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home>>Tech Articles>>Tech Article #3
Installment Three: "A Tour of the Marquee CRT Chassis" How Adjustments Are Executed
We discussed in Installment Two how the Control Module provides user interfaces in software, manages chassis power-up, and gives the means to adjust parameters and stores the settings after. Some parameters have sufficiently frequent useage that the IR keypad (see PIC 1) provides specific buttons for those adjust- ments, such as Contrast, Brightness, Source, Recall, and digits to use in selecting Channel Numbers. Other adjustments require entering a menu such as Picture (PIC) or Geometry (GEOM) or Convergence (CONV) and then selecting from a list. When a parameter is selected for adjustment, such as Contrast, the on-screen display gives a slidebar a nd a numeric readout (see PIC 2) of the Contrast value from 0 to 100, and also a prompt for which arrow keys to press to effect the adjustment.

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The PIC menu (see PIC 3) lists out as follows:
PIC 1 Horizontal Phase (left or right arrow key to adjust) and also Vertical Phase (up or down arrows), the phase adjustments are used to center the displayed image on the screen. Phase is a sync pulse delay between incoming sync and drive signals for H. and V. sweep.
PIC 2 H. and V. Size set how big the raster is; the Control Module (CLM) sends digital values to the sweep modules to optimize raster size for different aspect ratios. The Horizontal Deflection Module (see PIC 4) is mounted in an upright metal sleeve between the green and blue CRTs and supplies pulses to the horizontal sweep yoke, the gray bell-shaped device with yellow tape (see PIC 5), mounted on each tube neck. The white tubes with copper windings seen in PIC 5 are the individual width coils with ferrite slugs; a low-band adjustment for each color is provided (below 59.5khz scan) and one for high-band for each color, six width coils in all. The idea is to match red, green and blue raster widths in the sweep section, raster heights also, as to place the least workload on the dynamic convergence amplifier, for minimal convergence drift. The horizontal drive pulses to the yokes exceed 1000 volts depending on H. Size settings and scan rate, we show the scoped pulses (see PIC 6) by holding the scope probe just above the width coils so as not to damage our oscilloscope. The Vertical Deflection Module (see PIC 7) generates a less hazardous 35 volt waveform (see PIC 8) that can be scoped (see PIC 9) at the yoke output connector going to each sweep yoke. The VDM often requires modification to achieve shorter raster heights for anamorphic or HDTV display. (see PIC 10)

