James Choate (email@example.com) 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/)
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
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.
- Workspace of approx. 3ft. x 3ft. in size
- Good lighting
- Safety Glasses
- Power Strip (approx. six outlets)
- Plastic Parts Tray
- Commodore Floppy Alignment Disk
- Screwdriver Set. It should include an extension or have several long shaft drivers. A hex bit set is acceptable.
- Hex Driver with assorted bits. The driver needs to work like a rachet, holding the bits perpendicular to the driver handle.
- Small Pliers Set, at least a long nose and side cutters.
- Magnifying Glass or Loupe
- Permanent Marker
- Plastic ruler (6"), compass, and right triangles (30-60-90 and 45-90-45)
- Small Tie Wraps
- Cotton Swabs
- LockTite or other security product (e.g. plastic model paint or fingernail polish - usually not needed, used to secure screws and other mechanical components once aligned)
- Epoxy Glue
- Super Glue
- Silicon Lubricant (try and avoid machine oils)
- Floppy Drive Belt (usually not needed)
- Floppy Head Felt Pad (usually not needed)
- Hot Glue Gun and glue sticks
- Soldering Iron, solder, de-soldering tool
- Dremel or similar tool w/ accessories
- Electric Drill w/ selectable torquel limiting clutch, battery powered if available
Initial Operations Test
- Verify the machine powers up and gives a correct display.
- Verify if the keyboard works.
- Verify the internal floppy drive will reset via the front panel reset button.
- Insert and run a floppy drive alignment test program, if available.
- Insert a known good floppy and attempt to load and run a program.
- Run a simple program and save it to floppy. Try and load it on another computer if possible.
- Insert a known good cartridge (with power off!) and verify it works.
- If you have a game disk and joysticks, connect the joysticks (with power off!) and attempt to load and play the game.
- If you have a modem and terminal program disk, connect the modem (with the power off!) and attempt to load and use the terminal program.
- As the various screws are removed place them in the plastic parts tray, in some sort of order, to keep track of them.
- Be very careful when handling the monitor, it has very high internal voltages that can be lethal. Avoid putting body parts into it's internal spaces.
Top Cover Disassembly
- Position the SX-64 such that you are looking at the rear.
- On the right and left you will see two pair of small screws (A) in the middle. They hold the two access covers on (one on each side), remove the screws.
- Slide the two access covers toward the rear and remove completely, lay aside. Be careful as they are fragile!
- On the top rear corners you will see a screw (B), remove it and place both in the tray.
- Along each side you will see three small screws holding the top panel. Remove them and place them in the tray (all six, three on each side).
- At this point you can remove the top cover, lift from the rear and slide to the rear. Set aside.
Image Source: gkweb.net
Image Notes: A - 2 screws on each side hold the fragile side covers in place. B - 2 screws, 1 on each side help secure the top cover. C - 2 screws 1 on each side help secure the power supply and bottom cover.
Image Notes: The part of the slide that is sticking out in the air should not be pulled, pushed on, or bent.
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
- Look between the floppy basket and flopp drive (they're stacked on top of each other) and the CRT. About the middle of the machine you will see a screw. Remove it.
- At the bottom two rear corners you will see two screws (C). Remove them, but don't put them aside. Be careful, the power supply is heavy and it could damage the connectors or wiring.
- On each side you will see another set of three retainer screws, remove them and put them aside.
- You should be able to remove the bottem cover at this point.
- Replace the two screws on the back rear corners so the power supply won't be left loose.
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.
- At each corner of the CRT assembly you will see four screws, remove them. This is all that holds the CRT down.
- Lift the CRT from the front corners. As it comes up slide it forward so that it sits on the top of the front bezel. Always keep at least one hand on the chassis to keep it from sliding or falling back into the computer.
- To replace the CRT simply slide it backward and let the front return to it's original position. Look at the four screw holes to ensure it's back in it's correct position. Replace the four screws.
- If you are replacing the CRT itself, once the four screws are out, disconnect all the cables. Remember there is high voltage and hard vacuum in this device, it is dangerous, treat it with courtesy!
- Lift the disconnected CRT chassis out of the computer and place the replacement unit in its place. Reconnect the cables and replace the four screws.
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.
- As described in the first part of the CRT Monitor Removal/Replacement section, the monitor should be propped up and resting on the front bezel. Be sure to keep a hand on it, or otherwise secure it from dropping back into the computer.
- The floppy disk basket has two retainer screws toward the side front and two pins fitting into chassis holes that keep it into place at the side rear.
- Remove the two front retaining screw on the floppy basket. You'll need a long shaft screwdriver for the screw near the CRT and the hex driver for the other one.
- Once both are out, return the CRT to it's normal position and secure it with at lest two screws.
- Pry out on the chassis mount points and free the two retainer posts. The floppy disk basket should lift out of the way giving access to the floppy. Light pressure with your fingers or a flat blade screwdriver should be sufficient.
- Once any floppy related work is completed it's time to replace the floppy disk basket. Prop the CRT on the front bezel as before, be sure to secure it!
- Put the floppy disk basket back in the computer, put the two rear retainer tabs back in their holes. Simple finger pressure should be sufficient.
- Replace the two side front screws. Then replace the CRT.
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.
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
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.
Simply execute the steps above in the reverse order. Be sure to not miss any screws!
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.
Bibliography and References