Update:
Today I decided to take a voltmeter to poke around the thermostat to see if there's actually a power supply problem.
Found a manual online and identified the color of the +/- 12VDC connections on the circuit board. There's 13+V across the blue & red wires. Took the circuit board out from the casing to see if there's anything obvious like loose connections or pinched wires. No luck. I reassembled everything together and prepared to throw in the towel. I thought to myself since I only took out the onboard fuse & visually inspected it last time. Why don't I check it's continuity with the ohmmeter meter and it's not blown.
However, when I reinserted the fuse back in, miracle happened. The digital display works again. Only explanation I can think of is it reset itself after power off long enough.
