Fixing a Roomba that doesn't want to charge or dock

My Roomba 780 has been spinning around the house for years without any issue, until last month. It was just sitting there in the middle of the room with a dead battery when I came home. Placing it manually onto the dock didn’t trigger the charging led and having to plugin manually the charger each time was a pain in the ass. This evening I decided to investigate the issue.

Symptoms

  • Roomba not charging in the dock when placing it manually
  • Roomba not docking correctly - wheels keep on spinning and roomba is hitting the dock
  • Roomba charges fine with the DC connector on the side, so the battery is fine
  • Common solutions like cleaning the dock connector don’t work

The issue

First measure the voltage on the dock. It should read about 2.9 volts. If it doesnt the dock is probably screwed and this guide won’t help you. When the correct resistance is applied accross both terminals the dock will switch over to charging mode and up the voltage to about ~22 volts.

The resistance is controlled via the charging board in the Roomba. To prevent a short circuit it checks if its charging via both the dock and the DC terminal on the side. When a plug is inserted

The fix

I took the entire Roomba apart and cleaned it. It collected a lost of dust over the years! Then I inspected the motherboard for blown components, but couldn’t find any. I discovered that the minus-terminal of the dock conncetor leads directly to the DC plug, so I started investigating there.

The DC plug has 3 wires: + (red), - (black) and a switch-wire (brown). Internally in the DC connector the switch-wire is connected to the ground. When a DC plug is inserted this connection gets interupted. This is how the Roomba knows via which way it’s charging.

I bypassed the faulty DC plug by soldering the black & brown wire together and this fully restored charging via the dock connector. Please not that you’re now bypassing the charging protection. You should make sure that you never charge your Roomba via both the dock & the DC plug on the side. To make sure this wouldn’t happen in the future, I removed the positive wire from the connector too. A nicer solution would be to replace the connector with a replacement part.

Protip: if the charging icon is blinking amber very fast (2 times/second) you can reset the entire Roomba by holding the ‘clean’-button until the display shows ‘RST’. Confirm by pressing ‘clean’ again.

Shorting the brown & black wire of the charging connector with a screwdriver

Permanent fix