Wii u powers up but does not display on tv

just bought a few faulty wii u, fixed one but the other has me stumped.
I plug it in and it sounds like it boots, blue light, takes in disc but nothing displays on screen. Because it does not display on a tv i can not sync a gamepad to it.
Ive tried on different tvs, different hdmi and also tried the av lead and nothing?
Ive read through a lot of old threads and all seem to say they ended up sending back to nintendo?
I was hoping someone might have more of an idea, maybe a chip needs replacing? i have the tools to do and happy to experiment but need to pinpoint specific chips to be looking at?
I thought it might be the hdmi but as the av cable does not output it must be something else.
any advice would be great, would be nice to try and fix rather then just reselling as faulty again.

 

i have tried that but it says to input the symbols displayed on the tv, but can not see them, tried guessing but, im not that good!!

 

so after having a further read i came across the ifixit tear down and see the different chips
there is a hdmi controller chip. is anyone aware of a reason why i could not take one off a working(bricked) wii u and place on this?
i have pretty decent solder skills and a hot air reflow station so swapping the chip is possible but is it likely to sort the fault?
its a big tear down x2 if its for nothing?

 

Just an update, the console that would not display anything I planned on doing a chip swap, when I turned it on to check which console was which it booted and is now working fine?
The plan is to still to do a chip swap, I just need another console that does not display waiting for some cheap ones on ebay ..