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,
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.