Generator high-voltage throttle fault

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Since our company has no prior experience with the DEH systems used in power plant generators, we supplied the steam turbines to Hangzhou Zhongneng for their servo controllers (electro-hydraulic converters), while Shanghai Zhidao was provided with such controllers as well. Initially, due to frequent fluctuations in the high-pressure valve positions, those servo controllers were sent to the manufacturer for repair. This time, after installing these controllers and establishing oil pressure, the high-pressure valve still would not operate. Upon inspection, it was found that the input current signal to the servo controller was 80 mA, and this value did not change regardless of manual adjustments (the DEH control system was provided by Nanjing Keyuan). Both the DEH control functions and valve position control were integrated within the same module; it was determined that there was a fault with the feedback signal for the high-pressure valve’s position (the L1 indicator light was on). After swapping the two position feedback signals, the L1 indicator light goes out. Following the manufacturer’s instructions, a 7# battery was connected to the server’s input, the valve was adjusted to its maximum position, and normal operation was restored after the wiring was reconnected. The problem can be summarized as follows: The module’s output is locked and unable to function due to a fault in the high-gain position feedback. Apply current using a 7# battery to force the server to power on. I asked the manufacturer whether it was possible to add a signal using a signal generator, and they replied that it was not possible ； Since the instrument and control personnel in our unit all have backgrounds in the chemical industry and have no experience with instrument control in power plants, I wonder whether this signal truly cannot be quantified. After checking the module’s specifications, the output range is stated to be –180~180 mA. How do you handle this fault?