Overview
The DM 5010 was designed as a modular, rackโmountable multimeter module for Tektronixโs TM5000 series mainframes. It combines a 4ยฝโdigit display resolution with a microprocessorโbased front end and keypad control, letting users run measurements locally or automate them over IEEEโ488/GPIB for test systems and production environments.
Key Specifications
- Resolution: 4ยฝ digits with autoranging operation for convenience and speed.
- Voltage ranges: 200 mV to 2000 V in decade steps (top range limits apply for DC/AC).
- Resistance ranges: 200 ฮฉ to 20 Mฮฉ in decade steps.
- True RMS measurement: Supports true RMS AC or AC+DC conversion for accurate AC readings on nonโsine signals.
- Additional tests: Builtโin diode test and support for current measurement via external shunt and scaling. These core specs make the DM5010 versatile for both lowโlevel precision work and higherโvoltage.
I have two Tektronix DM 5010 units that require restoration. This post describes the start of that process.
Both units were operation, but both threw Error 351 (calibration constants lost). The D5010’s originally had a NiCd memory backup battery which had long since gone flat and (possibly) corroded the A4 CPU board.
The original NiCd battery comprised two 1.2v cells in series:
After removing the old batteries and cleaning the boards of corrosion, I replaced the NiCd battery with a long-life Lithium battery:
I added a diode in series with the lithium battery to prevent it from being charged by the original circuitry. The diode allows the lithium battery to supply a small current to the memory chip.
Several aluminum electrolytic capacitors showed high ESR, so I decided to replace all of them:
The circuit cards were reinstalled as follows:
Both of the DM 5010 units were repaired and reassembled as described above. With the new lithium memory battery, the calibration will be held for many years before requiring battery replacement.
The basic functions of each DM5010 were checked and found to be OK, but out of calibration. That process will be documented in Part 2 of this series.