I opened up an Ecobee 3 that was given to me by my friend that is the HVAC professional. He took it off a job where it was configured to operate a Heat Pump when the AC became "Stuck on" for something like 13 hours in Cool mode during the Summer. After he gave it to me I was able to add it to my account and review the Home IQ System data and I could see where the unit apparently became "Stuck On".



I put this in another property of mine to see how the unit responded. For Cooling on a HVAC system with a standard single stage cooling and natural gas furance, the unit worked fine for the Summer while the AC was on. Fall came and I needed to change over to Heat. Well the thermostat and display showed that the heat was commanding on, however, the furnace was never turned on by the thermostat. I could run the Fan no problem, just no heat. Well it appears that the FET/JFET/MOSFET for the Heat must have been damaged/blown out when the problem happened on the original installation??

While I have not tried to "spoof" the thermostat to attempt to run/configure the 2nd stage W2 terminal to run the heat, which I may have been able to do, I decided to take the unit apart and inspect it to see if there might be a way to repair it or replace the bad FET/JFET/MOSFET. While I have not put a lot of time and effort into this thermostat so far, I might consider swapping one of the other FET/JFET/MOSFET from say the Humidier/Dehumidifier section to get this unit working. If I have time, I may mess aroud with it some more, but this assumes I can find time. BTW, I do have pretty good soldering skills and equipment and have reworked and build SMD boards in the past.

Anyway, here are pictures I took of the insides of the unit. Note there is a backup battery for configuration and I identified a number of Opto Isolator components, not sure what they are for, but I also found 9 semiconductors labels T1-T9 which I assume are the FET/JFET/MOSFET's that are the output drivers for things like the Fan, A/C, Heat, Reversing Valve and Humidifier/Dehumidifier??

Again, sharing so this might help others and maybe someone has spent more time inside one of these thermostats and can share of comment on what they have found.

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