12th January
2014
written by Todd Harrison

This vintage Scooby-Doo alarm clock has been in the family for many years but the plastics had degraded causing the internal supports for the buttons and displayed to break. My original goal was to simply replace the broken plastic supports by adding some custom internal brackets, unfortunately the alarm also did not work which turned into a lengthy electronics repair.

<video of repair>


Update:
The resistor substitution box is George Graves’s design and is detailed on his site “Digital Underpants“:

CLICK to read more and see photos —>:

Plastics are easy enough to fix but the main chip-onboard which controls the car honking alarm sound was shorted internally. Fortunately when reviewing the data sheets for the clock chip I discovered the clock chip had the ability to directly output a standard beeping alarm sound to a speaker. The standard beeping alarm sound was an acceptable substitute alarm sound; however, we will greatly miss the car honking alarm sound that was implemented within the chip-onboard circuitry.

This was a bit of a hack repair because I had to cut some PCB traces and change the functionality of the existing circuitry in order to implement the standard beeping alarm sound function of the clock chip. You can follow along with my evaluation and repair in the video and view the photos below.

If you have questions please submit them on the YouTube channel as I have had to disable comments in my blog due to too much spam.

 

Photo Gallery

CLICK PHOTO for gallery view and click a SECOND time for hi-resolution image. Click thumbnails on lower right and lower left of gallery to navigate gallery photos.

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