Solution to "no HDMI signal" black screen on TV kind

I’m posting a solution I found to a problem I had been having with a previously working S905x box.
I was about to bin the box but I managed to figure out the cause and fix - I’m sharing it in case it helps anyone else in the future.

A box that was previously working 100%, suddenly would no longer produce a picture on my 4k tv. I would get a “no signal” error on the TV. I tried different HDMI cables, and ports on the TV, but stlll a black screen on the TV. I don’t know of anything that would cause this.

Anyhow, I then tried re-installing the stock Android image, but still no luck. I tried using an older 1080p small screen TV and everything worked. Still it would not work with the 4k tv. I set up the internet connection using the small TV and then I SSH’ed into the box.

Just for grins, I thought I’d check the following :- “fw_printenv hdmi_mode” and “fw_printenv output_mode”. The returned message for both commands was "hdmi_mode not defined" and “output_mode not defined”. I have no idea how these u-boot variables were wiped, but that was the cause of my problem. I fixed the issue with “fw_setenv hdmi_mode 1080p60Hz” and repeated the command for “output_mode”. Now everything is working 100% again.

So, if you are faced with a black screen in the future and have tried swapping HDMI cables and ports, then SSH into your box, and run the “fw_printenv” command for “hdmi_mode” and “output_mode”, to see if your issue is caused by wiped out variables. It may save your box from being thrown in the trash - as it did for mine, :grinning:

As I said, I have no recollection of any reason why these values would be wiped - maybe I had a power surge on the box - but this happened several months ago, and I only managed to stumble upon the solution today. Fortunately this was a ‘reserve’ box. For some reason, the older 1080p tv did not “care” that these variables were wiped (but the 4k tv did care) - otherwise I may not have been able to guess at a solution.

I have had the same issue for 2 or 3 weeks on Samsung KS9000 and also on an old Samsung LCD but only with N2 and all operating systems.It happens the same with all of them,you see it boot on the tv then no signal.Connecting to msi and Viewsonic monitors works as expected,almost ordered another N2 and butchered the other one for spares.Nice spot cheers