Ruger P90 wont work double action

[sheephearder]

A friend has a like new P90 that will shoot single action but the trigger will not lift the hammer in double action. If you let the hammer down from full cock it is possible to catch it and lift it with the trigger but the trigger only lifts the hammer so far but will not release it. Does any one have a suggestion or a simple fix, before he sends it back to Ruger? Thanks Bill