Link — Protek Service Manual

| Symptom | Likely Cause | Service Manual Section | | :--- | :--- | :--- | | Oscilloscope trace won’t focus | High voltage supply (CRT) | “Z-Axis & HV Board” schematic | | Multimeter reads “OL” on all ranges | Blown input fuse or protection PTC | “Input Protection” and parts list | | Function generator no output | Output amplifier stage dead | “Output Attenuator and Amp” schematic | | Power supply voltage jumps when load changes | Reference voltage drift or worn potentiometer | “Calibration - Voltage Setting” section | | Display shows garbled characters | Faulty RAM or display driver IC | “Microprocessor / Display” block diagram |

Documentation for the 3000 series (e.g., 3003B ) covers constant voltage/current operation and internal fuse locations. Protek Service Manual