My HM4 did the same CHIRP when pushing the On/Off button and it wouldn't come on. I fixed it. It was a 1000uf 25v capacitor that sits right behind the heat synced voltage regulator on the upper left of the circuit board. Unfortunately you have to scrape out the hardened wax they use....I guess it's to keep components from moving. Once I did that I could actually move the capacitor back and forth. It's + lead fell right out of the capacitor. I soldered in another cap from a junk circuit card and the heater works GREAT. Never could get a schematic. My guess is they used cheap capacitors and they probably fail in quit a few units.