Since the introduction of the 900 German Equatorial in late 1994, we have offered successive generations with improvements in both the mechanical construction and drive system. Since our design and production staff includes experienced CCD imagers, we are continually pushing the mounts to the limits of performance. Equally important, our customers have offered valuable feedback and suggestions throughout the years.

We are pleased to offer a variety of upgrades and spare parts so that you can obtain maximum performance from the 900 mount that you own. Some of these upgrades are available for all 900s and some are appropriate to particular models, but not others. Please check the product descriptions carefully to determine if a particular upgrade or component can be used with your mount. If you are confused by the HDA, QMD, SMD and GTO designations of the 900 mounts, please refer to a brief history of all 900 models. If you require a spare part not listed below, please do not hesitate to call.

For all previous model 900 mounts, we can upgrade the bearing system in the Dec axis to the present standard. This will allow full tracking and guiding with excellent precision in all mount orientations including upside down operation well past the zenith. In addition, we will add a spring-loaded bracket, modify the worm bearing support for more precise worm reversals and check out all guiding functions with our test equipment. List of things we will install:

• Add new thrust bearing to the Dec worm wheel
• Add preload system to shaft bearings
• Add spring-loaded motor box bracket
• Modify the worm bearing support and adjust preload
• Set all preloads to factory specifications
• Re-grease worm wheel and motor reduction gears
• Test the fully assembled Dec. axis for precise reversal motion

Should I upgrade my mount?: It is only when you are trying to control the mount to arc second position accuracies in declination that it becomes important to have this axis modified to the latest configuration. If you don't fit this profile, the upgrade is not necessary.

Mounts: All 900 mounts with serial number 900450 and earlier numbers, as well as 900501. Mount models include 900HDA, 900QMD, 900SMD and 900GTO models.

This upgrade is very time-consuming, so several mounts must be done at one time in order to be cost effective. Since we are providing this upgrade with no profit, we ask that you arrange to send your mount in according to our upgrade schedule. If you require that your mount be upgraded at a different time, there will be a surcharge.

Procedure for upgrade:

• Find the serial number of your mount. It is stamped on a metal plate that may be located on the inside of the polar forks or in one of the honeycomb cutouts where the RA and Dec axes connect (you have to take the mount apart).
• Call Astro-Physics to determine the next available date and obtain a Return Authorization number. You can book ahead into a future month on the schedule, if you wish.
• Send the dec axis to arrive between the dates specified below. We will begin the repair right after these dates, so it is important that all parts be here on time. If your dec axis is late, there may be a surcharge (to cover additional setup costs) or it may have to wait for another time. Be sure that you pack it well. We suggest that you wrap it in a thick layer of bubble wrap, particularly around the motor box area and put it in a box with packing material. Then, put that box in another larger box, again with packing material between the boxes. That will assure safe transport.
• Assuming that the process goes smoothly, we should be able to ship it in a week to 10 days (allow additional time for shipping). Please note that shipping and insurance charges are additional. We normally ship ground, so please let us know if you want it shipped by a faster service.

Upgrade Schedule.
The Dec axis MUST arrive between these dates so that we can update your mount during the full moon time, for your convenience. Please read the procedure above.

September 28 to October 4, 2011

This adapter fastens to the polar axis rear plate on the 900 mount, allowing use of our Right-Angle Polar Alignment Scope (RAPAS). The RAPAS can be used with all 900 mounts. This adapter is push/pull adjustable for precise alignment. Once adjusted, it will retain its precision, allowing the polar alignment scope to be removed and re-inserted as needed. Includes three replacement (longer) socket head cap screws. Please see this link for additional information.

Individuals who own the very earliest 900 mounts may want to consider upgrading to this more substantial altitude assembly. You may also consider purchasing just the Altitude Adjustor Brace (9ALBKIT) described below if you want to reuse the original Altitude Knob, Threaded Rod and other components, which are common to both designs. Installation instructions.

Includes: Our part # S900AA-A, four 1/4-20 x 5/8" flathead socket cap screws.

Mounts: All 900 mounts (HDA, QMD, SMD and GTO) that have been produced.
Note: This Heavy Duty Altitude Adjuster Upgrade is now included on all new 900GTO Mounts and does not need to be added to a new 900GTO purchase.

If you do not wish to replace the entire Altitude Adjuster Assembly with 9ALKIT above, you may wish to consider purchasing just the brace and installing the other original parts yourself. Installation instructions.

Includes: Our part # M9060-A and four 1/4-20 x 5/8" flathead socket cap screws.

Mounts: All 900 models (HDA, QMD, SMD and GTO) that have been produced.
Note: This Heavy Duty Altitude Adjuster Brace Upgrade is now included on all new 900GTO Mounts and does not need to be added to a new 900GTO purchase.

If you operate your mount remotely and are concerned about cables snagging on the RA clutch knobs, you may wish to remove them and substitute our modified set screws. Please do not attempt to install standard set screws, since they must be a particular length and profile to work properly. If you install the modified screws, you will have to use the 5/32" allen-head wrench from the set included with your mount to loosen and tighten them. Please tighten evenly with respect to the opposing clutch knob and do not over tighten. These set screws are only necessary for the side of the mount that has the cable. The normal clutch knobs will remain on the other side. Please note that each mount requires only 2 modified clutch set screws.

Mounts: All 900 mount models (DA, QMD, SMD and GTO) that have been produced.
Note: This is an optional item and is not included with new 900GTO purchases.

To reduce the possibility of a cable snag while operating your mount remotely, you may wish to remove one of the dovetail knobs that secure the Dec axis to the R.A. axis, and substitute it with our replacement assembly.  The assembly would only be needed for the side of the mount that has the cable.  The standard dovetail knob will remain on the other side.  You will only need to purchase one per mount.

Use the 3/16” allen-head wrench included with your mount to install and adjust tightness. Tighten to approximately the same tension as the corresponding knob on the other side.

WARNING: Do not over-tighten the knob replacement assembly!

Note that a small portion of the assembly will protrude from the side of the mount. This is normal and should not interfere with the mount cable during remote operation.

Please refer to the image at the right.

Engraving on the name plate has been changed to "Astro-Physics 900GTO Servo Drive". The original SMD (servo motor drive, but not go-to) and GTO (servo motor drive with go-to) versions of the mount shared the same name plate "Astro-Physics 900 Servo Drive". Note that the GTO designation was not there. We decided to more clearly identify the mount and offer the new name plates to prior GTO owners, as well. You will need two name plates, one for either side of the Dec. axis.

Mounts: 900GTO only. We will request the serial number of your mount when you order to ensure that this is the proper name plate for your mount.

If you are upgrading your 900GTO from the GTOCP1 Control Box, you will need this adapter kit. It features a dovetail attachment so that the GTOCP3 control box can be easily removed. Simply loosen the two thumbscrews and lift the control box from its position. We also provide two set screws if you prefer to use them.

Includes: Our part #s M9396-A, E0262, two 8-32 x 1/4" socket set screws, two 8-32 x 3/8" thumbscrews (to use in place of the set screws, if desired) and three 10-32 x 3/8" socket buttonhead screws.

Mounts: 900GTO only. We will request the serial number of your mount when you order to ensure that this adapter can be used with your mount.

This sight hole cover threads onto the back of all 900GTO mounts shipped since October 2005. One of these aluminum covers is included with all new mount purchases, but now they are available separately for anyone who needs one.

The rear of the 900GTO R.A. axis was redesigned in October 2005 to be slightly larger than the 1200s, 400s and earlier versions of 900s. This change resulted in the need for a larger diameter cover.