Hi You are describing an east west fault not really the sort of problem that a keen diyer can fix.
But If you are capable of wielding a soldering iron replace the following
REPLACE R465 10R 0.5W AND C409 10UF 100V
Please be very carefull if you are unsure DO NOT ATTEMPT TO DO THIS.
chris
April 2006
SEAMS TO TURN ITSELF OFF AFTER A COUPLE OF SECONDS