RB751 bootup problem

RouterOS General
1

Hi,

I have an RB751U-2HnD which has a problem rebooting.

The problem is that each time it tries to boot, it seems to go through its POST, and then all I get is a link light for ether1, the power light, and no other lights, and nothing works. My guess would be that it’s stuck in the bootloader, and the only solution I’ve found is to do a hard reset and then restore the config from a backup. It then works until the next reboot. It’s very hard to diagnose anything without a serial console! (This is something I find extremely annoying with 751s — I’d rather have 4 Ethernet ports and 1 console port, than 5 Ethernet ports and no console at all, but that’s a rant for a different post.)

Has anyone seen anything similar?

Is this fixable, or do I need a new 751? Could this be related to the power issue that I’ve seen discussed elsewhere? Is it worth trying to find a 24V power supply, or should I just get a new board?

(I don’t have time to sort out RMAs at the moment, and it’s in a different country to where I bought it, and I really need it working.)

Thanks!

Alex

2

I’ve the same issue: I found the problem on three different RB751 and using different power supply (12V/1A and 18V/1A).
Any suggestions will be appreciated!

Thank you,
Alberto

3

I’m having the exact same issue with my 751U. I have read other forum posts that suggest that this problem only started with ROS 5.13 and continues in 5.14.

One thing that I found is that if you go to SYSTEM > ROUTERBOARD and then click SETTINGS, my CPU Frequency was set to 250MHz. I’ve changed CPU Frequencies on other boards without any issues before, but for some reason this seems to be causing the problem here. After I changed that setting to 400MHz, I have rebooted my board at least 5 times without any issues.

4

Thanks for the reply. I’m glad I’m not alone, at least. :slight_smile:

I’ve never touched the CPU frequency setting, though, and I’ve just double-checked and it’s set to 400MHz. Have you tried 5.12, if the problem started with 5.13? If that fixes it, that would definitely be the simplest option, I doubt I’m using any features that appeared since 5.12.


Alex

5

Well, I downgraded to 5.12, and, so far, so good. I’ve rebooted three times so far, and it’s all been fine, so fingers crossed!

It looks like everything I had working on 5.14 is working on 5.12, the only thing to watch out for is that if you use certificates (I use them for IPsec/ISAKMP), you’ll need to run “/certificate reset-certificate-cache” (as per the release notes for 5.14) and re-decrypt your private keys.

I’m glad there’s a simple solution (and let’s hope this solves the problem permanently), and many thanks for pointing it out! I hope MT are aware of the problem…

Alex

6

What version are you running? Try 5.12 or earlier, that seems to have fixed it for me.

Alex

7

Same problem here on 4x RB751U’s.

Units are stable on V5.12, but have boot up problems on v5.13 and V5.14.
I read another post where the problem still occurs on latest V6 beta as well.

Certainly looks like a firmware issue.

I hope MikroTik can identify and resolve this as soon as possible!

8

I had the same problem with routerboard boot loader v.2.38 and ROS 5.xx.

Solution to fix it:

  1. Downgrade ROS to 5.11
  2. Upgrade (formally downgrade) routerboard boot loader to version 2.37
  3. Upgrade ROS to 5.15
  4. Reset configuration and load backup to the router
  5. Test it!
9

I’m running ROS 5.12 and boot loader 2.38, and it’s working fine.

Alex

10

Hi, how can I downgrade ROS of RB751G back to 5.11?
After updating it to 5.14, Winbox doesn’t see RB751G, and I can’t see it in netinstall.
Help me, please

11

This issue was fixed in RouterOS v5.15, but we will release v5.16 today, so please wait for that. You will need to use Netinstall for upgrading, if your device is non responsive.