[GE] VHF Mastr III question

[n griggs]

Gentlemen (and ladies),
I am about to plunge head first into the repair of a VHF Mastr III power amplifier.  This repeater is currently setup as a ham repeater here in Georgia and, recently, started suffering from poor reception problems.  Upon arriving at the site and putting a power meter on the output, It was discovered that the power level was 6 watts and not the full 100 watts that had been set back in March.  We have a complete spare that is going to be put in place and my question is this:  where should I look first before going full bore at troubleshooting this?  Is there a common failure of these amps?  Also, if the finals are toast, is there a good source for them short of contacting GE/Ma-com/Ericsson/who ever they are this week?  RF Parts does not show them.  I have repaired GE, Motorola, Johnson, Aerotron (there's and oldie) as well as a few others so there shouldn't be that much of a problem.  I also have all the LBI's for the current modules.   Any
 assistance is appreciated.
Thanks

Neal KC4YCM