I have a GE channel master (21C2478). I've recapped the whole thing and sound comes through but there is no picture (although there is a flat line going horizontally across if you adjust the brightness to a certain point

Not familiar with that exact model, but see if there's a service switch on the back of the set......

Was it like that before ?
If not the service switch ( not all sets have one, B&W's dont)
its a vertical problem. Post a few chassis pictures & maybe
things will come to mind.

73 Zeno:smoke:

Here are some pictures of the tv

Vertical deflection failure. Check the vertical stage tube(s), resistors, vertical output transformer and replace parts out of tolerance. Also may want to confirm B+/B++ rails to the vertical are working and within %30 tolerance of rated values. Also check your cap work in the vertical for mistakes.

Can you make that line bright? If you can, good, but don't let it stay bright for more than a second or you will burn that line permanently into the phosphor. If you can't make it bright HV is low, CRT is not being driven properly or CRT is bad.

Some capacitors look to be replaced, make sure the old ones are snipped out. Also make sure new cap value is correct on the yoke, and remove the white tubular.
Is that 15M5 or M6 stamped below the 5U4? I may have a schematic for this set so you can do a check.