Hi, I'm looking for an IC for an old Radio Shack burglar alarm system. Radio Shack tells me they can't fix the system as the IC is bad and they cannot locate a replacement. Any help would be appreciated. Thanks, Bruce
You can replace it with a 3 terminal LM317 regulator: ------- ------- | o | / L78MG | Pins: 1 = Vin = LM317 Vin |_______| | | 2 = Gnd not needed /_______/| ------- 3 = Output = Vout |LM317 || | | | | 4 = Control =* Adj |_______|/ 1 2 3 4 | | | Adj | Vin Vout
The circuit on pin 4 of the L78MG is not identical to the circuit on the adjust pin of the LM317. You will need to know what voltage the L78MG is supposed to provide. The voltage out of the LM317 is set with a
240 ohm resistor connected from Vout to Adj, and a 5K trimpot connected from Adj to ground. You'll wire it like this:
1) Remove the LM78G and install wires from holes 1 & 3 that it occupied to the LM317 pins, as shown
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