Hp 3456a manual: comprehensive guide to the digital voltmeter

The Hewlett Packard 3456A is a 6 ½ digit voltmeter with AC, DC, Ohms, and math functions. It was built in early 1983 and sold for around $3,700. Despite being an older design, it offers several advantages over newer models, including an easier-to-read display, no calibration loss due to a dead memory battery, decade ranges, and a lower noise front end.

Content Index

Features and Specifications

The HP 3456A has a resolution of 100 nV on the 0.1VDC range and 1 mV on the 1,000.0 VDC range. The AC voltage range is from 1 uV to 1,000 volts, and the resistance range is from 100 µΩ to 1 GΩ with 2 or 4 wire ohms connections. It uses an integrating analog-to-digital (A-to-D) converter using the Multi-Slope II technique, which was developed specifically for this model.

The voltmeter measures 175 long by 175 wide by 5" high and weighs approximately [weight] pounds. It features a front LED display that provides clear and accurate readings.

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Restoration and Calibration

If you have acquired a used Hewlett Packard 3456A, it is important to perform a thorough inspection upon arrival. Check for any signs of damage or corrosion, especially around the power inlet area. Clean any residue or corrosion using mild cleaner and a nylon brush. Replace any damaged screws or components as needed.

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Before powering on the unit, remove the bottom panels to check the power supply voltages. Ensure that all voltages are within specifications and that there is low AC ripple present. Consider replacing the electrolytic capacitors, even if they appear to be in good condition, as they are 38 years old and may deteriorate over time.

After powering on the unit, run through all the performance checks and calibrate the meter as necessary. The calibration process involves adjusting multi-turn potentiometers located under the front terminal panel. Refer to the manual for detailed instructions on calibrating the meter.

Additional Modifications

If you want to improve the performance of your HP 3456A, you can consider making some additional modifications. One such modification is better insulating the LM399 precision shunt reference on the A25 reference board. This can be done using insulating sheets such as roVa Flex Plus Aerogel Insulation and Aspen Aerogel SPACELOFT™ mat.

Another recommended modification is replacing all the electrolytic capacitors throughout the unit. While you don't need to replace the ceramic, film, mica, or hermetically sealed tantalum capacitors, it is important to replace the electrolytic capacitors for optimal performance. This includes the 4,000 uF at 15V capacitor (C5) on the A10 power supply board.

If you encounter difficulties finding a replacement capacitor with the same pin configuration as C5, you can create your own C5 adapter board using four Nichicon 1,200 uF 25VDC capacitors. This will provide a total capacitance of 4,800 uF at 25 volts and improve the impedance and cooling of the capacitor assembly.

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Additionally, consider replacing the Corcom AC power line filter module with a new Kemet GL-2030F unit. This is important for safety reasons as the module contains X and/or Y safety capacitors that should be replaced periodically.

Usage and Functionality

The Hewlett Packard 3456A features various function selection buttons, including DCV, ACV, ACV+DCV, 2-Wire Ohms, and 4-Wire Ohms. The shift button allows for additional functions such as DCV/DCV Ratio, ACV/DCV Ratio, ACV+DCV/DCV Ratio, 2-Wire O.C. Ohms, and 4-Wire O.C. Ohms.

The numbered keyboard section is used for storing numbers into registers and selecting math operations. Some of the math operations available include % Error, Scale, Pass/Fail, dB, dBm, Null, Thermistor, and Statistics.

The HP 3456A also features boards such as A20, A4, A30, and A40, each serving different purposes within the voltmeter. These boards contain various components, including Fineline resistor network modules, PTFE insulators, and capacitors.

The Hewlett Packard 3456A is a reliable and accurate digital voltmeter with a range of useful features. By performing proper restoration and calibration, as well as implementing recommended modifications, you can ensure optimal performance and longevity of your HP 3456A. Whether you are a professional in need of precise measurements or an electronics enthusiast looking to expand your toolset, the HP 3456A is a valuable addition to any lab or workshop.

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