Our HP4650 has vertical lines though the print out

Sounds weird that all three are having the same issue.
If it would be a hardware problem, it could be either Toner, Drum or Transfer Roller.
On Vertical lines it could also be the Fuser.
Though it sounds unlikely that all three gets the same defect,
Tried printing an internal page?

archelle man: If this lines are darker, then the problem is in the ribbon. Try with another ribbon and decrease the print darkness.

Roberto Martinez
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The photosensitive drum needs to be cleaned or replaced. If after cleaning it the vertical line continues, the printer may need maintenance.

Needs a new printing ribbon.

I have problem while printing colour photos and I would like to know how to print back to back i.e. even and odd pages

Try printing a configuration page to see if that comes out. If it does then you might have a print driver problem. Also try printiing a test page from the printer properties on that printer.

Turn the printer off then back on or download a new driver from hp web site.

The heads are clogged, probably the #8 head. do a cleaning. if that doesn't work, it may need servicing.

Look really close at the small glass strip. There will be toner embedded in the glass. It will probably be a very thin streak though, so hard to see.

Clean the glass with IsoPropyl Alcohol. Dont use any other solvent. A speck of dust stuck to the glass can give a continuous line in the output

S. Mohan