The t820 I bought was described by the seller as:
Has power & green light on board, but beeps & won't send picture to screen.
As it had lights and beeped it sounded to be worth the risk and so I hit the 'buy' button.
On arrival I plugged it into an HP 90W PSU and sure enough the t820 sat there beeping - four beeps, a pause, then four beeps, a pause....
Consulting Mr Google I discovered in the t820 Maintenance and Service Guide on page 75:
Activity Beeps Possible cause Red Power LED flashes four times, once every second, followed by a two second pause. Beeps stop after fifth iteration but LEDs continue until problem is solved. 4 Power failure (power supply is overloaded).
OR
The incorrect external power supply adapter is being used on the unit.
A quick look at the datasheet provided the answer:
Power High efficiency, Integrated graphics: 135 W 87% efficient active PFC
Discrete graphics: 180 W 87% efficient active PFC
So the t820 needed a 135W or 180W PSU. With a 135W power supply things moved on to the next issue...
On power up I was now presented with the following screen:
Copyright (c) 2013 Hewlett Packard Development Company L.P.
Version 2.15.1236 Copyright (C) 2013 American Megatrends, Inc.
8192MB
Default settings loaded
161-Real-Time Clock Power Loss
The system time is invalid. This may be a result of a loss in battery power.
Set the correct time and date using your operating system. If this message
persists, you may need to replace the onboard battery.
162-System Options Not Set
Your system configuration has changed since your last boot. Addition of a
hard drive, etc., or loss of power to the Real Time Clock has occurred.
Pressing F1 will record the new configuration. If this message persists, you
may need to replace the onboard battery.
v02.53 HP t820 Flexible Thin Client
F1 : Boot Press the ESC key for the Startup Menu
So I replaced the CMOS battery and rebooted....to get the same screen. A control/alt/del followed by the ESC key got me to the startup menu:
Startup Menu Continue Startup System Information Change Language Diagnostics (F2) Boot Menu (F9) Computer Setup (F10) Network Boot (F12) ME Setup (CTRL+P) Utilities Run UEFI Application...
As noted elsewhere my t820 had been wiped clean, there was no OS installed. I did discover I was able to boot Tiny Core Linux from one of my USB drives, but on power up the F9 and F10 keys did nothing. Trying different keyboards didn't help. Setting the correct time and date in Tiny Core Linux did nothing to get rid of the power-on system time invalid message. What ever I tried did nothing. I could not get into the BIOS.
To cut a long story short what I needed to do was select the Utilities option on the startup menu.
This brought up:
UtilitiesSet Time and Date Flash System ROM ESC=Exit
I selected 'Set Time and Date' and once these were set things return to normal - the F9 key brought up a Boot Menu and the F10 key took me into the BIOS. Why an unset time and date caused such grief I have no idea.
My t820 was running BIOS L01 V02.53 10/20/2014. Checking I found that the latest BIOS was L01 V02.70 (sp77880.exe). I downloaded and unpacked sp77880. From a quick survey of the options available the most straight forward one was Startup Menu / F10 Setup BIOS Flashing which was described as:
The HP Business Desktop systems provide a BIOS upgrade option through both the Startup Menu and the F10 Setup utility using the "Flash System ROM" feature. Reboot the PC and press the Escape key to display the Startup Menu. Use the arrow keys to select Utilities, and then select the Flash System ROM option. Alternatively, reboot the PC and press F10 to access the BIOS Setup utility. In the File menu, select Flash System ROM. Either method requires that removable media be present (USB storage or data CD) that contains the BIOS binary image file in the root directory. The binary image file can be found in the DOS Flash folder and is named xxx_MMmm.bin where "xxx" is the BIOS family, "MM" is the major version number, and "mm" is the minor version number. To create a CD for updating the BIOS, use a blank CD-R or CD-RW disk on a system with a CD-RW or DVD+RW drive, and write the binary to the disk using any CD-burning software (Windows 7 and Vista support burning data CDs without additional software). If a BIOS Setup password has been set, the password will be required before being able to access the "Flash System ROM" menu. The user is notified when the process is completed. The new BIOS code will not take effect until the PC is restarted.
It was then just a matter of copying the L01_0270.BIN file to a USB drive, plugging it in and then following the on screen directions. (I went via the ESC/Flash System ROM route).
My update proceeded without a hitch.
The UEFI BIOS (with Legacy support) includes the usual options. Things of note as I browsed through the options:
As noted in the hardware section any BIOS password can be reset to removing jumper E49 (also labelled PSWD) and briefly rebooting the t820 before replacing the jumper.
Caveat When a password is set the user has the option (via menu option Security -> Password Options) to mark it as a 'Stringent Password'. If this is the case then jumper E49 is ignored by the BIOS and the password cannot be reset.