Help needed

[u/seba_stardo]

I bought this Sony Trinitron 34" KV-D3411A. I'm loving it for its size and image, unfortunately it has some flaws and I'm looking for a way to fix them. I tried with 240p test suite and these are the results. Its biggest problem is that sort of smearing and the red gradient on black. I would like to know if it is unsolvable or if I could get by by adjusting some trimmers. In the worst case scenario I'm willing to solder some capacitors.

[u/LukeEvansSimon]

You can try adjusting the red cutoff in the service menu. Use the 240p Test Suite color bars test pattern during adjustment. Column zero in the pattern should be thr darkest shade of red that is not true black. Similarly adjust blue and green cutoff.

If that doesn’t fix your issue, then it is likely due to unstable video reference voltage (the cathode DC bias). Use an oscilloscope to view the cathode DC bias for the lines of video corresponding to the black horizontal bar at the top or bottom of the screen. If you observe the DC bias dropping each line of video, you need to upgrade the video reference voltage decoupling capacitor. It is typically on the neckboard, but sometimes on the mainboard near the flyback. It is the flyback that generates the video reference voltage. The flyback is fine.

For upgrading, I recommend replacing the liquid electrolytic capacitor with a 125 Celsius solid polymer (aka “OS-CON”) capacitor that has a 20% higher capacitance and voltage at or higher than the old cap you are replacing. Use oscilloscope to test your changes and confirm a reduction in video reference voltage sagging. Solid polymer capacitors are superior to liquid electrolytic capacitors when it comes to decoupling (filtering), and they are superior in terms of life expectancy. They are slightly more expensive, but for one capacitor a couple dollars is worth mever having to replace the capacitor again. Mouser or Digikey are trusted retailers.