You have to remove the right cover. Take out the encoder and belt tensioner. Remove the right plate. Move the carriage all the way out of the beam so you can access behind it. Redo everything.
Maybe I get something wrong, its like this in 300 but similar on yours
Hi everyone. Our belt on our HP L26500 printer began fraying so we halted printing. We have ordered and received a new belt but was wondering if anyone was able to guide us through how to install the new belt ourselves in the easiest way please? Many thanks.
Remove left cover also. Remove the encoder strip. Use this time to clean the encoder strip with alcohol. Clean the rails as well. You can use alcohol or something stronger. Do not forget to clean upper rail. Will be good idea to have around second man to push the encoder bolt when you remove the small encoder screw and when redo the encoder strip.
Be careful when removing and inserting the encoder into the carriage. If the encoder has come off on the right side, use tape to thread the strip into the carriage.
Install the belt exactly as the old belt was installed. It is in two parts and can be reversed.