Welcome to EpoS Wizard!
Spoke to J2, or Aures are they are now, about what you described. They say it's more than likely a main board fault.
i have to agree with Andy we sell lots of J2 with icr and have almost no problems at all with them, i quite liked the 615 though it's a bit old now. certainly a million times better than the megapos stuff we got for a while! almost all of them are dead now 
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We used to sell a lot of J2's but after lots of issues with LCDs failing we've moved away from them.
We now mainly sell Poindus Varipos 715's - an excellent bit of kit in my opinion.
we've had quite a lot of them they're not cheap but we've had no problems with them and they look quite nice too 
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Just to add something here about J2 630s. Had a problem with one again yesterday and it's only two months old.
The green light on the front was flashing but it wouldn't come on. Even unplugging the 19v end of the power supply does nothing. It has to be disconnected from the mains, say about 30 seconds, and then plugged in again. It then starts properly.
