Thanks to all, especially Gordon and TechGuy for detailed instructions on the issue.
Our Roomba561 suddenly stopped charging up and started to show err5 message or asking to "charge the Roomba". The CLEAN button rapidly blinked orange.
I've checked PS output voltage, it was OK, then I tried to connect the PS direct to Roomba's additinonal plug on a side. That didn't work, still blinking orange and not charging the battery.
The battery's voltage shown near 9.5V.
So, I unscrewed a bottom lead and wired up the PS to the battery as shown on pictures above.
After 10-15min I've checked again the batter's voltage and it increased to about 12V. Within another 15min the voltage hit 14V. So I continued.
In about 30min of direct charge I touched battery and noticed that it's became quite warm, so I disconnected the wires and build all back up.
And finally - voila - Roomba came back to life and started to charging up.
so, I'm assuming that the battery might had lost it's power when we left Roomba standing aside, not charging for a few days. So, the battery's voltage droped below some critical point, and it stoped sucking up charge from a PS.
Could be simple as that. Some may experience similar, no big issues with diods or motherboars.