Actually may have an ansewer for this question finally. I have first came across this issue way back. The diplay to my TV just one day stop working. No picture what so ever. After calling Nintendo and having a long talk with them. I end up sending the Wii U back to them and they replaced the system. After getting the new system back. A few months after the display again went out. ( May I remind you that the Nintendo was still working on the table. Just no display on the TV with the HDMI cable.) So this time while on the phone with Nintendo. I end up using the componet video cable from the first Nintendo Wii I had sitting around. This end up showing the display again on the TV, but not with the HDMI cable. So again I sent the Nintendo back again and they now replace the Main board. I got the Nintendo back and it worked fine again for a few months... Once of course again the Display went out. Now again on the phone with Nintendo and they haven't a clue on whats going on. So we end up trying the Nintendo on another TV.. I have another Samsung TV up stairs and of course. The display shows up! The HDMI works on the TV upstairs, but not on my main TV down stairs. I have a 32" Samsung LED 1080p TV upstairs and a 46" LED 3D TV 1080p downstairs. The HDMI will not work on my downstairs Samsung ( UN46C8000 ).
I just a few days ago bough a new Denon A/V receiver with 6 HDMI in and 1 out. 3D and 4K UHD pass through. Of course the Wii U does not work on this either. So I'm thinking there is a volage issue with the Nintedno's borad in the system. The HDMI suffers from it later on and the single becomes weak. The TV downstairs can not pick up the single. After the A/V system updated. It can decect a single on the HDMI port, but does not display a picture. If anyone has tried a HDMI Amp or something to this. Please let me know.
@Nintendo... What are you doing to fix this problem. Telling me this is a rare problem, but after really looking around... its a huge problem. Please look into it. I shouldn't have to again for a 4th time send my system in. Or else I will sell this Nintendo and never buy from NIintendo again...