DM504A

Manuals – Specifications – Links – Pictures

The Tektronix DM504A is an 4½ digit autoranging digital multimeter plug-in for the TM500 system.

Key Specifications

DC Voltage	200 mV to 1000 V in decade steps, ±0.05%; Input resistance 10 MΩ (200 kΩ in 0.2 and 2 V ranges if Vin > 12 V)
AC Voltage	200 mV to 500 V in decade steps, ±0.6%; Input resistance 10 MΩ // 100 pF
DC current	200 μA to 2 A in decade steps, ±0.1%;
AC current	200 μA to 2 A in decade steps, ±0.6%;
Resistance	200 Ω to 20  MΩ in decade steps, 0.05% (0.1% in 2 and 20 MΩ ranges
Temperature	−62 °C to +230°C with P6602 2-wire PT-100 probe
Display	4½ digits, red LED, 2/s update rate
Features	Modes: DC Volts / mA, AC Volts/ mA (True RMS), Ohms, and Temperature Diode Test and Audible Continuity (Beeper) Modes

Links

• DM504A @ barrytech.com
• DM504A repair by VintageTEK Museum @ YouTube

Documents Referencing DM504A

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Internals

The DM504A has no rear interface I/O. The entire circuit is supplied from a +12/−12/+5 V floating power supply that uses a small mains-frequency transformer fed by one of the mainframe's 25 V_AC windings.

The circuit is based on an 80C31 microcontroller with a Texas Instruments TL500C integrating A/D front-end and a 1N827 temperature-compensated zener reference. The DM504A is software-calibrated, storing cal constants in a 93C46 EEPROM. Calibration is triggered by pressing Up and Down buttons simultaneously while the internal cal jumper is in the "enabled" position.

Pictures

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  DM504A

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  DM504A

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  DM504A LH Interior with HV shield in place

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  DM504A RH Interior with HV shield in place

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  DM504A LH Interior with HV shield removed

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  DM504A RH Interior with HV shield removed

Components

Some Parts Used in the DM504A

Part	Part Number(s)	Class	Description	Used in
AD737	156-3506-00	Monolithic integrated circuit	RMS/DC converter	DM504A
Intel 8031		Monolithic integrated circuit	8-bit microcontroller	11A33 • 571 • DM504A • DM511 • DM5110