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Restoring a Commodore SX-64


Grimm1966

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A couple of years ago i traded an 1993 SGI computer for this SX-64, which was a pretty good deal for me.  I like SGIs, but I'm more interested in computers from the 80s.  Besides the condition of the computer, which is ok, I really liked that it still had it's keyboard, original keyboard cable, original manual, the CRT is working, and the computer appeared to at least boot. That is the good, I will list the bad later.  So I finally have some time to work on the machine, and will eventually have some questions, so I thought I would post my progress here.

 

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On to the bad...

 

Once I received the computer a quick check revealed several issues,

 

1) The trap door on the cartridge port was loose and flapping around.  (I have already fixed this by turning the spring around and now the trap doors work as they should)

2) One of the clips on the front face plate is broken. (this is going to be a difficult fix)

3) One of the handle detente/locks has it's pegs sheared off.  (not too sure what to do about this, the other one still works)

4) A lot of missing screws.

5) The keyboard has issues as they usually do.

6) One of the screws that holds the handle on to the machine is striped.

7) One of the clips on the keyboard doesn't work. (it appears to be missing a spring)

8 ) Screen text is garbled when the computer is booted.

 

I have taken the computer apart so I can start getting it back up and running, electrically that is.  

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When I first opened up the machine I heard some things inside that were rattling around.  I turned the computer over and shook it and about 6 screws and other parts fell out.  I figured that I shouldn't turn the machine on again until I have fully looked at the guts. 

 

I watched a bunch of YouTube videos on the SX-64 and how to fix it.  Then I temporarily set the CPU and interface boards up with the CRT and the power supply on my desk so I could get it working before I started looking at the physical issues.  The garbled text was caused by a bad character ROM, which I have some extras of, so I replaced it with one of my good ones.   This fixed the text and the computer appears to be working ok.  I ran a diagnosis with the deadtest cart and it appears to be working, at least from what the cart shows.  

 

Those of you who are eagle eyed, will have noticed that the colors are off.  The kernal ROM was replaced with a Commodore 64 ROM at some point and the date code on the installed chip is 8519 (MCM 68769P30).  Instead of searching for an original ROM, which is probably unobtainium now, I decided to go with the JiffyDos ROM which will be a good upgrade anyway.  Some of the things that were rattling around inside was the plastic rail that the interface board gets inserted into and the screws for it.  So I was able to get it reattached to the computer's frame (very happy about that).  The PLA was also replaced at some point (date code: 8721) and is a Signetics chip so it should be higher quality?  

 

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I did plug the floppy drive in and tested it.  The red light came on and turned off after a second which is good.  I wasn't able to test it any farther because the keyboard needs some TLC.  I will test it again when I get the keyboard in working order.  I have cleaned the drive and lubed the rails. 

 

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Next I thought that getting the keyboard would be the next best step.  The keyboard is grubby and needs to be cleaned.  I was worried that someone had been inside the keyboard before me like the computer.

 

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Here is the broken clip.  It doesn't have any physical damage that I can see, but it just moves loosely in it's slot.

 

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I popped the keyboard bezel off which was really hard, I ended up having to use a metal tool as the plastic one wasn't strong enough.  Thankfully I didn't damage the plastic any.  It doesn't appear that anyone else wad inside the keyboard as all of the screws did a pop as I unscrewed them.  I'm pretty sure that this computer was dropped onto the floor or something as that is the only thing I can think of that would cause the damage I'm seeing here.

 

Once I opened the keyboard I saw what had caused the clip to slip around.  The part of the keyboard that holds the clip spring was broken off.

 

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This should glue back on pretty easily I think.   I also noticed that one of the registration nubs for the part that retains the clip is broken off.  One of the nubs that registers the keyboard PCB is broken as well.  And one of the clips that holds the bezel onto the bottom of the keyboard is broken off too.

 

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I did find the broken off piece as it had became attached to the foam tape that is used to secure the keyboard wires.  This is going to be a tricky one.  If I just glue it back on, it will not be strong enough to hold.  Does anyone have a recommendation or some experience with this?  I was thinking of using epoxy or super glue/baking soda to build up the back of the clip and give it some more strength?  I was worried that it would be too stiff to work then?  

Edited by Grimm1966
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While I'm thinking about what to do with the broken pieces of the keyboard, I started cleaning and fixing the keys themselves.  Removing the keys is easy, I have just been using a small screwdriver and depressing the tabs on the switches and pushing them through the PCB.  I then very carefully lifted the membrane from the PCB and used a plastic spudger to scrape the parts of the membrane that stuck to the PCB.  Sometimes I had to use quite a bit of force to get it to unstick.  

 

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I DID NOT remove the metal bar shown here that keeps the membrane carbon connections attached to the PCB.  From what I have seen, if you remove the bar and pull the membrane from the PCB, it's really hard to get it to make connections again and can destroy the membrane.  The keyboard still worked for the most part, so I didn't think that I needed a new membrane, although you can purchase them new.  

 

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Here is the membrane lifted up so you can see the carbon contacts and the white rubber layer that gets stuck to the PCB.  I cleaned the carbon contacts with a dry Q-Tip and cleaned the PCB contacts with IPA. 

