Imac replacement screen not working

Guys,

I have an Imac that appeared to have a bad screen. I changed out the screen and still no video. I can plug an external monitor up to the thunderbolt port and get video on an external monitor fine. Any suggestions?
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mikesmithccsOwner/OperatorAsked:
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JohnBusiness Consultant (Owner)Commented:
Is it LCD or LED?  Assuming LCD (I am not sure why):

Screen (you just replaced)
Inverter (to run the screen)
Cold cathode tube (to light the screen)
Interconnections to all these.

Not likely the GPU as the external monitor would not light in that case.
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mikesmithccsOwner/OperatorAuthor Commented:
It is a late model IMac with 27 inch 4k retina display. Not sure about whether LCD or LED, I would also assume LCD. Everything is connected and appears to be seated well. The screen never lights up or shows any backlight. However, an external monitor works just fine. Im wondering if one of the connections on the board has failed.
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JohnBusiness Consultant (Owner)Commented:
I would suspect the Inverter, Cold Cathode tube if LCD.

If LED, I agree it could be a connection on the board (say where the video cable sits)
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JohnBusiness Consultant (Owner)Commented:
Also, I am assuming "screen" meant the glass piece. If you replaced the entire unit, that would include the parts I mentioned. Sorry for my own confusion

So yes, look at the connection points on the mainboard.
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Mre MartinCommented:
if it is Inverter anyway there will be video on screen just very very dim.
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mikesmithccsOwner/OperatorAuthor Commented:
At this time I have sent the "replacement" screen back, as I believe it may also be bad. Going to try another and see how it goes.
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