Power problem in CADDX RANGER 7600

[Marce Gil]

Hi all,
I have a CADDX RANGER 7600 alarm at home for more than 10 years without problems, but now the red led "Power" is blinking instead of fixed. According to documentation, it is low battery indication, so I've replaced but still the same. Then I measured the voltage that alarm is providing to the battery and I found that it is providing only 13 volts to the battery (measured without battery connected) instead typical 13.8 volts, and I guess that it can be the cause of the problem. There is a variable resistor named "P1" which could set the output power to battery, but I am not sure. Could anyone help?.
Thank you a lot.
http://i.imgur.com/0RswS.jpg
http://i.imgur.com/MdvYK.jpg

 

[Harald Kapp]

Welcome to EP.

There is a variable resistor named "P1" which could set the output power to battery, but I am not sure.

Impossible to tell from the pictures.
After 10 years of service a very common issue is with the electrolytic capacitors in the power supply having lost their capacity. This will result in a considerable AC voltage superimposed on the DC output of the power supply. You made your measurement most probably wuth the meter set to DC. The AC voltage on top of the DC will give you unreliable readings.
Set the meter to AC and measure the AC component of the output voltage (provided your meter is not of the true RMS type which would measure AC and DC).
When you open the alarm, look at the power suply section. Sometimes the electrolytic capacitors show visible signs of ageing (bulging can or lid). It shouldn't be too much effort ti replace at least the big ones by new ones (same voltage rating or higher, same capacitance).
Show us pictures of the power supply section, we may spot a culprit.

 

[Marce Gil]

Hi Harald,

Thanks for your quick answer. After a visual inspection, there is not sings of damage in capacitors, and none AC component voltage in the DC voltage output of the power supply, I measured it with 2 digital voltimeters and also with oscilloscope, and I double check that output power to battery is 13.0 volts DC with any AC component (without battery connected, of course) apart from some milivolts almost impossible to be measured. I am pretty sure that I did it well because I also measured the 12v output for the PCB and detectors, and I was able to measure about 30mv of AC component there.
I take a picture but I am not able to get a reasonable quality...