DM502A

Manuals – Specifications – Links – Pictures

The Tektronix DM502A is a 3½ digit TRMS digital multimeter plug-in for the TM500 system.

It superseded the DM502 predecessor in 1979.

Compared to the DM502, the DM502A adds autoranging, a True RMS converter, and offset circuits to read dB directly in all ranges. The temperature input is for a PT-100 temperature probe (P6601).

An "Option 2" instrument deletes the temperature measurement function, P6601 temperature probe, and all internal circuits associated with this function.

The rear interface of DM502A is limited compared to the DM502 in that it has no current input and no digital output, the latter having been obsoleted by TM5000 GPIB based instruments.

The 2 kΩ measurement range (+HI in DM502A) can be used for diode testing, since a current source of 1 mA is active and the reading corresponds to the (forward) voltage drop of the diode in Volts. The voltage can rise to a maximum of 10 Volts. A second voltmeter is needed to measure the voltage if 2 V are exceeded.

The DM502A has an Int/Ext switch that allows a voltage input via the rear interface to be selected.

Key Specifications

Voltage ranges	200 mV to 200 V in decade steps; 1 kV (DC) / 500 V (AC) top range
Input impedance	10 MΩ
Current ranges	200 μA to 2 A in decade steps
Resistance ranges	200 Ω to 20 MΩ in decade steps

Options

Option 02 deletes P6601 temperature probe and capability.

Links

• Tektronix DM502A The final Restoration by Zenwizard Studios @ YouTube
• Tektronix DM502A Lab Check In and Calibration by Zenwizard Studios @ YouTube
• DM502A Autoranging DMM, video by by IMSAI Guy @ YouTube: Part 1 / Part 2

Documents referencing DM502A

Prices

DM502A Year Catalog price In 2026 dollars 1980 $520 ~$2,100 1982 $550 ~$1,900 1984 $650 ~$2,100 1988 $900 ~$2,500

DM502A Opt.02 Year Catalog price In 2026 dollars 1980 $395 ~$1,600 1982 $425 ~$1,500 1984 $550 ~$1,800 1988 $820 ~$2,300

P6601 Year Catalog price In 2026 dollars 1980 $145 ~$590 1982 $180 ~$620 1984 $210 ~$670

Internals

The DM502A circuit is built around a Siliconix LD110/111A DMM chipset. The entire circuit is supplied from one of the mainframe's 25 V_AC windings through a main-frequency isolation transformer with a 25 V primary winding and 7815/7915/7805 regulators. The 25 V_AC input is the only mainframe connection, so the DM502A could easily be used outside a TM500 mainframe as well.

Pictures

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  DM502A right internal

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  DM502A rear interface

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Components

Some Parts Used in the DM502A