Tektronix 2445, No EHT , oscillator board 'failed' common faults ?

After many years of use, the scopes failed ..

Everything was fine, then lost the trace....On checking, the 750 mA
fuse on the -15v un-reg line had blowen, turns out the A9 , eht
oscillator board is drawing excess current .not oscillating .. no
signe of anything over heated

... scope powers up fine with A9 board 'out' looks to pass all self
tests

Q are there any 'common' fail's for this board , the power transistor
looks to be giving 'odd' reading's and ive ordered one to replace
it .. are there any other components that are know to 'fail' ?

Tnx

Graham ..