HP 34401A 34401-90012 Multimeter Service Guide Edition 3 June 1992

HP 34401A 34401-90012 Multimeter Service Guide Edition 3 June 1992

This is the original Hewlett-Packard service guide for the HP 34401A 6.5-digit digital multimeter, publication number 34401-90012, Edition 3, printed June 1992. It is the primary technical reference for servicing, calibrating, and repairing the 34401A — covering everything from specifications and theory of operation through full schematics and a complete replaceable-parts list.

Specifications & What's Included

• Publication Part Number: 34401-90012
• Microfiche Part Number: 34401-99012
• Edition: 3
• Print Date: June 1992
• For Instrument: HP 34401A 6.5-Digit Digital Multimeter
• Format: Spiral-bound printed manual
• Language: English
• Chapter 1 — Specifications: DC, AC, frequency/period characteristics; interpreting specs; configuring for highest accuracy
• Chapter 2 — Quick Start: preparing the multimeter, measuring voltage, resistance, current, frequency, continuity, diodes, dBm, rack mounting
• Chapter 3 — Menu Tutorial: front-panel menu reference and tutorial examples
• Chapter 4 — Calibration Procedures: HP calibration services, performance verification tests, zero offset/gain verification, AC signal filter calibration, error messages
• Chapter 5 — Theory of Operation: block diagram, front/rear selection, function switching, DC amplifier, ohms current source, A-to-D converter, floating and earth-referenced logic, power supplies, front panel
• Chapter 6 — Service: operating checklist, types of service, ESD precautions, surface mount repair, fuse replacement, pass/fail output signals, troubleshooting hints, self-test procedures
• Chapter 7 — Replaceable Parts: backdating and part changes, main assembly (34401-66501), display assembly (34401-66502), mainframe (HP-3401A)
• Chapter 8 — Backdating: procedures for back issues of this manual
• Chapter 9 — Schematics: mechanical disassembly, component locator diagrams (main board and front panel), HP 34401A block diagram, front/rear selection, function switching, DC amplifier, ohms, A/D converter, floating logic, earth-referenced logic, power supplies, front-panel display schematics; includes fold-out power supplies schematic sheet (34401-66S01)

Applications

The HP 34401A is one of the most widely used 6.5-digit bench multimeters ever produced, introduced by Hewlett-Packard in the early 1990s and carried forward under Agilent and later Keysight branding. It measures DC and AC voltage and current, resistance, frequency, period, continuity, and diode characteristics, and communicates over HP-IB (IEEE-488) and RS-232. This service guide is the essential reference for technicians performing in-house calibration, troubleshooting, board-level repair, or component-level service on the 34401A. It remains actively used today because the 34401A continues to be a standard bench instrument in electronics labs, calibration labs, production test environments, and educational settings worldwide. The June 1992 Edition 3 print covers the full production run of the instrument and is the version most commonly referenced for calibration procedures and schematics.