I read few posts over voltage problem, so I replaced original psu with a much better one " 15 Volts " with higher amps.
problem did not solve…
I read another post for disabling “auto negotiation” on interface, did that too.
problem did not solve…
(RB-00 Logs) provides ip to RB-01
RB-01 Logs (750 with every hour or so restart)
If you guys believe it’s OS 5.2 problem, let me know what version is stable for 750 to downgrade? otherwise please guide me the solution!!!
Many Many Many Thanks
Try 5.4. It’s supposed to be fixed in that. Otherwise the latest 4.x is 4.17, and it works great on my RB750G at home.
Don’t see anything about this problem on the changelogs for 5.3 and 5.4—only the port flapping issue affecting RB400 series routers is documented. If it is a software problem downgrading to 4.17 may help, but as other customers are not complaining about this behavior on their RB750 I would suspect a hardware issue instead.
I have downgraded to 4.17 and I think the problem somehow gone. it’s been hours without any reboot, so I’ll just have to wait
little longer to truly confirm it’s software issue.
I hope it’s software, and please don’t scary me by saying hardware 
Scarying you was not my goal, really. 
If you have some time to spend on this issue, you can follow Fewi’s advice and upgrade to RouterOS 5.4; but I would upgrade both RouterBOARDs, not only the RB700 series one, to ROS 5.4. I have not seen anything odd with 5.4 on a RB750G (yet!). Apart of not being a “G” router, the only difference between your router and mine is that your device gets its address from another RouterBOARD so upgrading the operating system on the RB433AH too might help.
Downgrading to 4.17 is confirmed to have solved the self rebooting issue.
Sometimes its just better to stick with older version and not rush to newer OS. hhhh
I’ll wait for a free chance to jump to the new OS 5.4.
thank you all,