THM500

Tektronix THM560

DMM with scope features

Produced from (?) to (?)

Manuals

Instruction Manual 070-8840-01 (PDF)
Instruction Manual 070-8840-02 (PDF)

Other

THM500 FW2.0 Changelog (PDF)
THM500 Service Announcement (PDF)
THM500 Service Introduction Plan (Inc. parts list) (PDF)

A605, A621, A622 current probes

Tekmeter Product Brochure (PDF)

(All manuals in PDF format and OCRed unless noted otherwise)

Manuals – Specifications – Links – Pictures

The Tektronix THM550 / THM560 / THM565 "TekMeter" are digital multimeters with some oscilloscope features.

Key Specifications

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These instruments are capable of running on six alkaline AA batteries for 4.5 hours. The display is a 256×128 pixel monochrome LCD.
The DMM section is a 3¾ digit (4000 counts) true RMS meter. The scope has 5 MHz bandwidth and 25 MS/s, 8 bit, 256 samples resolution.

The 550 has one scope channel. The 560 and 565 have two channels.
The 565 has an electroluminescent backlight and a real-time clock.

There was also THM57x series instruments commonly sold under the brand 'Mac Tools' as the ET2020 'Quick Scope Plus' that was essentially a rebranded THM565 that had an automotive specific firmware installed.

The case of this instrument was also used for the 'Cablescout TV90' and 'Telscout TS90' TDR meters sold by Tempo, Greenlee etc. in both black and grey variants. So this can provide a source of spare parts.

Software

THM500 Firmware Loader Utility Disk 063-1815-01 (ZIP) (Including firmware v2.00 and step-by-step adjustment instructions.)

Optional Accessories

TXMDXPB - Deluxe Probe Set
THM5BAT - Battery Pack
THM5CHG - Battery Charger
THMCOM1 - Communications Adapter (RS-232)
THM5AC - Power Adapter
THM5HCA - Transport Case
THM5SCA - Soft Case/Hands-Free Pouch
A605, A621, and A622 - Current Probes
REP4100 - Service Assurance — Repair Protection
CAL4100 - Service Assurance — Calibration Services

Included Accessories

012-1447-xx - Standard Probe Set
200-4101-xx - Battery Holder With Screws
070-8840-xx - Instruction Manual
070-8951-xx - Performance Verification Manual

Links

EEVBlog Forum Threads:
- EEVBlog Forum thread on THM500 series

Internals

This instrument was not user adjustable, having to be sent back to a Tektronix service center for adjustment and firmware update.
The adjustment process is similar to the THS-series_oscilloscopes, but it requires a 'Firmware Loading Fixture', part number 067-1446-99. This fixture was also required to update firmware.
The fixture was essentially a 7.5 VDC linear supply to power the instrument, a second 12 VDC linear supply to enable programming mode, and an isolated RS232 interface to allow the sending and receiving of commands and firmware data from a PC.

Using the information and software above, a Firmware Loading Fixture can be constructed and firmware updated and adjustment performed. The fixture can be as simple as a bench power supply and a serial to USB adapter etc.

A strange quirk in these units is that calibration can only be performed 10 times, at which point a counter runs out and no further adjustment can be performed until the firmware is re-uploaded to completely reset the instrument. After the firmware upload, the instrument can be calibrated another 10 times before another firmware reset is required. This process can be repeated indefinitely.

There was also a problem with loose banana jacks. When an instrument was returned to a service center, a special tool was used to hang a weight from the banana jack to check if it was too loose. If any banana jacks pulled loose, the rear case assembly (including jacks) was replaced with an updated part.

These instruments MUST have all electrolytic capacitors replaced. They have a problem with leakage, and the main power supply filter capacitors cause the two LTC1174CS8 voltage regulator chips to fail due to excessive ripple and the current leakage paths across the PCB caused by the leaked electrolyte.