Repair of a Celestron C9 1/4'' - Mirror mount & shell breakage

Product Description
Problem:
When the Celestron C9.25 telescope arrived for repair, the problem seemed manageable: The only thing that needed to be done was to reattach the secondary mirror mount, which had become loose.
After the usual initial general condition inspection, several problems came to light that prevented the telescope from displaying the expected image:

The secondary mirror mount is also designed to hold a camera. To ensure that this mount stays securely in place but at the same time does not exert tension on the Schmidt plate, it usually has a retaining ring, which was missing here.

The Schmidt plate and the secondary mirror had smudges.

After removing the Schmidt plate mount, a conch fracture became visible, causing unwanted light reflections.

The Schmidt plate and secondary mirror were no longer in their original, correct position.


Solution & Procedure:
In the first step, the Schmidt plate was removed from the mount and inspected for further irregularities.

The second pass proved quite difficult, as the secondary mirror mount wouldn't separate from the plate, which is normally achieved by simply loosening the screw connection. Only the application of heat loosened the plastic screw connection. Extreme caution is required here. Mechanical impacts must be avoided at all costs to avoid damaging the Schmidt plate.
Please never clean the mirror and plate with commercially available cleaners or cloths, as this will cause scratches and damage the coated surface!!!

In the third pass, the secondary mirror and Schmidt plate were properly cleaned first.
Since safety rings for this C9 mirror mount are not available for purchase and standard rubber rings do not meet the requirements, you have to get creative and make one yourself in the fourth pass. Soft rubber pads from hardware stores are best (they come in different thicknesses and degrees of hardness - you'll have to search a bit).
Teflon strips were applied to center the Schmidt plate; they are thin enough, yet durable and long-lasting, and retain their shape (!).

In the fifth round, the conchoidal fractures on the Schmidt plate were blackened. Even if they are located at the edge, they can cause unwanted reflections under certain light conditions.

In the sixth round, the focus was on the correct position of the Schmidt plate and the secondary mirror relative to each other and in the tube mount. Markings on all three parts often indicate the position: The Schmidt plate is usually at 3 o'clock, the secondary mirror at 5 o'clock.
With older Celestron telescopes, the correct position is crucial for a correct image!

In the seventh round, after correct assembly, the telescope was correctly aligned to the artificial star and finally checked using test images.

A word about cleaning the Schmidt plate:
A Schmidt plate rarely needs to be cleaned. Dust particles or small streaks do not affect the optics!
The glass surface of the record is coated! This coating reacts sensitively to mechanical and chemical stress.
We only clean Schmidt records in exceptional cases!
If you absolutely must clean the record, please observe the following points to avoid causing permanent damage:

Do not allow (skin) oils or acids to come into contact with the record - wear gloves,

Human skin is a carrier of oils and acids!

Never use household cleaning products - no glass cleaners, dish soap, or similar.

Use Optical Wonder and a microfiber cloth (lint-free).

Do not apply pressure to the record.

Never wipe particles away, always blow them away.

Do not blow with your mouth, only with a blower.

Pay attention to markings and retaining plates, ensuring they are returned to their original position.