Authors

James Choate (jchoate@confusionresearchcenter.org) 1, 2

1. Confusion Research Center, Austin, TX. (http://confusionresearchcenter.org)
2. Central Texas Commodore User Group, Round Rock, TX. (http://www.meetup.com/Central-Texas-Commodore-Users-Group/)


Abstract

This document is intended as a collection of historical facts as well as current observations intended to help users of the Commodore SX-64 computer. This was an extremely popular variant of the best selling computer of all time, the Commodore 64. It is a transportable (approx. 28 lbs.) computer with built in floppy and CRT display. It also has a full compliment of ports, excluding the cassette port, allowing use of almost all standard accessories. This made it one of the more advanced computers for the mid 1980s that was available for home use. Within a basic skeleton describing how to take the machine apart and put it back together will be embedded descriptions of repair of failed parts as well as hardware upgrades.



Image Source: Bo Zimmerman

Introduction

This document describes the basic construction, operations, and theory behind the use and maintenance of the Commodore SX-64 computer. It's intended audience is anyone who has a SX-64 and wants to keep it in an operational state. It is expected this document will grow as existing documents are included as well as problems are identified and resolved. The primary focus of this document is specifics related to the hardware with software topics coming into play mainly in a supporting role. The primary skeleton of the document is the suggested dis-assembly/re-assembly steps. Embedded within this will be descriptions for repair and expansion of the system.

Required Tools

Initial Operations Test

The results of these tests will help determine which parts of this document apply to your computer issue.

General Notes


Top Cover Disassembly


Image Note: Always keep a hand on the machine when on the side or end, it is unstable and will fall over. The Floppy Disk Basket is removed in this image.

Bottom Cover Disassembly

Except for floppy disk allignment you won't need to remove the bottom cover usually.


Image Source: Bo Zimmerman

CRT Monitor Removal/Replacement

DANGER: The CRT has high voltages, hard vacuum, and some components are toxic if exposed. Wear safety glasses!

The CRT does not usually need to be removed from the chassis unless it is failed. While working on the floppy or the floppy disk basket you will need to loosen the monitor so that you can lift it up to gain access to the floppy related components.

Floppy Disk Basket Removal/Replacement

This is necessary to get to the retainer screws on the floppy tray blocking access to the top of the floppy drive.

Floppy Drive Cleaning

Unless you're having recurrent read/write errors the only routine maintenance needed is a dry or wet floppy head cleaning disk.

Assuming you have the computer open, and the floppy disk basket removed, you can lift the read/write head and clean it with a cotton swab and alcohol.

Floppy Drive Alignment

Floppy Drive Replacement

Floppies from a Commodore 1541 have a different cable harness than the native SX-64 floppies. They will work but a custom adapator cable must be built. Also, there are at least two different makes of floppies used in the SX-64, the cable harnesses should be identical.

Modifications


Image Info: The red button is the reset and the black button is the drive select.

Adding a Reset Switch

Adding a Drive Select Switch

Problems

Stripped Screw on Side Runner

This is what happens when you're tired and in a hurry :(

The first thing I tried was a small pair of channel lock pliers. My thought was to grab the head and pull out while rotating it counter-clockwise to un-screw it. Couldn't get a good grip on the head because it's round and the channel lock jaws just wouldn't get a good opposing grip position. Then I tried a screw removal tool. No joy there either. Even with the drill on low speed it just wouldn't get a grip. Finally, I get it out using a small pair of square flat jaw pliers. The screw actually came out pretty easily once I figured out how to get a grip. the screw threads were pretty much shot but the threading seems like I may be able to re-tap it.

Broken Cartridge Door


Image Notes: This is the underside of the cartridge port. Along the top edge of the hole you can just make out the spring and rod that would hold the missing cover.

Image Notes: The rod was slipped to the right, freeing the rod and spring. They were then removed and set aside.

Image Notes: Pay attention to the precise location of the spring, there are small bumps to help locate it correctly.

Image Notes: Slide the end with the spring in first, then position the door half so the rod will then go througg the mounting hole in the right. Then make sure the springs are positioned correctly and the door halves move freely. Finally, replace the two end covers to keep everything in place.

Reassembly

Simply execute the steps above in the reverse order. Be sure to not miss any screws!

Operations Test

Repeat the initial operations test (above) to verify the computer is still working as intended, then test any upgrades or other modifications. Make a note of these additional tests (and their results) so that they get included in future initial operations tests.

Acknowledgements

Disclaimers

Author Contributions

Disclosures

Appendix

Notes

Bibliography and References