The base for CPU to judge bias excitation faults is that the current waveform output by transformer which is originally continuous is interrupted, not continuous.

        The reasons for causing faults in bias excitation are as follows roughly:

1. Faults in rectifier transformer. In rectifier transformer, if there is a group of rectifier bridge arms among the 4 groups damaged, the alarm of bias excitation will be caused. Moreover, the sound of rectifier transformer itself is very noisy. The rectifier  will be easy to burn out in working with faults for a long time.

2. Problems of controller and interface board. The trigger signals of two SCRs are obtained by that the controller outputs two-way signal to interface board, for being amplified by 8050 on interface board and then the signals passes the small pulse isolation transformer. We can observe whether the two LEDs of equipment on interface board are lightened in operation. If more than one of them is not luminous does , then problems may take place on aspects of amplifying audion loop, data line, controller generally; if both of them are luminous, inspect whether the pulse isolation transformer and silicon controlled are damaged or not

3. In major loop, if the capacitance in RC absorption circuit of two anti-parallel connection silicon controlled punctures short circuit, bias excitation phenomenon will also be caused. And problems existing at the same time also include that, when the equipment is electrified  but not operates, and the second voltage is indicated, it is about 15-20KV generally, greatly higher than normal reaction voltage (about 5-10KV). 

4. If the problem still can’t be settled upon the above troubleshooting, please contact the manufacturer for assistance.