This searches the Website not the forum
PYE 693 CHASSIS
The screen lights up two -three minutes after the set is
switched on, but for the next nine -ten minutes the picture is
very blurred. It then becomes sharp. Also, there’s a loud
crack and a flash from the line timebase area during warm
up, when changing channels, or when the brightness is
lowered.
The trouble is undoubtedly in the VDR from which the
focus voltage is obtained. If one end connection has become
loose, you may be able to repair it by bonding with wire. Be
careful though, there’s 25kV on one end!