E - Teardown

Oh man... A 3.3 Ohm resistor... You surely do get a whole lot of 'worth' for your money these days.

No.

A massive voltage drop of 0.8xx volts at about 300 mA. Shocking!

No wonder the buzzer wasn't working properly any more. They should have soldered wires to it instead of using spring contacts. "Planned obsolescence" at work?

The MC145010P is the brains of the circuit.

The MC145010P is the brains of the circuit.

The MC145010P is the brains of the circuit.

With no small particles in the air, the IR beam goes straight into the wall of the housing. The wall is black and absorbs a great deal of the radiation. The little fins might be angled in such a way that the reflected radiation bounces around many times, which further attenuates it. Ideally nothing ever hits the sensor. The main purpose of this construction is to allow smoke-carrying air penetrate the walls, but keep ambient light out. When tiny smoke particles are present in the center of the sensor, they scatter some of the IR light towards the sensor. You hear a very load beep.

I used a bit of abrasive dish-cleaner to remove most of the oxidization. The smoke detector didn't survive dismantling. I need a new one.