Repair and reverse-engineering notes for a Bender UNIMET® 1000 ST electrical safety tester for medical devices (IEC 62353 / DIN VDE 0751, built ~1995). Much of it also applies to the UNIMET 1100 ST.

What you will find here

• Boot troubleshooting — Using defaults for system configuration and a looping Diskette error: causes and the way into the BIOS setup
• RS-232 command set — interface parameters (9600 baud, 7E2, null modem), protocol, 427 test steps and 493 commands of the UNIMET 1000/1100 ST
• I²C relay matrix — PCF8574 port expanders at 0x24/0x25 driving the relay board (partially mapped)
• Connector pinouts of the CPU module (Chips & Technologies F8680 “PC/CHIP”, XT class, 14 MHz) and the display
• BIOS dump analysis of the NM27C010 EPROM, version V: 0.91

The short story

The unit arrived not booting. The boot failure was fully explained — a stuck front-panel key and a missing PCMCIA flash card that held MS-DOS 5.0 and UNIMET.EXE. But the measurement card was missing too: the analog measuring chain and the mains switching sat on it, and it is a Bender-specific part. The unit had also been deliberately converted into a display terminal for a Bender RS-485 bus before it was sold. The project was closed on 2026-07-31 without restoring the device.

Documents (German)

Document	Content
Status & final interpretation	start here
Findings	fault diagnosis, pitfalls, search for the OS image
BIOS analysis	setup structure, boot messages
RS-232 reference	full command set and test steps
Relay matrix	I²C control and bit assignment
Connectors	pinouts of all CPU-module connectors
Measurement hardware	specs, reconstructed relay topology
Incoming inspection	first power-up checklist
Transformer	characterisation of BG160 805 Q3995
Sources	where to get the manufacturer manuals

Manufacturer manuals, firmware and software are not published here (copyright).

Source and photos: github.com/feiglein74/bender-unimet-1000st · License: CC BY-SA 4.0 for own content, see LICENSE.