SG300-28P switch non responsive console after firmware upgrade

[MisterPtheNetworkAdmin]

For some projects i have just received two SG300-28P 28 port Gigabit POE manages switches, and we are likely to need some more of the same units. We want to use them in some sets for a simple Dante audio network setup, and  for that they need a simple but specific configuration, mainly disabling EEE, and enabling DHCP on them.

Upon configuring both units, they both were working alright. The first one was a breeze to configure through the web interface. But i discovered a problem enabling DHCP on the second device, as the DHCP server option was inexplicably missing in the web GUI. It seemed the firmware versions of both units were out of sync. So i decided to bring them up to date to keep them all uniform, and tried a firmware upgrade on the first of the two devices using the latest firmware off the cisco website for this device model, sx300_fw-14115.ros.

The firmware upgrade seemed to have completed successfully, but after booting, the units system light keeps blinking, and after flashing all port lights once briefly, the ports all remained dark. And the web GUI was unavailable. 
After buying a veritable collection of db9 cables, i finally found a suitable combination of cables to connect the old style cisco db9 console port to my laptop USB using 3 seperate rs232 cables (somehow a straight db9 cable does not work, and just using a nullmodem cable also does not give me access to the console, but stacking 3 cables and a genderchanger did the trick for some reason).

Now i can see the switch booting in the console, and it seems to load the new firmware version, but before i get a login, it just keeps repeating the same errors, and does not accept any input when this error loop starts: 

08-Apr-2020 13:59:37 %HAL_config_poe-A-POEFailDetected: POE ERROR(write_reg_i2c_internal failed. addr 0x1cd2 dev_num 0 val 0xf44a) was detected
i2c_status fail: 1 retries_num 12
i2c_status fail: 1 retries_num 12
i2c_status fail: 1 retries_num 12
08-Apr-2020 13:59:40 %HAL_config_poe-A-POEFailDetected: POE ERROR(write_reg_i2c_internal failed. addr 0x1cd2 dev_num 1 val 0xf44a) was detected
i2c_status fail: 1 retries_num 12

The only interaction possible with the unit, is during the switch boot process, when i press escape i get the Startup menu, with 5 options; 1. download software, 2. erase flash file, 3. password recovery procedure, 4. set terminal baud rate and 5. back.

I tried using the download software option to transfer the old firmware file version that works on the other unit, using XMODEM transfer in the console terminal, but it keeps aborting the transfer very early, and resumes giving me the same errors:

Downloading code using XMODEM.
i2c_status fail: 1 retries_num 12
08-Apr-2020 13:50:44 %HAL_config_poe-A-POEFailDetected: POE ERROR(write_reg_i2c_internal failed. addr 0x92 dev_num 1 val 0x1c70) was detected

I also tried 'Erase flash file' but it will not let me enter a complete filename for the .ros file i uploaded. It also does not remove anything if i omit the extension of the file, and just reboots into the same endless error loop.

I am starting to fear this unit is bricked. Is there any way for me to fix this unit, when i cannot enter the console terminal to enter commands? Is there any way to factory reset the firmware version? 

[marce1000]

 - I think it's bricked too following https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvj12866 and https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvk55562 , for some reason the upgrade has 'toasted the hardware' , I think you are out of options besides asking Cisco for explanations :
                        https://www.cisco.com/c/en/us/support/web/tsd-cisco-small-business-support-center-contacts.html

 M.

[MisterPtheNetworkAdmin]

After i run the unit for a day or so, i am able to log in to the console, yet the error:
i2c_status fail: 1
keeps being spammed to the console every second. I disabled console logging with 'no logging console', yet the switch keeps spamming to the console. However i am able to write out commands in between the errors and it does accept them, even if the console puts errors between all the characters i input.

Furthermore the web interface does seem to come back online after letting the switch run and spam the error for a day or so, where it is unreachable for the time before that. I even got it as far as to being able to downgrade the firmware from 1.4.11.5 to 1.3.7.18. It loads the older firmware nicely, yet continues the error loop after loading the running config, and again does not accept any input, only after leaving it for hours to a full day, the console will give me a login prompt when i press a key. 

This behavior is all very strange, i just need to unbrick this device and get it to work without erroring out for a day. Is there any 'safe' firmware i can try? This excercize has made me very suspicious of any firmware supplied by Cisco.

[marce1000]

            - I think  the device needs to be replaced ( RMA) , 

 M.

[MisterPtheNetworkAdmin]

Sadly the device is outside of warranty, so i am not able to replace it. I have, however, managed to unbrick it, perhaps someone can use this info.

After letting the switch console error out on the 'i2c_status fail: 1' / 'POEFailDetected' errors for about 30-60 minutes it does continue the boot process in between errors, albeit very, very slowly.
After a while (30-45min), the console will still spam these errors every second, but it will allow me to log in through the errors. Then, after i log in, the console will only spam the 'i2c_status fail: 1' error. At this point the web UI also becomes available again, allowing me to replace the firmware using tftp. I have used this method to try out different firmware versions, and the errors keep happening at every but one firmware version. The only version that still worked, and allowed the device to boot error free, was sx300_fw-12776.ros. This is the oldest firmware version i could find, but it seems it was intended for the non-POE version of this specific model.

While the switch becomes usable again after downgrading to this very old firmware version, this firmware is missing some key features i need, like the DHCP server. This excercize led me to believe there is in fact an hardware issue with this unit, as indicated by the 'i2c_status fail: 1' errors. And even if this issue is circumvented somehow by using the earliest firmware version, it is not solved, as alot of crucial functionality of the switch is not available using this firmware.