Hey folks
First of all
thanks for
phenomenal advice.
I do have plastic screwdriver so I used it while having oscilloscope turned on.(but I am also going to make a wooden one, I actually do need it, never thought of using those barbecue sticks)
I was able to adjust channel B by moving R16 pot and doing what
danadak suggested, and I was able to
successfully fix the problem with channel B.
However, channel A still has the same problem no matter how much I adjust the pot, in fact I don't think the pot had any effect at all.
As far as is it intermittent, seems its not and I did clean out potentiometers few days ago when I noticed there were some problems while moving the knobs slowly like signal skipping or jittering, those problems disappeared after cleaning.
edit :
I went back to check channel A little bit more in detail, and I noticed that I can not raise the signal beam above certain point almost like there is a ceiling the signal is hitting and can not go above, and if I move the R16 pot on channel A board, it seems it just changes where this imaginary ceiling is.
Even using vertical adjustment knob won't allow me to go above this ceiling.
Here is the video to demonstrate : (uploading)