PowerConnect 2816 - won't finish boot

This switch came to me with the Managed LED always flashing and the switch non-functional. Connected a serial console and can see it get this far:

------ Performing the Power-On Self Test (POST) ------                                                      

UART Channel Loopback Test........................PASS                                                     
Testing the System SDRAM..........................PASS                                                     
Boot1 Checksum Test...............................PASS                                                     
Boot2 Checksum Test...............................PASS                                                     
Flash Image Validation Test.......................PASS                                                     

BOOT Software Version 1.0.0.12 Built  08-Feb-2009  17:19:21                                                           
 Board Type - PowerConnect 2816                               
 PowerConnect 2816 board based on FireFox 88E6218 ARM946E-S processor                                                                     
 64 MByte SDRAM. I-Cache 8 KB. D-Cache 8 KB. Cache Enabled.                                                           

MAC Address   :  a4:ba:db:79:96:c0.                                   

Autoboot in 2 seconds - press RETURN or Esc. to abort and enter prom.                                                                     
  
Decompressing SW from image-1                             
 100%     

OK  
Running from RAM...                   
Operational Mode old state managed; new state unmanaged                                                       
Operational Mode - new mode is unmanaged                                        

*********************************************************************                                                                     
*** Running  SW  Ver. 1.0.0.44  Date  23-Feb-2012  Time  15:52:47 ***                                                                     
*********************************************************************                                                                    
HW version is 00.00.02                      
Base Mac address is: a4:ba:db:79:96:c0                                      
Dram size is  : 64M bytes                         
Dram first block size is  : 46380K bytes                                        
Dram first PTR is               
Flash size is: 8M                 
01-Jan-2000 00:00:03 %CDB-I-LOADCONFIG: Loading startup configuration.                                                                      
Device configuration:                     
Slot 1 - PowerConnect 2816                          

------------------------------------                                    
-- Unit Standalone                --                                    
------------------------------------                                    

Switch stops at this point with the Managed LED flashing constantly. No other LEDs light up which suggests the final (usual?) boot step where all the ports briefly flash never happens.As it hangs at this point and does not finish the bootstrap the switch is not functional (no ports usable, no Web GUI etc).

From the serial console I was able to update to the latest 1.0.0.44 firmware but it will not accept the Boot image update (filename is powerconnect_28xx_boot-10013.rfb), attempting to download (via Xmodem) the updated boot image results in this error.

Error it shows is:

Error 1030000.Wrong image format. Writing aborted.;                                                   
Please contact tech support.                            

I've downloaded several different copies so I believe the image is intact.

I managed to get into the Advanced Menu (Control-Shift-6 + password) and erase the flash memory and reload the 1.0.0.44 firmware (during this process the Managed LED was flashing Red which suggested a fresh install ) but after a reboot it still rejects the new boot image. I also deleted the 'config' flash image hoping that would 'reset' the switch but this had no effect either.

I am hoping the updated Boot image will correct the boot problem outlined above, but perhaps that fault points to something more fatal?

I can also get into the Marvell uBoot manufacturer environment but I have not found any usable documentation to do much from that level although I can switch in and out of that environment using the mfg_setflag 0 command.

Any suggestions on what to try next would be welcome, thanks.