Finally, I was able to get a video image! I’ve spent the past 2 weeks fighting with a problem that I had started to think that I would never have been able to solve it. Every test I did i simply got a “no input signal” alert from my TV, not understandig what was going on. In the last 2 days I’ve spent a lot of time measuring the output clock on the COMCLK pin of the video chip, getting a very unstable frequency, going from 1.8MHz to 3.58MHz without an apparent reason. I changed a lot of parallel crystal capacitors, trying different values with no result. I tried to connect the signal pin directly to the TV or using a buffer but nothing changed. Finally, today I had the idea to check the voltage of the power supply. I found 4.7V near the voltage input but a shocking value of 3.7V at the other side of the circuit! I finally understood that the problem was the breadboards daisy-chain: 6 breadboards are not as good as you think… Another reason was the poor quality of my power supply. So I quickly put an LM317 and got a very stable voltage of 5.04V on most of the circuit. The result is shown in the picture below: my LED TV is showing the video signal generated by the TSM9918A. Schematics will follow soon.
LM80C – first image
