I can't read diagrams much but I don't see one. If you can't see one when you open it up, there probably isn't one..they would hardly be hidden anywhere, at the most in a casing in the lead like in car stereos etc.
Check the tweeter with a weak/almost dead battery, like a used up 9V, is it completely silent? DO NOT use a fresh 9V it's too much.
Otherwise Duffy pretty much explained all there is to know and do :-)
Dee
"When life's a biatch, be a horny dog"
Amps: Marshall JVM 410H w/ Plexi Cap mod, Choke Mod & Negative Feedback Removal mod, 4x12", Behringer GMX110, Amplitube 3/StealthPedal
Half a dozen custom built/bastardized guitars all with EMG's, mostly 85's, Ibanez Artwood acoustic & Yamaha SGR bass, Epiphone Prophecy SG, Vox Wah, Pitchblack tuner plus assorted pedals, rack gear etc. for home studio use.