical sync pulses are available and applied to the Q41 / Q43 input they
arrive on the Q39 amplifier / inverter. The inverted pulses are now inverted or not inverted
depending on the voltage level of pin 12.
Assume the pulses at the drain are positive. Then Q46 is regularly switched on by these
pulses and the average voltage at the collector or at pin 12 is low. In such case the
output pin 11 follows the input pin 13 , which means that the pulses are positive at pin
11.
If the pulses are of a negative polarity at the drain, Q39 never gets in conduction and
the level at pin 12 is high through R127. The input pulses are inverted by the exclusive
OR gate.
The polarity of the pulses at pin 11 is thus always positive irrelevant of the input polarity.
These pulses are proceeding to the base of Q47 via D54 and to the multiplexer /
demultiplexer 4053B, pin 11. The +RGBS voltage provides the necessary biasing for
Q47.
The 4053B is triple two-channel multiplexer, having three separate digital control
inputs. One of these control inputs is pin 11.
If VS pulses are applied to the input, then the HS/CS output must be the HS input. The
selection between HS or CS happens in the second multiplexer. On other words, as
soon VS pulses are applied, the HS pulses must also be selected.
The presence of the VS pulses determine the correct voltage at pin 9 in order to select
the pin 3 input (Shaped Horizontal Sync).
Vertical Sync Input - Auto-
matic Polarity.
Technical description
Summary of Contents for GRAPHICS 1209S
Page 4: ...BARCO PROJECTION SYSTEMS GRAPHICS 1209S 90 00972 230V AC 90 00977 120V AC SAFETY NOTICE...
Page 9: ...BARCO PROJECTION SYSTEMS GRAPHICS 1209S 90 00972 230V AC 90 00977 120V AC GENERAL INFORMATION...
Page 28: ...BARCO PROJECTION SYSTEMS GRAPHICS 1209S 90 00972 230V AC 90 00977 120V AC SERVICE SHEETS...
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