RB751U-2HnD doesn't boot after upgrade

Hardware MikroTik hardware general
1

Hi All!

I tried to upgrade RouterOS on my MikroTik RB751U-2HnD, and after that it became totally unmanaged.
I can’t see it on winbox and netinstall, when connect directly to PC its ether1 (PoE) port, and there is no any network activity on PC NIC (like message that ethernet cable is connected).
I tried to restore factory defaults (by resetting button and reset jumper hole) and have no luck with this too.
The symptom is following: all LEDs on board lights permanently when I power on device.

I realized that if I hold reset button before powering on, and hold it for some time when device boots, ehernet and WLAN LEDs turns off, and only PWR and ACT LEDs continues to glow. I guess that bootloader is still alive, but RouterOS is corrupted.

Are there any ways to resolve this problem and fix device?
How can I connect to serial port of device to see its bootloader? I tried to google RS232 pinout of this device with no success.

2

See link below, on resetting, netinstalling etc.
Also try various versions of NETinstall.
FYI, ether1 is a DHCP client…

http://routerboard.com/pdf/357/rb751U-2HnD-ug.pdf

3

Thank you for your answer.
I already read this doc and did did the described procedures to reset the device.
Also thanks for info about Ether1 (read about it the following: “The Ether1 port has a firewall on it, and a DHCP client, so it’s configured to be connected to your ISP.”), I will try various versions of Netinstall with Ether2-5 ports.

But what about permanent glowing of LED indicators? What does it mean? Does have anybody according info?
How to get serial console to work on RB751U-2HnD?