Toshiba CRT TV no sound and color calibration using a SMPTE Bars

Introduction

This tutorial provides a step-by-step guide on troubleshooting a Toshiba CRT TV with sound issues and performing color calibration using SMPTE color bars. It is ideal for anyone looking to restore their vintage CRT television's audio performance and picture quality.

Step 1: Identify Audio Issues

• Check for Sound: Turn on the TV and assess the sound level. If you hear very low sound or none at all, proceed with troubleshooting.
• Inspect Audio Circuit: Locate the audio circuit board, which is usually near the output transistors. On this Toshiba model, the board is marked as TAC8935.
• Listen Closely: With the volume turned up, put your ear close to the speaker. If you hear faint sound, the issue is likely in the audio circuit.

Step 2: Use an Oscilloscope for Testing

• Set Up Isolation: Ensure you use an isolation transformer when working on a hot chassis to prevent electrical shock.
• Probe the Circuit: Connect the oscilloscope to the output transistor and check for signal. If no signal is detected, trace back to the driver transistor and further back to the integrated circuit (IC).
• Check Capacitors: Inspect capacitors around the IC for faults. A common failure point is the L604 area where capacitors may drift in value.

Step 3: Adjust Screen Control

• Turn Down Brightness: Adjust the screen control to lower brightness to prevent a washed-out image.
• Set Picture Settings: Reset contrast, brightness, sharpness, color, and tint to the middle position to prepare for calibration.

Step 4: Calibrate Color Using SMPTE Bars

• Connect Color Bar Signal: Use a color bar generator or a video source with SMPTE color bars.
• Adjust Black Level: Focus on the lighter section of the black reference bar. Adjust the screen control until this bar is barely visible while the rest appears completely black.
• Fine-tune Picture Quality: Ensure the picture looks normal and adjust settings as necessary.

Step 5: Adjust Chroma and Tint

• Use a Blue Filter: If available, use a blue filter to isolate blue from red and green signals.
• Adjust Color Level: Increase or decrease the color level to ensure that the blue and white bars are of equal brightness.
• Fine-tune Tint: Adjust the tint setting until the colors (cyan and magenta) are equal in brightness.

Step 6: Final Checks and Reassembly

• Reconnect Any Disconnected Components: Ensure all connections, especially for the red and green transistors, are reattached before powering on.
• Power On and Test: Turn on the TV and check if the sound issue is resolved and if the picture is properly calibrated.

Conclusion

By following these steps, you should be able to troubleshoot and fix sound issues on a Toshiba CRT TV and perform effective color calibration. If problems persist, further investigation into the audio circuit or professional repair may be necessary. Enjoy your restored vintage TV for watching classic shows or playing retro games!