This sounds like another case of the classic C926 capacitor becoming defective, this being associated with the vertical scanning drive circuit. As you restricted your e-mail address do a Google on C926 and you should pick up plenty of info as this affects a large range of models across the JVC ranges of that era. Your user manual should you be meaning that? wont mention anything about this nor would a service version, as JVC never acknowledged a problem existed albeit its a widespread one.