Back during the 2011 Las Vegas MUM, I received an RB751U that did the same thing: worked for about 24 hours, then did the "blinking lights" thing. I hooked up a different power supply to it, and then it started working again. So I hooked the original power supply back up, and it still worked with that! After hooking up the different power supply to it (also 12V, but more amperage), I also noticed the burning smell that others here have commented about, and even noticed a small puff of smoke escape from the device! After that happened, the "blinking lights" problem stopped and it seemed to act normally.
I mentioned this to Normis at MUM, and he told me that they didn't know yet what caused it but they had one back at headquarters in Latvia that was doing the same thing that they were studying. I guess I should have asked for them to swap out my 751U, but I did not. Amazingly, it is still working to this day; I am posting this message to the forums while connected to it!
Normis has made two claims in this thread:
1) Switching power supplies is not a fix. The routers with this problem still need to be repaired.
2) This problem only occurred in early batches, and was fixed very quickly in newer batches.
#1 makes sense. The "puff of smoke" suggests that something in the router is burning up and was probably defective to begin with. Interestingly, though, we have run into a few 751U routers that had the exact same thing happen to them, and in each case, after the "puff of smoke", the router starts working normally again and continues to do so indefinitely!
#2, though, is unfortunately not true. We have run into several 751U routers that do this, even recent ones. I know that some of the routers we received with this problem more recently are newly-manufactured ones that came out after MikroTik claims they fixed the problem, and I know this for the following reasons:
1) The MAC address begins with D4:CA:6D, not 00:0C:42
2) The MMCX connector on the front sticks out like the new ones, instead of being flush with the case like the old ones
So there are still RB751U being manufactured that have this problem. Fortunately it does seem to be a small percentage.
The question that still remains is, what exactly is going on with these routers? There must be a defective component that is perhaps drawing too much power, and eventually burning itself out (?).
The last time we ran into a router with the "blinking lights", I decided to take it apart before I plugged a different power supply into it, so that I could see where the smoke was coming from. When I plugged the new power supply in with the plastic case off, I saw that the smoke came from underneath the wireless RF shield. Unfortunately, I did not think to remove the RF shield before applying power to the board, so I was not able to see what burned up underneath the shield. I removed the shield after the smoke was gone, but I didn't see any burn marks or charring. The next time I run across one doing the "blinking lights" dance, I will tear it apart AND remove the RF shield before applying power, and be careful to observe exactly what is burning up.
Whatever it is, though, it apparently has something to do with the wireless part of the RouterBOARD. Is it the amplifier?