Diagnose and repair Stannah 400 stairlift

Hello there, I bought an used Stannah 400 straight stair lift without a hinge and installed it. Initially the chair would move a little and stop. I could power cycle the stair lift and repeat the limited movement. I measured the voltage on the batteries and one was 13.5 V but the other one was at 11.9V. Thinking I needed a new battery I replaced the lower voltage battery. I may have created a short during the battery swap because I blew the fuse going from the negative terminal on one battery to the positive terminal of the other. I replace the 20Amp fuse and now when I turn the system on, it goes into a continuous beep. LED#6 on the main board is continuously on. LED#4 blinks at regular (fast) intervals. Any cues as to what might be going on or a pointer to a service manual will be greatly appreciated. Best, Sumit