Hi guys, I've just replaced the same 4071B IC for the third time.
The output that keeps getting fried is the output of a 2 input OR gate.
The inputs are bridged, so it's really just "on is on, off is off" and is fed from a nand gate which is holding up fine.
See image: https://drive.google.com/file/d/0B24ZN7xs6vYKeS1HX2JxVGRDelE/view?usp=sharing (in my haste I left out the gate resistor 33ohms)
So the output of the OR chip switches an NPN transistor which switches a small relay, which switches a large relay for a compressor.
I've replaced the NPN even though it tested out because I had one, I've checked the relay coil and the clamping diode. IC's are running on, and working with 5V.
The only other elements that I have changed are the clamping diode- it was a germanium diode which I replaced with a smaller germanium diode. Could this be not stopping back EMF supression? I didn't think it was critical to use the exact diode..
I also replaced a ceramic 104 capacitor on this circuit with an MKT 104, again I didn't see that as critical..
That's all I can say about this circuit, not much to it but for the life of me I can't figure out what is causing these 4071's to keep burning out on that same output leg.
Is it worth changing back to larger germanium diodes? Anything else I could check for? Could the compressor itself be effecting anything?
The output that keeps getting fried is the output of a 2 input OR gate.
The inputs are bridged, so it's really just "on is on, off is off" and is fed from a nand gate which is holding up fine.
See image: https://drive.google.com/file/d/0B24ZN7xs6vYKeS1HX2JxVGRDelE/view?usp=sharing (in my haste I left out the gate resistor 33ohms)
So the output of the OR chip switches an NPN transistor which switches a small relay, which switches a large relay for a compressor.
I've replaced the NPN even though it tested out because I had one, I've checked the relay coil and the clamping diode. IC's are running on, and working with 5V.
The only other elements that I have changed are the clamping diode- it was a germanium diode which I replaced with a smaller germanium diode. Could this be not stopping back EMF supression? I didn't think it was critical to use the exact diode..
I also replaced a ceramic 104 capacitor on this circuit with an MKT 104, again I didn't see that as critical..
That's all I can say about this circuit, not much to it but for the life of me I can't figure out what is causing these 4071's to keep burning out on that same output leg.
Is it worth changing back to larger germanium diodes? Anything else I could check for? Could the compressor itself be effecting anything?