QSC, If I recall correctly, is who Behringer had design and build the EP1500 and EP2500. Now they are produced at Behringer City. I checked the link, but only got the one page. There is also a page with the other channel, and a page with the power supply, and the input jack section. But just try and get the Beefeater to give out that info.
On that schematic, there is a Bias pot VR6. That pot can be adjusted so that there is 80mV across R106. If there is no bias across R106, and either one or both zener diodes D9,D12 are bad, upon replacing the zener diode, the amp works, What other components or voltages should be checked? I thought zener diodes were kind of fragile, especially these glass kind, and excessive heat can be the cause of failure.