Portserver TS 4 upgraded with wrong POST now won't boot.

Is it possible to recover?

You can try restoring the OS via TFTP.

You will need to get your previous version of firmware (ftp://ftp1.digi.com/support/firmware) and a tftp server. If you do not have a tftp application you may use the Digi tftp application located here:
ftp://ftp1.digi.com/support/utilities/tftpd.exe.

To use this application put the binary firmware image in the same directory as the tftp executable and then double click on the tftpd.exe executable to start the tftp service.

To enter the Diagnostics menu on the Digi you will need to make sure you have a null modem cable between your PC and the Digi as well as an Ethernet network connection.

The first thing you will do is open a hyper terminal session (or another terminal application such as PuTTy for Windows 7 and later) to that COM port (typically COM1) at 9600 baud, 8 data bits, no parity, 1 stop bit, and no flow control. Once the port is open make sure to leave the focus on the hyper terminal / terminal application window.

In the next step you will need to locate the reset switch.

The next part can be tricky, and you may wish to get a partner to assist you. First you must un-plug the power to the device, wait one moment, then plug the power back into the device. Once you see the power light flash once, press and hold the reset switch. While you hold the reset switch press the v (lower case v) key once every few seconds on your keyboard until the diagnostics menu appears in the window. The diagnostics menu may take up to a minute and a half to appear. Once it appears, you will see the menu scroll by a number of times

When the diagnostics menu stops scrolling by you will want to press C (shift c) to tftp a new image into the firmware. You will then be asked for the image name and this will include the .bin extension. Next you will be asked for a temporary IP address for the unit, a submask, and a gateway. Then you will need to enter the IP address for the tftp server (or your PC running the tftp service). Finally you will be asked to confirm the information you have entered. Once confirmed the Digi One will attempt to download the firmware image via tftp from your tftp server.

If it is successful the current firmware on your unit will be erased, and the firmware you have downloaded will be written to flash. Once the Digi One has finished writing the firmware to flash (this will take a few minutes) it will attempt to start up using the new firmware image. If successful the power light will come on solid (will no longer blink in the 9-1-1 pattern) and you will be able to communicate with the device and load the current POST, and then reload your new firmware image. Please note that the above firmware file name is an example. The actual firmware file name may have an additional 0 or a different letter revision.

If this does not work to recover the unit, the only other option is to have it sent into Digi for recovery.