The Metrohm 665 Dosimat is a microprocessor‑controlled liquid dispensing and titration unit featuring an integrated syringe, automatic stopcock changeover, RS‑232C/USB interfaces, and a digital display for process control. Common failure modes reported include port blockage or improper piston positioning (often “piston up” on Port 2), tubing wear or leaks that trigger error codes, and communication faults with external printers or PCs. For initial troubleshooting check the power supply voltage and current to ensure 100‑240 V/15 VA operation, inspect all inlet/outlet ports for blockages or damaged seals, and review any displayed error codes or log entries via the RS‑232C interface.[oss-gpt-20b]