Printing problems with Lexmark X5150

The printer only prints the yellow colour and black.
The test print shows in place of the colour bars just yellow, but oddly
each yellow bar stops at different places across the page! The ends of the
yellow lines form a diagonal but obviously as the colours should be the same
right across the page, so the yellow component should continue across the
page.
I have tried many cleaning cycles without improvement. But touching the
print head on some damp paper shows all three colours in equal intensity.
This suggests an electrical problem but I have used a dry cloth to clean the
contacts on the cart and in the printer.

Any thoughts?

Nigel


.