HP 8500A Printhead Problem

[RBonz1965]

I purchased brand new print heads, aligned them, cleaned them, and the machine worked briefly. Now, the machine says to replace printhead. I manually cleaned it, but get same message. Help!

[Valsimot]

Each printed has expiration date stored on them ( on an integrated circuit)  it's possible if the expiration date is passed the printer will no longer accept that printhead.  You can check expiration date is stamped on each printhead, and on the box if you still have it.