Why did the TV set show up the retrace lines randomly ?
When I developed a TV project, something strange really bothered me for weeks. The CRT (Cathode Ray Tube) TV project was based upon a Philips 8051 TV microcontroller with on-chip OSD (On Screen Display) and Tuning features. The software was running on my emulator without any problems. So our customer decided to launch pilot production. The QA team found something strange in the internal audit procedure and notified me urgently. Among 12 TV sets, about 5 TV sets randomly showed the retrace scanning lines after AC switching on. The occurrence was unpredictable. A picture is “drawn” on a television display screen by sweeping an electrical signal horizontally across the display one line at a time. The amplitude of this signal versus time represents the instantaneous brightness at that physical point on the display. At the end of each line, there is a portion of the waveform (horizontal blanking interval) that tells the scanning circuit in the display to retrace to the left edge of the disp
