It could be one of the Analog to Digital (A/D) converter IC chips on the processor board has gone bad. Its a board level repair that would have to be sent to Drager for repair. Unfortunately, this machine is end of life, end of service and Drager no longer offers any parts or service for it.
You could try buying a used machine and pulling the board out of it for a replacement.
Brent SilviusAnesthesia TechnicianBiomedical Sales and ServicesMercuryMed.com