Panasonic CT-36G24A Horazontal Hold

Question

I have a Panasonic Model CT-36G24A Chassis No. AP332. The horizontal hold is not working properly. Sometimes when the set is turned on the horizontal is ok and sometimes it is compressed down to 3 inches. When the front panel is tapped it corrects itself. It holds sometime and sometimes not.Does anyone have a idea what the cause is? A cold solder joint , a dirty pot etc. And if possible the location of the suspect.