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Since this appeared after you had the board replaced, I first would suspect grounding of the aquadag, (the outer coating of the CRT), which would cause lines similar to what you describe, especially when the brightness is high. Zenith sets are known to have several ground wires that have snap on to 1/4 inch ground terminals, that usually mount to different brackets on the tuner, other boards, and the shield around the CRT. There might be a ground wire hanging loose that wasn't hooked up at the time the board was replaced. Also possibly some corona (high voltage) discharge around the CRT anode connector, or wires dressed too close to the flyback (high voltage) transformer. Take the back off and listen for any high voltage arcing or hissing, indicating high voltage discharge (corona). Make sure the ground wires are plugged in and on around the shield that goes around the picture tube. You also could try removing the suction cup, the high voltage connector that goes on the side or top of the CRT, (heavy red wire), clean it off good and snap it back on. Since the CRT holds a charge, first discharge it by sliding a grounded screwdriver under the suction cup and usually you will hear a snap (arc) to make sure that there is no charge on the CRT before you attempt to remove it. Other wise you will get a nice little shock, as you take off the suction cup, called the anode connector. Also you could have gotten a bad main board and there could be a problem in the high voltage or horizontal section causing the vertical lines. Several things on the main board could be wrong, some being bad capacitors, arcing inside of the flyback transformer, or bad connections on the board. As far as it taking a while for the picture to clear up, that could be caused by the picture tube getting weak and tired. The picture tubes in the later sets like you have, the CRTs didn't last as well as the earlier one's such as the Chromacolor tubes. Good luck with the set. Zeniths were some of the best TVs ever made.
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