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home>>Tech Articles>>Tech Article #2
"A Tour of the Marquee CRT Chassis" CLM and Power-Up
Our prior article was a general explanation of how CRT projectors work, generically. Since our specialty here at E-Tech Systems is refurb of Marquee systems for home use, let's dive in to some specifics of what each Marquee module does, starting with the brains and power sections.
The Control Module (CLM), located on the lower left rear panel of the Marquee,

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provides user interface to the system as it listens for and executes IR, wired keypad and RS232 controller commands; provides pulses and logic levels to activate the low voltage and high voltage power supplies; receives and stores all settings not resident in the backplane memory chip; monitors the chassis for faults and failures such as H. Fail and V. Fail; executes on-screen displays and test patterns through the Video Input Module (VIM), and provides diagnostic readout via Ready and Diagnostic LEDs.
Functions and features are entirely software controlled, and earlier Marquees can be chipped up to add useful features such as horizontal linearity control, which was first offered in v3.3.

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Aside from mechanical lens setup and individual width coils on the horizontal sweep module, all other setups are in menus and are saved digitally on the CLM and a memory chip on the backplane.

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Three Status Readout pages are available by pressing the * button on the keypad, the pages offer much information such as projector serial number, input and recall being displayed currently, scan rate of incoming signal, and more than twenty-five other parameter values.

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Also visible in Pic #2 are the Deflection Processor (DPB) and Stigmation Waveform (SWB) boards, mounted atop the CLM on spacers. The DPB controls many functions such as incoming horizontal and vertical frequency detection, generation of H. and V. Drive signals to those sweep modules, generation of clock and waveform timing pulses, and control of Horizontal Band Switching of the Horizontal Deflection Module (HDM) which will be described in more detail later. The SWB converts zone stig correction values into waveforms that are fed to the Stig Amp on the rear heat sink for amplification to drive the stig coils inside the focus yoke, of which there are one on each tube neck; thus allowing for zone dot shape correction and the tightest possible focus out into the corners of the image. The CLM draws +5 volts and +12 volts from the low voltage power supply, to power the I/O processor and memory ICs and to power the IR receiver and the wired keypad, if installed. On Marquees built after 1994, the wired keypad is easily removed and configured for IR battery operation by moving a small jumper in the battery compartment and adding four AA batteries. Also provided for in software is the A or B selectable IR language or protocol; the keypad may be configured by moving the fourth jumper, and then one can select A or B or Both IR languages, as well as IR Off, in the Utilities menu (UTIL, 6 (Remote Control Options), 1 (Keypad Options), 1 (IR Sensor A, or B, or Off) and also for the Remote Jack on the CLM rear panel, which can accept a remoteable IR sensor, remote wired keypad, or a third-party projector system controller such as AMX or Crestron. A power-up sequence goes like this. The CLM has standby power anytime AC power is available, so the user with his/her IR keypad holds down the Power button for a few seconds, the CLM interprets the command and brings up the low voltage power supply (LVPS), the LVPS outputs +390 volts to power the high voltage power supply (HVPS), the CLM monitors for presence of horizontal and vertical sweep, and when all is up the HVPS inhibit is released to enable 34.9KV at the anodes to drive the CRT beams. One dare not have beam current without full sweep, or the tube phosphors would be instantly scarred and require costly replacement. The tubes are also protected at shut-off by the Spot Kill function; spot kill detects the Off keypad command and also H or V Fail, and kills G2 bias to the guns and slams the cathodes to blacker than black. If you see beam after power-off on any CRT system it should be serviced immediately or the tubes are at risk. Some other fascinating things also happen at power-up. The internal data bus across the backplane takes an inventory of every installed accessory installed in or connected to the Marquee, including what input cards are installed in the rear slots, what options are installed, such as AutoConverge or Contrast Modulation, and notes if a Marquee switcher or switchers (up to nine switchers with nine inputs each) are connected [see Pics Six and Nine].

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The CLM also has remembered what the last selected source was, brings that source up for display, and pulls up settings from that memory and braps out commands to the other modules to set the stored raster height, raster width, raster geometry, color temp, brightness, contrast, and convergence parameters. The CLM also resets these and other parameters on the fly whenever another source or recallable memory is selected. One very useful software feature in the Marquee is source and parameter selection using Channel Numbers. A Channel Number can be created in the Utilities Menu (UTIL, 2), and is a shortcut to selecting an input port by itself, or an input with the input memory replaced for now by a spare undedicated memory, or Recall Memory.

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Lets imagine that you want to pull up your scaler, it is physically cabled with RGBHV coax lines to Input 01 on the back panel of the projector, and the DVD you wish to watch is anamorphic and requires short raster settings to display it correctly. There are two ways to do this; you can push keypad buttons "Source", then "0", then "1" to view the source connected to the 01 Input, then wait a moment and then push "Recall", and "0" and "3" to pull up the DVD anamorphic setup saved last in recallable memory 3, but that is six button presses, and in a dark room you are likely to spill your drink all over the place! Instead, it is far simpler to go into the Channel Numbers table, select a channel not yet in use (1 thru 99) such as CH 03 and, using arrow keys, name the signal as "DVD 16:9", using Slot 01 (RGBHV) and Recall 03. Now you can replace six button presses with "0, 3" and not spill a drop. If all your signals can be managed with nine or fewer channels then you can press UTIL, 5 (Preferences), and 4 (Channel Select, 1 or 2 Digits) and select single digit channel selection, then you need only press 3 to bring up DVD 16:9. When selecting channels, the on-screen display even tells you the signal by name as you entered it; pretty cool!

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We shall continue our Marquee Projector Tour in the next installment!
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