I have RB435G for several years. It was bought as replacement for x86 and never was installed till recently when good old x86 died. I think it had ROS 4.1 but i didn't try it with that version. I update it to 6.42.6 stable using NetInstall and update firmware, then i install 3 wlan cards (2x CM9 and R52H) and configure it. I made several reboots using Winbox and with power cutting off, everything was fine. I installed it and for several days there wasn't power failures so i didn't notice the problem.

Then i realized that each time power fails, after that it wont boot, on board leds are working but lan leds don't or wlans. It is not accessible by mac address either.
Then i simply plug it off and return power jack back and everything is working as normal.
This is happening all time and now it becomes annoying.
Did anyone have similar problem and what was the solution?

Are there multiple partitions? Have you upgraded the routerboot also? Is the power supply providing enough current?

Thanks for reply.
There is only one partition.
Yes, as i said ROS and bootloader are same versions (6.42.9)
I used 12V 1.5A power supply, then i switched to 24V 1.25A but problem remains.

Hard to guess further. Maybe another netinstall could help.

I am guessing it is some sort of hardware failure. Power outages is usually several minutes and after that it wont boot, only on board LEDs works. But then i unplug power for couple of seconds and when i plug back in it boots normally with beep sounds and everything...

Check the capacitors.

Visually they look good...

Pull out the wifi cards and test again. Then put there back one by one and test between. Try more powerful power supply anyway.