Bought one of these broken to fix and use testing AC power. I could not find any information about these so I will include what I know.
The unit must have been designed in the1990s based on Firmware 1.01 from 1994.
The unit came as promised not working. There was some battery corrosion in the battery box but nothing major.
The inside is a mix of SMD uPC and through hole on everything else.
There is a battery backup that supplies power to a static RAM. This battery was found to have only 200mV so no way it could provide any backup but the manual mentions the life of the battery is about 11 years so no surprise its dead after 30.
After inspecting the unit and reading the firmware I proceeded to power the unit from a power supply . The meter would turn on the back light and consume about 185mA but the screen would just flash for a moment and show nothing.
My thought was that the micro must be working as the display seems to refresh and disappear.
After some messing around I went for the user manual. It turns out the software starts the screen with no contrast. this can be adjusted by pressing the enter / arrow keys together. That brought the screen back to life.
Mechanically these seem to have issues with the buttons. There was a meter retention ring holding the buttons in place. After years these retention rings just fall out and they seem to also crack the plastic around the buttons.
I designed a plastic button retention unit that fits on the remaining plastic and adds supports that brace against the PCB board.
Now waiting on a battery holder to replace the soldered in 2032 backup battery.
Voltage measures in line with my modern multi meters. Harmonic display is very interesting. Seems there is 5% of harmonic content in my house.
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