[ICOM] PW-1 What does this mean?

[Tony Visco]

Fellow Hams,
The ole PW-1 seems to have come up with another problem.  Tonight when
operating on any band the Amp/Protect circuit activates rendering the linear
useless each time I attempt to use it.

The Auto lamp blinks which according to the manual on page 14 indicates that
"The Power Level of the 4 PA unites becomes unbalanced."
OK - but everything was working just fine yesterday now its not today?

How would the PA units have become unbalanced and what measures need to be
taken to correct this issue.  

I'm using an Icom 746pro as my primary exciter.

Thanks in advance for the divine guidance.

Tony W3EW