[Valve Steam Deck] h4x0rm1k3:
I brought an older LED version Steamdeck today on a whim for £100 which had black screen issues but the touchscreen would work and it'd display using a dock but when not hooked to a dock it was black screen. The thing is, I'd tried near enough everything until I finally stumbled on the answer/s in a Youtube video's comments which ended up requiring the comments of 2 people (from here -)

to get working so a HUGE thanks in advance to Youtube users justinzeng3298 & mikaelrussell1506 as it was both their methods combined that put me on the road to a fully working screen on my Steamdeck again.

My Steamdeck was on firmware version F7A0120 (although I don't think it matters, just do this anyway) so I followed mikaelrussell's method in the 1st part of the guide which will require a dock & TV/monitor so that you can change the required settings -

1st part:-

To update the BIOS you will need to opt into the 'Main' OS update channel:

Turn on Developer settings (steam button > settings > system > 'Enable Developer Mode')

Turn on 'Show Advanced update Channels' in developer settings (steam button > settings > developer settings)

Set Deck to 'Main' in OS Update Channel (steam button > settings > system) Select Apply under 'Software Updates' above on the same screen and then select the 'Restart' once it is done.

After I restarted I still found I had a black screen, damn! So, I then carried on to Youtube user justinzeng's comment and shutdown the deck from the SteamOS power menu and waited until all fans stopped and there was only a solid white LED at the power point. I then proceeded to follow Justins method but found that due to doing a proper shutdown I didn't have to hold the power button for 10+ seconds, I just went straight to the main part holding the vol - , ... buttons & then pressed the power button quickly and released all buttons which was quickly followed by a chime and the white LED started flashing about once every second which continued for about 5 minutes and then it rebooted on it's own and I crossed my fingers.

After about a minute I was greeted with the most amazing sight of the Steamdeck icon being displayed on the Steamdecks screen and not through a dock!!!! AMAZING!!! These are the steps from justinzeng3298's comment to reset the Steamdecks bios/firmware. This worked for me when everything else didn't work. If this helps just one person not go through the pain I went through I will be happy.

2nd part:-

Ensure the device is fully powered down by holding the power button for 10 seconds (I've also read it's 20 seconds but I can't confirm or deny that as I didn't need to do it) or if possible select shutdown from the Power menu when docked.

Once the device is shutdown, hold down both the volume - button and the "..." button, then press the power button once to which you should hear a chime, then you can release all the buttons.

After you hear the chime and then the white power LED light will begin to blink (it may take 5 or more seconds before the blinking begins), which confirms this process is working.

Note 1: This process may take 1-2 minutes to do it's thing start the unit up again during which the display will remain black.

Note 2: The 1st time I tried part 2 was before I knew about part 1 and the LED only flashed a few times, stopped, flashed a few more etc, etc and stopped a lot sooner than 1-2 mins and my deck screen was still black so if you don't see the LED constantly blinking for those 1-2 mins and you still get a black screen then try again until it is constant.

Final thoughts :-

My thoughts on this are that you need to install the newer F7A0121 BIOS version & any OS updates 1st using the developer options and then once that's completed you then need to do a BIOS reset which after that's finished it kicks everything back in to order again! I don't have much background on what happened to my deck apart from it had been upgraded from a 64Gb to a 512Gb drive and it happened sometime after that and it would turn on to a black screen, work when connected to through a dock to a TV and that also the touchscreen still worked.

The inside was fine, all cables fine, battery fine etc, it just seemed like the BIOS had maybe got interrupted during it's BIOS upgrade and it messed with the GPU side of things and re-installing either a newer or same firmware along with a BIOS reset manages to resolve the issue, at least in my case it did. The only other thing I can think it being is that somehow the original drive is tied to the hardware in some form, maybe the drives unique disk HWID because i've seen mention of it happening after a drive upgrade so maybe it depends how you clone the drive initially?.

I'll stop rambling now 'cos I really don't know, all I know is I really do hope this info gets out there and helps more people fix their Steamdeck's that have a issue, I really do!