Well, this took some effort but the steps can be reproduced quite quickly.

The biggest problem is that I can not figure out a way to flash the BOOT ROM without using the serial console cable, which is a big pain in the ass!  I was able to get the application ROM updated using TFTP but the switch was wonky without a upgraded BOOT ROM, so the instructions below cover only the serial console cable method:

    1. Get a serial console cable.  Note that I went through several of them before I found one that would let me SEND characters to the device; I could see the switches boot activity but nothing I typed would appear on the console window… so if you have this problem, get another cable!
    2. Get a terminal program.  Windows Vista and 7 removed HyperTerminal (which is quite annoying) but you can download a free, fully functional version for 30 days from hilgraeve.com/hyperterminal-trial .
    3. Start your HyperTerminal using the following settings:
      connect using COM1 (or whatever port you are using)
      19 200 bits/sec
      8 data bits
      No parity
      1 stop bit
      No flow control
    4. Power up your 4200G (or similar aged 3Com switch)
    5. In the Hyperterminal Window you will see something like, and you will have just a second or two press CONTROL+B to endter the book menu:
      * * * Switch 4200G 24-Port BOOTROM, Version 1.00 * * * ***********************************************************
      Copyright (c) 2004-2005 3Com Corporation and its licensors.
      Creation date : Nov 20 2006, 17:02:48
      CPU type : BCM5836
      CPU Clock Speed : 200MHz
      BUS Clock Speed : 33MHz
      Memory Size : 64MB
      Mac Address : 0017e01f7a40
      Press Ctrl-B to enter Boot Menu… 2
    6. Update the boot rom first, by selecting item 6 (ENTER BOOT ROM UPGRADE MENU)
    7. Select, Type 3 (XMODEM) and a speed of 19200
    8. In your HYPERTERMINAL click TRANSFER, select XMODEM and then select the boot rom file in question, in my case that was s3u02_03.btm
    9. Wait for the file to complete its transfer, then reboot, and notice that the BOOTROM VERSION line should match what you upgraded
    10. Next, upgrade the application firmware by again quickly pressing CONTROL+B on boot
    11. Select option 1 which is ENTER APPLICATION ROM UPGRADE MENU
    12. Again Select, Type 3 (XMODEM) and a speed of 19200
    13. In your HYPERTERMINAL click TRANSFER, select XMODEM and then select the application rom file in question, in my case that was s3t03_02_04s56.app
    14. Reboot and have a nice day.


You may find some of these links useful… I know I did:




http://www.experts-exchange.com/Networking/Misc/Q_21850995.html (scroll to the very bottom)




Jeff · November 28, 2017 at 10:30 pm

I have an issue when transferring via xmodem, it gets stuck on packet #6. Do you know what problem this might be?

hazzmatt · September 15, 2014 at 8:48 am

Thanks Ian, it’s still helpfull in 2014 🙂
It’s save me a couple of hour…

masoud shafipour · September 2, 2014 at 2:34 am

hi after press clt+B
want a password like this command

how to solve or remove this password

    Ian Matthews · September 18, 2014 at 7:27 pm

    Sorry, I do not know.

Questions or Comments?