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PIC 3 White Balance; select from global presets for 3200K, 6500K or 9300K, or a unique User Setting for each separate memory, or a Customize White slider that takes color temp to points in between 3200K, 6500K and 9300K. Color temperature deals with what a "white" scene should look like if lit only by a tungsten filament heated to various high temperatures; lower color temps are in the orange region, 6500K is white for film purposes, 9300K is into the bluish region.
PIC 4 Focus; varies spot size with waveforms sent to the focus module, which provides current to the focus yokes to vary the spot size across different areas of the tube face. The sides and corners of the essentially flat tube face are farther from the electron gun than the center, hence the need to correct for this distance variance with a parabolic correcting waveform to the focus yoke.
PIC 5 Slow/Fast sync; this varies a time constant in the H Sync processing to reduce flagging on VCR signals with sloppy sync.
PIC 6 Blanking, allowing the user to electrically mask any edge of the raster; often used to mask captioning blips in the vertical interval or head-switch noise on a VCR signal.
PIC 7 AutoClamp On/Off; restores correct black level to green if sync-on-green is fed to the unit in earlier Marquees, the feature is left on full time in later software versions.
PIC 8 Retrace Long/Short; the user can speed up retrace if unable to display both the left and right edges of a signal.
PIC 9 Decoder Options; selections to optimize a Marquee multi-standard decoder module if used. A user may select AutoDetect or NTSC, PAL, or SECAM, and may select routing of an S or composite feed through the RGB ports if necessary.
The Geometry button pulls up a menu (see PIC 10) for settings that vary raster size and shape:
GEOM 1 Horizontal and vertical raster size adjustments. The amplitude of the sweep waveforms from the horizontal and vertical deflection modules are varied to deliver the required voltage and current for appropriate raster size. Most Marquees require resistors to be changed or added to enable short anamorphic raster sizes for DVD and HDTV display.
GEOM 2 Keystone adjustment permits adjusting the top of the raster to be narrower or wider than the bottom to compensate for shooting at an up angle from a table to the screen, or from a down angle in a ceiling mount situation. A waveform from the vertical sweep is fed to the width requlation section of the HDM to modulate the horizontal yoke current in timing with vertical refresh.
GEOM 3 Side pincushion adjusts raster edge curvature, width again is modulated from raster horizon versus top and bottom edges.
GEOM 4 Top pincushion is curvature along the top part of the raster and this correction is delivered by varying timed waveforms through the convergence section.
GEOM 5 Bottom pincushion, curvature of the bottom edge delivered through convergence.
GEOM 6 Vertical bow, curvature of the horizon or mid-raster, delivered through convergence.
GEOM 7 C linearity corrects for equal scan line spacing from top to bottom and equal scan velocity from left edge to center to right edge, so the squares of the test pattern grid can be made equal height and width anywhere in the raster; vertical linearity is done through shaping of the vertical sweep waveform to the sweep yokes; horizontal linearity is delivered through convergence.
GEOM 8 S linearity, similar to C linearity but affecting center-to-edge.
GEOM 9 Horizontal skew, correction to make vertical lines run parallel to the screen edges, delivered through convergence.
Pressing the Convergence key brings up a menu (see PIC 11) giving selection of different adjustment routines allowing Green Convergence for raster squaring, and full regular convergence routines to enable precise overlay of red and blue rasters to the reference green raster; once into a routine the user can select from standard crosshatch, fine crosshatch, or converge while viewing an external signal by pressing the # key; this is invaluable in aligning stacked projectors to a common test signal; convergence waveforms originate in the Control Module and are amplified in the Convergence Amplifier section, the middle section of the rear heat sink (see PIC 12).

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CONV 1 Guided routine, red and blue are positioned and shaped to match green; both static (full-frame) and dynamic (zones not in the center) are adjustable by entering the routine, making adjustments at each step with the arrow keys, and advancing around the screen by pushing the Enter button. The user can exit at any step of the routine with a few presses of the Exit key, and he is asked by the OSD if he wants to save changes, discard changes, or continue adjusting. Static convergence is delivered with DC offset voltages into the sweep yokes, dynamic convergence is delivered by waveforms originating in the control board and amplified by the convergence \amplifier on the rear heat sink. This section generates considerable heat and must be afforded adequate ventilation as it has no fan along the rear.
CONV 2 Interpolated routine, used mostly for initial setup; the user is guided around the screen using the Enter key, but larger areas of raster are adjusted early in the routine, narrowing down to smaller zones later.
CONV 3 Random Access routine lets the user steer the adjustment zone cursor straight to the area needing alignment, thus saving time to go in and adjust a side or corner. The Enter key toggles between moving the cursor with the arrow keys and adjusting at the point needing attention; the Color key selects between red or blue as the color being adjusted.
CONV 4
Allows launch of AutoConverge if installed; the Marquee can align itself in 45 zones in three minutes per memory, using a motorized front panel sensor and a logic card installed in a slot above the control board. (see PIC 13)

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CONV 5 Service menu, passcode protected (0901); this gives access to Green Convergence and some Acon-specific alignments (see PIC 14)

CONV, 5, 1 Green interpolated convergence, large-scale raster shaping across multiple zones at each point in the routine.

CONV, 5, 2 Green random access, to go to a specific zone using arrow keys.

CONV, 5, 3 thru 7 -- blank unless the Acon kit is installed, (see Pic 15) then you see:

CONV, 5, 3 Acon offset; the Acon tries to align red and blue to green in the center; the user can add correction to any error and the system remembers the amount and direction of correction needed to enable future accuracy.

CONV, 5, 4 Acon Auto Learn Screen; the Acon system displays green blocks all over the screen and determines where the screen edges are, and stores this data in the control module.

CONV, 5, 5 Manual Learn Screen; the user can enter screen edge locations manually

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Our Marquee Chassis Tour will be continued in the next installment.
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