M830BUZ is a popular (due to very low price, usually ~$5) entry level digital multimeter. "BUZ" suffix stands for buzzer. Versions without buzzer are probably not worth buying as price difference is marginal if any. Unit disassembled here is over 12 years old (and still in good shape), branded as UNI-T.
Bubbles on the front sticker started appearing pretty quickly after purchase.
Heart of this multimeter is ICL7106 clone. In this unit chip is glued to additional PCB (branded UNI-T again) that has DIP-40 package size.
Dual operational amplifier (2904) is working as comparator activating buzzer and buzzer sound generator. Whole scheme is easy to find on the internet.
Rotary range switch would be probably critical component for device lifetime. I've saw over a dozen damaged multimeters of this type in RTV service and burnt switch traces (caused probably by accidental overvoltage / range error when servicing equipment) was common problem. Input protection is quite poor in this multimeter. Other possible problems are no auto power-off function (replacement battery costs about 20% of new multimeter) and hard to determine (random) quality of connection leads (mine survived over 5 years though). Of course additional features and high quality leads would not allow to keep price tag, so this have to be expected and acceptable at this price.
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