HP t420: Hardware 

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The HP t420 was launched in May 2015. In terms of size it harks back to the Wyse Sx0/Cx0 era as the width and height dimensions are similar, it's just a little bit deeper. It has some small rubber feet and is intended to sit horizontally on a desk or to be mounted on the back of the monitor.

Parts of the press release for the t420 read:

...an affordable, cloud-ready thin client for task workers in call center, desktop-as-a-service, and remote kiosk environments. The new HP thin client offers a choice of essential operating system, including Linux-based HP Smart Zero Core and HP ThinPro, and Windows Embedded 7.

The HP t420 is ideal for businesses looking to stay under budget and on task with a reliable solution that doesn't take up a lot of space or make a lot of noise.

The 'under budget' is evident in some elements of the design - The RAM is soldered to the board and the flash memory utilises a USB 3 interface rather than SATA. The data sheet illustrates an issue with having only 2GB of RAM and running a resource hungry OS like Windows:

The use of dual displays attached to models configured with the Microsoft Windows Embedded Standard 7E operating system is not recommended due to the system's limited SDRAM. Less than optimal performance from the thin client and the displays could be experienced.

My t420 has no manufacturing date on it.

Specifications

Processor & Graphics
Type    Speed    Graphics	AMD Embedded G-Series GX-209JA SOC (1 GHz, 2 cores) 1GHz Radeon HD graphics
Memory
Flash    RAM	upto 8GB 2GB (fixed)
Ports
Network    USB    Serial    Parallel    PS/2    Video	10/100/1000 4 x USB2.0 (2 front, 2 rear) 0 0 0 1 x DVI-D, 1 x VGA
Power
Power    Plug    Off    Idle    Running	19.5V 2.31A (label) Coax male 4.5mm/3.0mm + centre pin 0W 6W 7W
Dimensions
H x W x D (mm)	35 x 180 x 140

The embedded operating system is one of:

• HP Smart Zero Core (32-bit)
• HP ThinPro (32-bit)
• Windows Embedded Standard 7E (32-bit)

My example is fitted with Windows Embedded Standard 7E.

Getting Inside

It is a simple matter to get into the t420. First remove the two screws on the back panel. Next, with it sitting horizontally in front of you, press down slightly on the top and slide the top towards the rear by about 5-6mm. You should then be able to lift it clear.

Power Supply

The t420 is supplied with a 45W 19.5V 2.31A DC supply. The connector is similar in style to some of HP's other thin clients, but, I assume because of the small form factor of t420, smaller than usual. It's a dual barrel plug with a centre pin. It looks like the outer of the barrel is 4.5mm with the inner being 3mm. I'm not sure what other devices share this connector.

I did find on eBay an adapter that converts the larger 7.4mm/5.0mm plug down to 4.5mm/3.0mm.

CPU

The CPU fitted to the t420 is an AMD GX-209JA. This is a dual core SOC clocked at 1GHz.

Interestingly enough I couldn't find this CPU on my brief search of AMD's website and neither could their own search engine. As far as Google was concerned it looks like all mentions of the GX-209JA are all associated with the t420, so maybe this is an AMD special for HP and t420?

I also note that that the CPU family/model is reported as 22/0 which is the same as is returned by the GX-217GA fitted to the t620.

PCI

00:00.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 16h Processor Root Complex
00:01.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Kabini [Radeon HD 8180]
00:02.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 16h Processor Function 0
00:02.3 PCI bridge: Advanced Micro Devices, Inc. [AMD] Family 16h Processor Functions 5:1
00:02.4 PCI bridge: Advanced Micro Devices, Inc. [AMD] Family 16h Processor Functions 5:1
00:10.0 USB controller: Advanced Micro Devices, Inc. [AMD] FCH USB XHCI Controller (rev 01)
00:12.0 USB controller: Advanced Micro Devices, Inc. [AMD] FCH USB OHCI Controller (rev 39)
00:12.2 USB controller: Advanced Micro Devices, Inc. [AMD] FCH USB EHCI Controller (rev 39)
00:13.0 USB controller: Advanced Micro Devices, Inc. [AMD] FCH USB OHCI Controller (rev 39)
00:13.2 USB controller: Advanced Micro Devices, Inc. [AMD] FCH USB EHCI Controller (rev 39)
00:14.0 SMBus: Advanced Micro Devices, Inc. [AMD] FCH SMBus Controller (rev 3a)
00:14.2 Audio device: Advanced Micro Devices, Inc. [AMD] FCH Azalia Controller (rev 02)
00:14.3 ISA bridge: Advanced Micro Devices, Inc. [AMD] FCH LPC Bridge (rev 11)
00:18.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 16h Processor Function 0
00:18.1 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 16h Processor Function 1
00:18.2 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 16h Processor Function 2
00:18.3 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 16h Processor Function 3
00:18.4 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 16h Processor Function 4
00:18.5 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 16h Processor Function 5
01:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 0c)
02:00.0 Network controller: Broadcom Limited BCM43228 802.11a/b/g/n

Expansion

The circuit board is shown right. Click on the image for a larger version.

Flash: The flash is relative easy to replace (see below). It's actually as USB 3.0 flash (pen) drive. The flash fitted is a MLC module - just the circuit board without any of the surrounding plastic. According to the data sheet this may be up to 8 GB in size. (I assume 8GB if it is running Windows, a much smaller size if running a Linux derived OS).

My example came with 8GB of flash.

RAM: There are four 512 MB SDRAM memory chips soldered to the system board: two on one side and two directly below them on the other side. You are stuck with 2GB of DDR3 RAM.

USB: Despite the flash using a USB 3.0 interface, as far as conventional USB ports are concerned, there are two sockets on the front panel and two on the rear panel all to the USB 2.0 standard.

Mini PCI-E: The t420 has a Mini-PCIe slot for a wireless network card. Mine came with a such a card fitted.

Links: There are several links on the board between the battery and the DVI socket. E49 and E1 are side-by-side with a link on E49 The adjacent silk screen identifies these as PSWD and FDO. There is an unpopulated E15 labelled BBR that would used to recover from a knackered BIOS situation? (BBR = Bios Block Recovery?) Finally there is a small push button labelled CMOS. See the Firmware tab on how to reset the BIOS.

Click here for a larger photo of the motherboard.

Additional photos

The flash memory is held in place with a black plastic collar. You need lift the catch at the back of the socket and slide the assembly forwards to release the spring clips that are holding the drive in place. On occasion I found this to be a bit of fiddle as other bits of the plastic caught elsewhere on the USB socket.

You can replace this with a conventional pen drive, but do take due note of how yours is packaged.You have about 42mm from the front edge of the socket to where a coil is mounted on the mother board.

Here I've fitted a Sandisk Cruzer blade.

No problems.

Here I've used Kingston Data Traveller. This is too long and so fouls the coil mounting. Also, due to the thickness of its housing, its been pushed high enough to interfere with the top cover and prevent its replacement. Two solutions: Use another pen drive which is a better fit; Take a hacksaw to remove some of the plastic.