Whelen Alpha 12 siren amplifier

kustern

Registered Member
The unit I have quit working. I have tried to find the cause without luck so far. I can't figure out how the low voltage (5V dc) works or actually how it gets it's input voltage. The voltage regulator (LM78L05) does not get any input voltage (12V dc). When I apply 12V dc at the regulator it works fine and provides 5V dc, but still no sound!

Does anyone have a schematic or any info that may help fixing my unit?

Thanks
 
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kustern

Registered Member
pics of the voltage regulator location LM78 and also a pic from the backside of the circuit board with some notes of measurements I have done
 

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kustern

Registered Member
There is a Tyco relay that connects one point to 12v battery power and I feel this should also provide power to the LM78L05 voltage regulator! I can only measure connection to one point that doesn't go to any component! What am I missing??
 

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kustern

Registered Member
found the problem, it was a trace on the circuit board that had a bad solder connection and over time heated up and disintegrated.
 

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