Apple IIgs ROM 03 system bad error

I have two ROM 03 Apple IIgs systems that give intermittent errors "SYSTEM BAD 06010000" From what I looked up it seems to be an issue with the built in SERIAL IC on the main board.Is that correct or is the issue something else? My concerns are system stability. IF I disable the modem port in the control panel and add a super serial card will the system work as intended sans the on-board serial components? Would that create a functioning machine? Two ROM 03 machines thrown away would be a huge waste, I am trying to get some use out of them. I guess they had inherent issues with the serial chips.Would appreciate the feedback.