IRobot Roomba 620 wheel replacement

@cbenish try a few things first based on this “both spun the same until I put them in. The left on is a bit stiffer.  “

Check the wheels for obstructions.

Push the wheels up and down several times and shake out any loose debris that may be trapped in the wheel well.

Make sure the wheels turn freely.

The other thing to consider is dirt/grime at the optical encoders that sense wheel motion. Take a look at those and clean those with some isopropyl alcohol. Last but not least, you can also check the drive motor on the module.

There are two wires, a Red and a Black one that connect to the motor. Find those two wires on the connector that plugs into the connector on the main board, apply power form a 9V battery to those wires, the motor should turn in one direction. than reverse the wires, and the motor should turn into the opposite direction. If it does you may have a bad component, either a diode or a power transistor (pretty common) on the H Bridge.

Let us know what you find