I have a pcb of sprinkler Annunciation Fire Alarm . it is operated on both ac220v /dc 24v.on this pcb 7812 regulator is used . to its common pin2 +24v is given and through a resistance and diode a bc 547 transistor is operated. problem is this i get at pin no. 3 24v dc instead of 12v. due to flash on pcb circuit tracks are burnt and value of resistance is not available. kindly suggest how it works
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