Mercury 400 LB Amplifier Failure

Problem reported: There is the 1H signal but no 13C and 31P signal.. Check the puse from amplifier, No output, check the input to the amplifier, there is a pulse. Checked power supply for the amplifier, +28VDC are OK. Part number: 01970011 125Watts 20 - 162Mhz. Varian 993935. You need a special cable to check the input signal.