The easiest way to find out what's wrong is to unplug the unit and short the triac with a test clip. Plug the Carver into a variac, 2A model is fine. Bring the AC up to say 20V while watching the current meter on your variac (add one if there isn't one). At this level, you can check for high ripple on the supplies or rail voltage on the outputs. If you draw current, bring the voltage up a bit until you have 1/2 ~ 1 A of current. Measure across the emitter resistors to find the offending channel. Current draw right away normally means shorted rectifier(s) or capacitor. Never attempt to bring the unit up past about 60% voltage this way. The current draw will be heavy and if you continue, you may overvoltage most of the circuits. You will overvoltage everything if you manage to get the AC up to normal levels. Make absolutely sure you remove the short across the triac whenever you leave the unit (so you don't forget).
If you get a chance to bench one, the operation is interesting. Dual trace 'scope and you can watch the supplies against the output signal. The power supply is a standard triac regulated circuit using a mag coil. Effective, but doesn't like generators or high impedance AC lines.