This is more of a hack than a repair which is a good reason for me to feature my Scooby-Doo alarm clock repair. I started out trying to simply fix some broken hardware mounts that hold the display and button mechanism within the alarm clock that looks like the Scooby-Doo Mystery Van. During testing I noticed the display was very dim suggesting an unusual current load or other malfunction, plus the alarm was not functional.
One of the coolest features of the alarm was that it made a car honking noise when the alarm was activated. Unfortunately, it turned out that the chip-onboard which produced the honking sound was shorted internally causing some transistor overheating and the dim display. It was impossible to restore functionality of the custom chip-onboard, but lucky for me the data sheets for the LM8560 clock chip revealed that it could directly output a standard alarm beeping sound to a speaker. This required the PCB and some circuitry be configured differently.
In the end the clock’s current load came down to normal parameters, the display was once again bright and the alarm functioned using the standard beeping alarm sound that comes from the LM8560 clock chip. It is sad that the coolness factor of the alarm clock cannot be restored with the honking car sound alarm but my son is quite happy to have his favorite Scooby-Doo alarm clock functioning once again.
The circuit modifications may not have been the cleverest or the best solution, so if you have other suggestions please leave them in the comments below. You can watch the video of the circuit evaluation and repair modifications after the break.
