On Screen Display Functions - Sony D98 chassis Operation Manual

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 CN305.
- Heater voltage is correct and present at the heater cathode.
- Diode shorts at the cathodes.
- Sync timing signals are present at the output of IC008.
- That there is I2C communication to IC001.
2) If the screen is lighted with no video check:
- Control, blanking and clamp signals to IC001, IC002, and IC008.
- +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.

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 3.6V. IC003 is
controlled by the Microprocessor via the I2C bus. The sync timings necessary are V sync and H Fly. The reference oscilla-
tor is set by an 8MHz crystal X001.
Timing Analysis
Timing Analysis for the Auto Size Center function is provided by IC003. Time measurements are taken with V sync (pin6),
H sync (pin5) and Active Video (pin7). These measurements are then sent to the Microprocessor via I2C communication for
size and centering calculations.
A/D Conversion for Color Restoration
Coloration can be achieved by measuring the CRT beam current during the blanking time. This current is converted to a
voltage via a sensing circuit. This voltage is converted to a digital format by the Analog to Digital converters contained in
IC003. There are three A/D converters for the RGB beam current feedback (BCF) circuits. These digital representations of
the RGB beam currents are stored in the BCF Red, BCF Green, and BCF Blue registers at the time white balance is finished
on the production line. In the field the Color Restoration can be achieved by sampling the RGB beam currents again and
comparing these new values to the ones stored in the BCF registers. The Microprocessor then adjusts the cutoff voltages
until the measured beam current is equal with the values stored in the BCF registers. This function is not done automatically.
It is necessary for the end user to activate this function through the OSD menu from the front panel controls.
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(Note: Pin 18 will read 3.6V)
- V Sync and H fly signals are at pins 4 and 7 of IC003 respectfully.
- That Crystal X001 is oscillating (8MHz).
- That there is I2C communication to IC003.
2) Auto Size Center Does is not working, check:
- That +5V is supplied to IC003.
- V Sync, H Sync, H fly, and Active Video signals are at pins 6, 5, 7 & 8 of IC003 respectively.
- That Crystal X001 is oscillating (8MHz).
- That there is I2C communication to IC003.
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