Does anyone have any service info or a schematic on the G-500 acoustic amp? I have one for repair with a loud hum/buzz independent of the master volume. I did observe ripple on the PS rails- replaced the filter caps- no luck. I have a schematic for the G-600, but it doesn't seem to quite correspond to the G-500. For example, the G-300 and G-600 schematic show Zener diodes in the PS- but I don't see any for the G-500. Been chasing my tail for awhile on this one- any help would be greatly's almost like this amp came from some weird alternate universe and there is no information anywhere on it.