RFT b/w tv with no video information

[tube tv fan]

Hi everyone! I am new here and sorry for my bad english (I am Greek).
I am having trouble with an rft donja 202 black and white tv. I have replaced all the paper and electrolytic capacitors (I tested them with 300 volts before puting them in), I checked all the ceramic capacitors and ALL the resistors. The tv has crystall clear audio, has static on the screen but when I tune in only the audio tunes. The picture turns from snow into a raster during tuning and starts showing fade jumping dots and bars according to the movie action, but absolutely no video information is visible. Since it is tuning, the tuner is not the case but I tried with an exactly same tuner from a donor set and of course this made no difference. I also tried with different converter boxes. In a last attempt, I opened all the video IF cans and checked everything in them. All good. Finally, all the tubes were tested and most of them have been replaced. The only weird things I found is that the 100K potentiometer called "W125" does absolutely nothing to the picture. I measured it and it is good. I did not measured the center pin though. The second weird thing is that the contrast potentiometer pulls the sound down when it is turned down. I changed it and it made no difference. The weirdest thing is that it pulls the sound down according to the antenna signal. With no signal, it does not affect the sound. Now I am completely lost. Has anyone ever experienced a problem like this?
I am going to attach the schematic.