How to take apart Voltcraft/Metex 3650B

[mqsaharan]

Hi Erik,
Hopefully, someone who has this meter or has the better understanding of its schematic will chime in. My reply may not be particularly helpful.

ICL 8069, if it is present in the meter is the voltage reference IC. It is not used for low battery warning. As per schematic in reply #7, it is ZD1 and its output to ICL7106 is marked as R.

The following are my guesses which may be completely wrong.
The *whole display is not directly driven by ICL7106 but in conjunction with RA1-RA4, which is the METEX IC with a clock crystal on a daughter board in the picture in reply #11.
I guess the IC4 in the schematic is generating the low battery signal but I am not sure. My guess is based on the assumption that this IC is feeding signal to the display chip (RA1-RA4).

Edit: * correction. Also, I am not adding further explanation here in order to bump it and in the hope that someone might give better idea to solve your problem with this meter.

[mqsaharan]

A bit more explanation in the hope it might be useful for you to solve your problem. After looking at the schematic again, I'm sure the digits and negative sign " - 1 8 8 8 " are being driven by ICL7106 because it contains both A/D and display driver. But the rest of the segments including bar graph, low battery icon and any other features on the display are being driven by the microprocessor/CPU/Metex IC.
The low battery signal on ICL7106 based meters is external to this chip because it does not have any circuitry onboard for this function. It is usually implemented by using the external circuitry and the Test signal from pin 37 of the chip. On the schematic in reply #7, it goes straight to IC4. This is all a guess because this signal can also be used as a power supply for some other IC in the meter. The schematic is incomplete and I don't have this meter so it is difficult to suggest something with confidence.

[j-man]

Hi. I hope you already solved your issue: in case you don't, let me know if I can help you measuring and checking my own Metex (that is powered by an external 9v power supply, BTW)