T620 Thin Client: Bizarre (pseudo?) hardware problem

[ThinWilly]

Apologies for the length of this post, but the issue is puzzling, and if you keep reading, you will encounter at least 1 astonishing event.

I’ve successfully installed Debian 12 on two HP T620 thin clients, but then on the next boot, there are failures that at least act like hardware problems. That seems incredible - no way just installing the OS could trash the hardware, right? Besides, others report installing Debian on this model without problems (https://www.parkytowers.me.uk/thin/hp/t620/linux.shtml).

The saga: I bought a T620 on eBay. Some adapters were needed: a PS/2-to-USB adapter for the keyboard, and a DisplayPort 1.2-to-HDMI for the monitor.

I booted it with a USB stick first with Sparky Linux just to see if it worked, then a USB containing debian-12.0.0-amd64-netinst.iso (installs Debian, pulling needed files from the internet). Install went smoothly. To boot into Debian, 2 further steps were needed: 1. copy /EFI/debian/grubx64.efi to /EFI/boot/bootx64.efi. (Reportedly - see link above - the T620 looks for the .efi file in a nonstandard place), and 2. set BIOS to enable Secure Boot (and disable Legacy Support). Copying the .efi file requires booting from a USB drive (Sparky Linux again). After these 2 changes, it booted right up in Debian. I added some users, verified the ssh server. installed a couple utilities, made the IP address static. Finally I shut down (using shutdown -h now).

Next morning, I powered it up. No boot, black screen; the only activity was that the keyboard LEDs flashed twice and numlock stayed on (I had set that in the BIOS), then it emitted beeps and red-LED flashes in groups of 6. No response to repeatedly pressing keys during power-up: F1 (for system info) or F10 (for BIOS setup) or esc (for a “fast test”; not sure if this applies to the T620). The HP manual http://h10032.www1.hp.com/ctg/Manual/c04034585 says that sets of 6 beeps mean “Pre-video graphics error”, and the fix for models with a graphics card is to reseat or replace the graphics card. I tore it down and found that there's no video card; graphics are on the motherboard.

Now the astonishing part. I posted a positive review on eBay briefly describing what happened, and saying it wasn’t the seller's fault. 8 days later, another T620 showed up on my doorstep. The vendor evidently saw the review and decided, unasked, to send a replacement!

History repeated itself. Installed Debian from the same .iso, After the successful install, including an XFCE desktop, I shut down. Came back 3-4 hours later, powered up, The same 6 beeps as a week before!! Unplugged all peripherals, same beeps. Removed the RAM card, now it was 5 beeps (meaning “pre-video memory error”) instead of 6. Removed the solid-state disk. Tried booting from the Sparky Linux USB. Beeps in 5's. Reinstalled the RAM card, tried again with Sparky. No beeps. I connected monitor and keyboard. Monitor shows an error (valid) due to no bootable disk. (With Legacy Support disabled, it can't use Sparky, and the SSD with Debian was still removed.) It also said press F2 for diagnostics. It passed the Memory Quick Check.

I’m reluctant to power it up again until I have some idea what’s going on. The chance is minuscule that 2 of this computer would coincidentally experience a random hardware failure like this. But somehow it thinks there’s a hardware problem. I just have 1 idea: in the BIOS settings, Power-On Self Test Messages were disabled; I enabled this - mistake? Seems unlikely to be the problem. That, and setting NumLock to be On at startup, are the only BIOS changes I made, except the changes needed for Secure Boot.

There is a pushbutton on the motherboard that I think resets the BIOS to defaults - anyone know if that’s correct? I guess that’s 1 thing I could try. Good idea?

Thanks for reading to the end; any suggestions are much appreciated.

[ThinWilly]

Installing Debian 11 "Bullseye" rather than 12 "Bookworm" seems to have resolved everything. Thanks to lewulff on forums.debian.net, who said "there are some differences between how Debian 11 and Debian 12 work with UEFI".