Today I had one of my Herpstat 4's open so I could clean out dust build up. I do this every 6 months to keep everything running like new. I decided to take a picture and explain how these things work for those who are interested.
Color code:
Red: The 4 Triacs. These are what do the hard work of reducing the power going to each output. Each Triac has a heat sink as they can generate a fair amount of heat.
Orange: The Internal Temperature sensor. This tells the herpstat if it needs to run the internal case fan or not to keep the herpstat from overheating (I've never had mine need to turn on)
Gray: Mechanical relay. This physically cuts power to the thermostat in the case of a thermostat failure (prevents the thermostat from failing in the "on" position)
Blue: This is the speaker for the alarm and beeping while navigating the various menus.
Purple: These 2 chips are the "Brain" of the thermostat
Magenta: Battery (either to keep settings in the case of power failure or for the real time clock. I'm not 100% sure but if I had to guess I would say that it is for the clock)
Yellow: Clock (for night drop functionality)
The build quality on these units is really top notch. Besides a few pins that were slightly overheated during the soldering process this board is spotless. Practically military grade.
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