The document explains the calculator’s construction, electronic operation, repair procedures, and performance testing. Mechanical construction: The calculator consists of five main assemblies: the cover, keyboard, printed circuit board, power assembly, and base. The manual provides illustrated instructions for dismantling and reassembling these units, including replacing keys, switches, connectors, and the display tube. Keyboard: Each key uses a magnet and a reed switch to register a press. The manual explains their alignment, adjustment, and replacement, and identifies causes of unreliable key operation. Electronics and display: Two main integrated circuits, T3125 and T3147, perform calculations and control the machine. TM4355P driver circuits operate the E6516 fluorescent display, which shows twelve numerical digits together with minus and overflow indications. Troubleshooting: Diagnostic guidance covers power failures, a blank or incomplete display, incorrect segments, missing decimal points, faulty keyboard input, calculation errors, and problems with automatic clearing at startup. Checks focus on supply voltages, timing signals, connections, switches, and integrated circuits. Testing and reference material: Detailed calculation sequences and expected results allow technicians to verify operation after repair. The document also includes a screw-location list, circuit-board layout, and a complete electrical schematic. The manual’s main purpose is to help technicians locate faults, replace defective components, and confirm that the calculator works correctly after servicing.