Réponse à : « LED #1 blinks when connected. iMac not turning on »i have similar problem, but i have solved it. Power supply is good but logic board have a short. That’s why, system is in a power cycle, so led 1 is blinking. Your system try to boot up, but there is an short on your logic board. check the voltage rails from schematics. S0, S4, S3 and s5 there must be and short.