7 LED chaser slightly modified

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http://forum.allaboutcircuits.com – I have built a 7 LED chaser circuit running on 18V. I changed one LED for a copper coil to run an electromagnet but it didnt have enough power, then i added a darlington pair I had from the early 90's never used before the same output and it worked for a bit i added a switch so it could be turned on and off but after a few days it had stopped working. So i changed the output back to an LED and still didnt work then i changed the two old school transistors for more recent ones four different ones of the same type and model, the lights work but when the coil is put back i get nothing from the (Embedded)