All credits to Daves Jones from EEVblog.
I just copied the schematic , when the Hakko FX 888 is on , a red led blinks only one time every few seconds , when you leave the room and want to check if it's still on , you may look when the led is in the off period.
This mod adds a green led to have a permanant indicator.
The bottom left of the circuit is the I.C. of the unit itself.
It works kinda like a logic inverter
PS : Sorry if my english is bad , it is not my first language.
