crown XS900 amp problem

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i'm repairing a Crown XS900 amp, and the customer tells me that there's an occasional subsonic oscillation that smokes speakers. i have previously worked on this amp, and found the front panel PCB worked loose of it's connector to the main board. this time i found that most of the transistor screws were not really tight. does anybody A> have any experience with this problem (subsonic oscillation) or B> have a schematic for this beast?

bias and offset are ok (assuming that 20ma per transistor is correct, as it's about normal for 99% of the amps on the market)
 
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