Guiding error on a Skywatcher Adventurer 2i

We received a Skywatcher Adventurer 2i mount that exhibited significant guiding problems: during longer exposures, the stars exhibited pronounced, periodic streak-like images. The axis drifted significantly during tracking and could no longer be locked. PHD2 exhibited severe stops during tracking.

When checking the play of the RA drive, the problem immediately became apparent:

Video.

https://www.teleskop-spezialisten.de/shop/images/Reparaturen/StarAdvent2i.mp4

The following tools are required for the repair:

3.0 mm Allen key

2.5 mm Allen key

2.0 mm Allen key

Threadlock

Repair

To access the drive train, the worm gear must be removed:

Remove the clamp using 3.0 mm Allen screws.

2. The clamp of the RA axis is simply unscrewed.
   
    

3. Using a 2.5 mm Allen key, loosen the four screws holding the worm gear. The roller bearing can simply be left on the worm gear.
   
    

4. The worm gear is removed.
   
    

5. These two countersunk screws (3.0 Allen key) hold the drivetrain for the rear axle. They will also be removed.
   
    

6. Now you're holding the drivetrain in your hand. The two screw holes correspond to the screws you loosened in step 5. The small black grub screw for the center drive axle had come loose.
   
    

7. Here's a closer look at the grub screw (2.0 mm Allen key). It's hand-tightened. The main body is die-cast, which is quite soft.
   
    

8. The two countersunk screws are coated with screw locking compound and reinserted.
   
    

Reassembly is done in reverse order.

Afterward, the rear axle backlash was correct again.

Yours, Karsten