Monday, September 24, 2018

Repairing a Scrabble Timer

One of my teachers has a Scrabble set that she purchased at a garage sale. It's a 50th Anniversary Edition which came with fancier pieces and board, a dictionary, and a timer. The timer did not work. I tried to help by replacing the single AAA battery, but that didn't fix it.
Scrabble timer (photo from eBay)


The old AAA battery was very corroded, especially at the negative end (because it expired 18 years ago!). The negative terminal in the battery compartment was also extremely corroded. I took the timer home for further troubleshooting. Once I opened the timer, I could see that the negative wire inside was corroded off, and the PCB was damaged around the button.
timer battery and spring terminal (stretched during removal)

Negative end of the timer battery

My mom's digital kitchen scale had the same problem with the wire corroding off, and I was able to fix it by just replacing the wire. For the timer repair, I had to replace both the negative wire and terminal spring, using parts I salvaged from other things I took apart.
The corrosion on the timer continued onto the circuit board. First, I tested to see if the chip was still functional by connecting a AA battery to the solder joints on the circuit board. I heard a beep, which meant the chip was getting power, so I decided to continue the repair attempt. I cleaned the switch area with alcohol, but the damage was too severe. It's the worst corrosion I've ever seen.
Example of a corroded circuit board- photo by Brabus on eevblog.com 

The screen display worked, but the button did not. So next, I cleaned around the pcb button area. It still didn't work. I replaced the rubber dome part of the button with conductive foam shielding from a satellite dish. Then it worked, although the feel of the button was different.  I discovered that it is a 3 minute timer- perfect for timing ramen noodles. 😋
Conductive foam

Conductive foam

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