Date : 10/02/98 R762271
Electromagnetic Focus+Hor Shift
R762271
17
Sub module
R762271S
Technical description
B. Horizontal SHIFT
The + / - SHIFT voltages are not returned to chassis ground, but to the HDL (Horizontal
Deflection Low, which is basically HTHD). Therefore, the adjusted shift voltages may
not be referenced to chassis ground, but to the same HDL.
The digital potentiometer IC (IC52) has to be supplied with the + / - SHIFT voltages from
the SMPS.
The I2C-bus lines SDA and SCL must drive the above-mentioned chip via an isolation
circuit, using an opto-coupler.
The opto-coupler IC50 is used to isolate the SDA and SCL lines, referenced to a cold
(chassis) ground, from the shift circuits in IC52.
The SCL pulses are sent to pin 1 of IC52 via an opto-coupler in IC50, whereas the SDA
data line is connected with pin 2 through the other opto-coupler in IC50.
At the moment an Acknowledgment bit is returned to the Controller, another opto-
coupler IC51 takes over. To avoid a return to IC52 via the first opto-coupler, MOSFETs
are automatically switched on and off.
The HSI (Horizontal Scan Identification) information from one of the horizontal scan
switches on the Scan Switching module, allows an inversion of the supply voltages
for the multiturn potentiometers P1 and P2. These potentiometers are the factory set
coarse alignments
of the shift, to be adjusted prior to the digital control.
The SHIFT voltages control an average DC current through the horizontal yoke windings
in order to horizontally shift the rasters.
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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