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1. RGB Signal Processing (A Board)
RGB Signal Amplifiers
RGB video signals are amplified by IC001. Here the individual Sub Contrasts, Brightness offsets, and Contrast gain levels
are set by the Microprocessor via I2 C control. The OSD RGB video signals from IC003 are mixed into the main video
channels inside IC001. IC002 provides a final amplifier stage for the RGB video signals. This video driver is internally set
to a gain of –14. Therefore at the output pins of IC002 (Pin1, 3 & 5) the waveform is inverted with typical drives levels on
the order of 45Vpp. The Video Driver IC002 drives the CRT cathodes via AC coupling.
RGB Cathode Cutoff Amplifiers
The Red cathode DC cutoff level is amplified by IC004. It is controlled by the D/A output of IC001. The Red cutoff level
is clamped by discharging C106 via D106. The Green and Blue cathode Cutoff levels are clamped in a similar fashion. The
individual cathode cutoff levels are set for white balance by the Microprocessor via I2C communication with IC001.
Troubleshooting Hints
1) If the screen is blank with no output check:
• Video signals with proper cutoff levels are provided to the CRT cathodes.
• Supply voltages are at the appropriate levels and locations starting at CN304.
• Heater voltage is correct and present at the heater cathode.
• Diode shorts at the cathodes.
• There is I
C communication to IC001.
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2) If the screen is lighted with no video check:
• Control, blanking and clamp signals to IC001, IC002.
• +5V, +12V, and +80V to these circuits.
• For shorted diodes on the IC002 outputs.
3) If colors are wrong or missing and white balance cannot be adjusted check:
• Each individual color signal path comparing DC offset and peak to peak signal levels to each other to determine
if there is any single amplifier at fault.
• For shorted diodes on the IC002 outputs.
• G1 level at the cathode (-33V)
2. On Screen Display Functions
On Screen Display(OSD)
IC003 is the On Screen Display character and graphic generator. It provides RGB and Fast Blanking data to IC001 for
mixing with the main video channels when required. Outputs voltages are two dimensional, either 0V or 5V. IC003 is
controlled by the Microprocessor via the I2C bus. The sync timings necessary are H Retrace and V Retrace.
Troubleshooting Hints
1) No OSD is displayed, check:
• RGB and Fast Blanking inputs to IC001. If there are no signals then IC003 may be at fault.
• That +5V is supplied to IC003
• V FLB and H FLB signals are at pins 10 and 5 of IC003 respectfully.
• That there is I2C communication to IC003.
3. G2
Troubleshooting Hints
1) If picture is black, check:
• G2 level at the cathode using HV probe (typically 350V ~ 750V).
• Input to G2 amp, Pin 5 of IC005.
• Heater voltage at the cathode.
• +12V, +5V, and G2 voltage coming from D board.
4. Display Data Channel (DDC) Circuit
DDC2B allows the display to inform the host computer of it's identity and capability. IC906, which has memory and I
serial communication capability, is a device for DDC2B. Pin 5 and 6 of IC906 are prepared for SDA (I
(I
C clock). EDID (Extended Display Identification Data) consists of 128 bytes of data containing the display's identity and
2
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C bus
2
C data) and SCL
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