[Amps] help diagnosing a bad 8450a probe ?

[Dan Sawyer]

All,

I have an 8405a with a bad probe. The unit makes it through most of the 
calibration until the noise cancellation step. One board works and comes 
in at less then 5 mv. However one shows a 1V peak to peak distorted sine 
like wave. This probe actually works, however due to the fault it has a 
phase frequency error. This error is of course disaster for a phase meter.

Does anyone have experience in diagnosing these probes?

Does anyone have a lead as to what part to suspect?

Thanks - Dan