I have a problem with my TV, occasionally the picture disappears down to a thin blue line across the centre of the screen, then eventually it rights itself.

I have been told it may be a problem with the Y-scan, but what is the Y-scan??

JeffM, October 2008

Seems your tv has a Frame Time Base fault probably due to bad solder joints.
Best take it to a qualified repairer and refrain from turning it on until it is fixed to prevent the fault getting serious.

xyzbird, October 2008

X and Y axis as in drawing a graph.

On a raster TV; where the "spot" flys across row after row to build up the picture, the Y axis circuit determines where the row is positioned in the vertical axis. You've got plenty of action in the X axis because there's a line going across but not much happening in the Y axis.

Y-Scan is the gradual change in height for each successive X-Scan across the screen. - Leastways that's what I learnt in the 1960s...

Peccavi, October 2008