Any update on how to identify the bad units?
Please email support if you received such bad device at the MUM! support@mikrotik.com
That is some great information. If Mikrotik is working on a way (or hopefully by now, has come up with a way) for distributors to easily identify the bad units, I would love to be able to test my other (9) RB751’s to make sure they are ok before putting them out for retail clients where one of mine bricked in less than a week just using it at my own office. Any documentation on that would be much appreciated!
Thank you for your time and assistance.
turn them on. if there is no blinking - they are fine. that’s it.
The problem with your reply Normis is the issue will start not necessarily the first boot.
We use these for commercial sales so so far, not a good thing to happen but the product is good.
I bought 60 for my customers because it works very good with the IPAD.
This is a very limited issue, it only affects the very first devices. Our of all manufactured RB751s, the affected percentage is miniscule. You should stop worrying about it. We fixed the issue already in October! That’s around the time they started shipping!
3 of my last 4 bricked. One out of the box first boot, one in two days uptime, third in two weeks.
Any serial numbers for bad boards?
Application of 24v to the board seemed to bring them back from the dead.
…but only temporarily, unfortunately. Went into seizure mode after 2 days in service.
please contact support@mikrotik.com and write the Serial numbers of thos board so we could check if they could be affected by that problem.
Done. Thank you
Normis, i doubt that. We just bought 5 of the RB751 devices and one of them is having this blinking and not coming up (it worked for 2 minutes after first powering it and then it crashed and since then its dead). The other devices all have 5.16 installed which was released in May 2012 and i dont think that the distributor updated them before shipping.
Is this (known) issue always a DOA or can it happen anytime? 
Regards,
Joerg
As far as I can tell, it can happen anytime. I had two boards ready to RMA back to my vendor (on MT’s advice). One was DOA with flashing LEDs, the other was programmed and put into service but developed flashing light syndrome after one day-no reboot or power cycle involved.
I decided to power them back up one last time before I dropped them in the mail. Used a 24v POE. They both booted up normally. I switched to the shipped 12v power supply and they both rebooted normally.
I find it very hard to believe that all the 751U’s I’ve bought over the last year are all part of “the very first devices”. According to MT support, they do not have a serial number list of affected boards. It’s a very annoying and random problem it seems. The easy answer is “stuff breaks-send them back”. But in my experience they can develop this problem at random and anytime. The answer Normis gave that if you power them up and they boot normally, don’t worry, they are fine is not correct.
I received one today and opened it, updated it to 5.20 run for about 3 hours and BOOM lights blinking. Should i get another type router.
Probably about time for an MT staff comment…
Reveived 5 pcs yesterday, all dead, all leds blinking. Sent mail to support.
So it is not correct that this issue was solved!
100% broken??? WOW!!
It seems that there is no real quality control
sounds highly unlikely, maybe something else was wrong. will check that ticket
well.. what “something else” should it be??
Reflashed the fw by netinstall on 4 units with 24V connected power supply and now working OK with shipped power supply.
The worst thing Mikrotik can do is not to tell anyone what is the problem and just say RMA.
You need to understand that we are not just buying/selling, but we are installing and this costs us money because we send technicians and also reputation is not good.
I’m leaving these 4 pcs for internal use and not buying anymore. 1 pcs was allready sent for RMA and they report they will reflash it.
These units were working OK, configured by quick-set, updated FW do 5.21, after they were taken to customers site, the did not start anymore.