Television 1960s 23" Weltblick 511TR

[Electronic M]

It would appear that your sets vertical deflection circuit is operating at twice the proper frequency....It can obviously still synch but it is scanning the top half of the frame over the bottom half. I had this exact issue before once. What you need to do is replace all capacitors in the vertical circuit, and test all the resistors in the vertical to make sure all are within rated tolerance (if any are not in tolerance replace them obviously)....If that does not fix the issue, then get a resistance decade box and start trying different values in place resistors in that are in that circuit (which is what I had to resort to).

As for the brightness make sure the HV is correct, and the cathode grid and screen voltages are right. If any are wrong track down the problem in the circuits supplying it.