Blinkenlichten II

Once taken, twice removed, I suppose.


By which, I mean to say that it was fairly certain that fixing the broken christmas light timer was possible if all the electrical components were intact. We bought two last winter, and thereby instantly removed the bedtime "Who's going to unplug the lights?" discussion and also the equally awkward "Wow look at the december electric bill!" associated with running the lights 24/7 during visits with family. On at 4:50, off at 11:00 every night.

Then, sometime this summer, one of the timers stopped working. Screen blank. No clicking relay. Zilch. Reset button did nothing. Plug/unplug did nothing. Appeared dead. But of course, I had already opened it and determined that it was almost too bloody simple to die. As long as the ballast capacitor stays in spec, it should work about forever.

 I pried the timer open to see this again:

For reference, the left side PCB with all the components is an AC/DC converter, and an SSR driven by the transistor, which is in turn driven from the blue wire that leads to the right hand PCB, which is the timer microcontroller, the screen, and buttons (not shown). The major components on the timer board are few. On the back, there's a oscillator, a photoresitor ("Dusk"), and a battery (the green shrinkwrap thing). The timer charges from a 1.45 volt line through the red and yellow wires. I think the AC/DC conversion is actually 12 volts (for the relay), and then a seprate resistor drops it further to supply the controller. Though, that leaves the purpose of the big red capacitor unanswered. Regardless, I wasn't there to diagram circuits.

The controller battery was a) charging and b) charged. That narrowed the problem down to the controller and the screen. I removed the control board and noticed that one of the fingers that holds the screen to the timer PCB was loose. LCDs often use a silicon surface contact. I removed the screen and found the controller CPU underneath, along with test, reset, ISP and ground pads. I grounded the reset pad for 5 seconds cleaned the LCD contacts,and pressed it back together until it snapped. The screen started working, blinking time like a VCR.

Rock on green box, rock on.