HP Color Jet 5550dn Will not print yellow even with a new cartridge

[MRMeyers]

I have two of these HP Color Jet 5550dn printers, one will not print yellow color at all, have swapped the toner cartridge between printers all cartridge work fine in the second printer and both display the same toner level in the cartridges.  it would seam as if it is something to do with the driver board but I would like to find out how to confirm the problem and not just guess at it. can any one provide some additional diagnoses information. Thank you. 

[Valsimot]

Swap belts between two printers for testing purposes.

[MRMeyers]

Swapped the entire belt assembly between the two printers and the same printer still will not print yellow so it must be something in the electronics I think but what?

[Valsimot]

Sstep check contacts of high voltage for yellow toner, compare with contacts of different color for misalignment, damage or mech. failure. The contacts are on the right side of the printer when the toner is removed. The toner has copper contacts that aligns with spring contact inside the printer.