Hi Chris,
The only thing I have had is the convergence IC's failing, you replace them with a uprated version Part Number 23135090 (STK392-110T). It's been a while since I worked on one of these but I think you may be able to disconnect the IC's and then switch on, and if the set works (with convergence errors) then the IC's have failed.
One word of warning, if the IC's have failed, you might find it is a long job setting up the convergence after you have changed the IC's! So make sure you allow for that in your quote.
Brian