The test of the bridge is to measure across each side of it for shorts. STart at one corner and measure resistance to the next corner. Then start at that second corner an measure to the third, etc. Don't want to see shorts. If possible, disconnect the power transformer wires so the transformer winding doesn't interfere with the measurements.
I would be you have some shorted output power transistors.
It would be a lot easier to help if you identified the amplifier.