My home security system is powered from a 240VAC to 16VAC transformer, with a 12VDC backup battery. The system rectifies the 16VAC providing an output DC voltage running to the control panel at around 15.5VDC.
The system has been switched off for over 2 years, and I'm getting it going again. Having replaced the backup battery, I fired it up and found that running off the battery (ie. transformer switched off at the mains power outlet), the system works fine. However, when I run it off the transformer, the control panel stops working.
The control panel contains a 7805 voltage regulator (spec'd to output 5VDC from input voltages up to around 36VDC). When running off the backup battery only, the input voltage at the 7805 in the control panel is 12V, and the output voltage (as expected) is 5V. When powered from the transformer, the input voltage at the 7805 in the control panel is 15.5V, however the output voltage measures at 1.3V (which is obviously not what is supposed to happen, expecting 5V output irrespective of the input voltage).
The question is: is the problem likely to be caused by a faulty regulator? ...(if so, why does it work with 12V at the input?) ...or is it more likely a result of the filtering/smoothing capacitors on the circuit board not the regulator itself? ...(if so, please explain the likely cause)
If you have a solution / thought on the cause of the problem, I'd also like recommendation(s) on what / where I should measure on the circuit board, or what else I can do to confirm the cause.
The system has been switched off for over 2 years, and I'm getting it going again. Having replaced the backup battery, I fired it up and found that running off the battery (ie. transformer switched off at the mains power outlet), the system works fine. However, when I run it off the transformer, the control panel stops working.
The control panel contains a 7805 voltage regulator (spec'd to output 5VDC from input voltages up to around 36VDC). When running off the backup battery only, the input voltage at the 7805 in the control panel is 12V, and the output voltage (as expected) is 5V. When powered from the transformer, the input voltage at the 7805 in the control panel is 15.5V, however the output voltage measures at 1.3V (which is obviously not what is supposed to happen, expecting 5V output irrespective of the input voltage).
The question is: is the problem likely to be caused by a faulty regulator? ...(if so, why does it work with 12V at the input?) ...or is it more likely a result of the filtering/smoothing capacitors on the circuit board not the regulator itself? ...(if so, please explain the likely cause)
If you have a solution / thought on the cause of the problem, I'd also like recommendation(s) on what / where I should measure on the circuit board, or what else I can do to confirm the cause.
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