hi Lee
the diode test function is a very basic test for bjt's, sort of a go no go test. it does not test leakage or gain.
also be careful when checking. b, c and b,e diode check, should give you a diode drop (0.5 to 0.7v) reading on each,
but if the transistor is short from c,e it will possibly pass this test.
test from c,e as well, no reading is good.
are both channels of this amp faulty?