REFLECTOR: MT Prop failure mode?

[Bernard Despins]

I have a TIO-540 on a test stand with a 4 blade MT constant speed 
(hydraulic) prop.

It has been running fine, producing 300 hp. Today, it started up normal, 
warmed up, but when it came time to make some horsepower, it just revved 
to 2700 rpm, and wouldn't develop any power, and the manifold pressure 
wouldn't go up.  Thought maybe the turbos were damaged.  They seem 
fine.  The engine is just essentially free-wheeling and over-revving 
with the slightest application of throttle.  It is as if there is no 
load on the engine.

The prop still responds to the pitch control, but it doesn't seem to 
provide much more load even when set to course pitch.

Can anyone point me in the right direction to diagnose this a bit more?

Bernard Despins