This is better! There's a reason traditional core 'n' coil transformers are used in stuff like this. Using an old fashioned transformer gives better electrical separation and gets rid of the stressed out low-ESR capacitors.

I didn't originally intent to go quite so deep with the schematic in this, but it turned out to be quite interesting inside. Note the custom badged relays, which I would guess are of a better quality than the Chongle clone ones. The thermistor is the classic 10K type (10,000 ohms at 25C), but injection moulded in a plastic case like some of the industrial ones I recall from my Hussmann days.

This unit is notable for offering a choice of celcius or farenheit display, but changing that option will reset all the existing settings.
The allowance of circuitry positions for an RS485 network is intriguing. Especially as the address setting facility is already in the programming menu. I'll guess it's for remote monitoring of multiple cases. There are three pads for a connector, but only the RS485 data lines are connected. For the screen/reference the thermistors 0V connection would have to be used. So this may be a work in progress.

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