Microtik RB750Gr3 - cyclic reboot when ISP cable is connected to WAN port

Hardware Questions and Recommendations
1

Hi,
I installed OpenWrt 23.05.0 on Microtik rb750gr3. I have a weird problem with booting the device.
I connect a cable from my ISP to WAN port and then power up device. USR LED starts flashing and suddently the device reboots, and again and again. So I have a cyclic reboot.
If I disconnect cable from my ISP or connect it to another home router or connect ISP cable to LAN port the device boots successfully and works fine.
The problem occurs only when device boots and when ISP cable is connected to WAN port.
Microtik router has PoE-in on the WAN port I think this may be an issue.

I have alredy read this topic - OpenWrt installed MikroTik RB750Gr3 won't boot when WAN cable plugged
but didn't help me,
I have this output in console:

OpenWrt 23.05.0, r23497-6637af95aa
 -----------------------------------------------------
root@OpenWrt:~# for i in /sys/firmware/mikrotik/soft_config/*; do echo -n "$(basename $i): "; cat $i; done
bios_version: 6.48.7
boot_delay: 1 [2] 3 4 5 6 7 8 9
boot_device: eth [flasheth] ethonce flash cfg cfgonce
boot_key: [any] del
boot_proto: [bootp] dhcp
booter: [regular] backup
commit: clean
cpu_mode: [powersave] regular
cpufreq_index: 0x00000370
silent_boot: [off] on
uart_speed: off 1200 2400 4800 9600 19200 38400 57600 [115200]

I don't see anything suspicious here.

Any help would be appreciated

2

I've had the similar experience when another vendor's hardware started to go. Have you tested if you can reproduce this with the vendor software?

1 Like
3

I used RB750gr3 with vendor firmware for a very short time. It worked fine then I changed vendor firmware to OpenWRT. But I didn't pay attention if it booted correctly. May be I just connected ISP cable after it had booted. I'm not sure.
Now, to test the router with vendor firmware I should restore firmware. If I don't find the solution I will test it with standard software.

4

I just excluded LAN1 port from LAN bridge and connected cable from my ISP to LAN1 port. Then I established the internet connection. WAN port is not connected. The device works fine and stable.
So this is my solution for now. I'm looking for a better solution.

Any help would be appreciated.

5

Hi,

I have had installed OpenWrt 21.02.3 on my rb750gr3 devices and sometimes in the case after i reflash a firmware image to a device.when the wan cable plugged USR LED flashed but not booted. If i apply a hard reset it works as expected. Could you try to install old version like OpenWrt 21.02.3 and try the same scenario.