 

Most of the issues with the keys happened to be with the small springs in the switch.  How these switches work is that they have two springs, one pushes the key up, and the other center spring that pushes the two contacts on the membrane/PCB together when the key is pressed.  This second spring is the problem in that over time and use it can get compressed.  Once that happens there are two problems that it causes.  One, the key will not register a key press, or you have to really slam the key down to get it to register.  The other issue is that it can cause the key press to bounce and register several key presses.  Here are three key switches that demonstrate the issues. 

 

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The first key I adjusted too much, so it sits proud of the black plastic switch housing.  This can cause a key to look like it's pressed all the time or to register when you are typing keys next to it, etc. The second key shows the spring flush with the housing which is correct.  The last key shows an example of a compressed spring that is too short to work correctly.  It's really easy to over stretch the springs and you should adjust them little by little and not try to get it the right length on the first try.  Compressing them back down is a lot more difficult than stretching them out.  

 

No one has an opinion on gluing the clip back on to the bezel?  I still need to clean some strapping tape residue off of the bottom and bezel before I start to glue the bits and pieces back on.  

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While I had the key switches off I cleaned the key caps, which was a real tedious procedure.  I didn't want to just throw them all into some soapy water and wash them en-mass.  If I did that I thought that the water would get inside the switch housing and maybe corrode the springs.  So I cleaned each key by hand, all five sides.  :)

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  • 3 weeks later...

Now that the holidays are over I have some more time to finish up the keyboard.  Getting the remains of the strapping tape off of the keyboard was very difficult (it must have been on there for a very long time).  I usually use some WD-40, but it didn't work in this case and I had to carefully use a flat-bladed screwdriver to get the bulk of it off.  Then I followed up with the WD-40 to finish it and a good soap and water scrub.   

 

I used some super-glue to reattach the broken parts of the keyboard case and re-enforced them with epoxy.  Here is how the clip on the bezel looks after gluing it back on and putting the epoxy on the back of the clip.

 

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Hopefully it will be strong enough to survive, although I'm going to wait another 24 hours to try it out just to make sure that it's fully cured.  Here is the current state of the keyboard and system...

 

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I have fixed all of the keys that I found were not working correctly.  Again hopefully I will not have to open the keyboard back up to fix any of the keys.  Next up is the floppy drive and see if it works.

 

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I was able to finish the keyboard and the clip that I re-enforced with epoxy worked really well.  In fact the bezel snapped into place so firmly, I'm not sure how easy it will be to get it back off if needed.  

 

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I tested the floppy drive as well and it appears to work and have no issues.  Having Jiffy-Dos installed really does make reading disk so much faster.  :)  This SX-64 was manufactured late in the game (early 1984) so it has some modifications to make the computer easier to work on.  The floppy drive has two brackets on it that allow the drive and the storage compartment to be lifted straight up and out of the machine.  There are four screws that need to be removed to release the drive that are accessible from the top.  So on this computer you don't need to remove the main PCB or the CRT to get at the screws.  I have drawn red arrows to where the screws go. 

 

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Next is to get the Ultimate Reset installed and hooked up.  I'm going to attempt to make it easy to unhook it if I need to take the computer apart again.  

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  • 1 month later...

Sorry I haven't been updating this thread lately.  I'm at the point now where I need to figure out how I'm going to install the Ultra Reset (I keep calling it the Ultimate Reset) and to fix the stripped out handle mounting screw.

 

I want to be able to completely unhook the reset board from the system so I can disassemble the system if needed in the future.  In the recommended installation most of the connections are soldered in, which is fine, but I would like to have an easier method.  One way to do it is to solder the connections to the reset board and have pins and sockets for the other ends.  This works well for some of the connections (power) but not others (system reset).  Another way would be to turn it all around and solder the connections on the system side and then have pins and sockets on the reset board.  I'm kind of leaning towards the second method, unless anyone has a better idea?  

 

The stripped screw is tricky as well.  In this case there are again several ways to solve it.  I'm leaning towards drilling the stripped screw hole out and putting in a bushing to fix it.  I have the tools to do this (lathe) and the material (360 Brass bar) to make the bushing.  Once made, I would glue the bushing in with Locktight and call it good.  Also I have purchased the correct (I think) drill and tap (M3 X .7) to put the threads in to the bushing.

 

The problems with this is that the handle screws have a shoulder on them.  The function of this shoulder is that when you tighten the screw, the shoulder contacts the frame of the computer and helps with handling the side forces from the handle.  The difference between the diameter of the screw threads and the edges of the shoulder is very small.  If I drill out the hole larger than the shoulder it would just be making contact with the bushing and will be much weaker and more prone to tilt in the new larger hole (it would have a tendency to tilt the bushing in this case).  My plan is to drill out the stripped hole to a size between the shoulder and the threads and hope I have enough material so I can turn down the part of the bushing that will fit into the hole with out compromising the threads that I will tap into it?  It doesn't help when the shoulder has a rounded edge on it.  In the end I hope to have the shoulder still contact the frame and have enough material to put in the threads too. I'm also planning on having the bushing's outside diameter to be much larger than the screw shoulder to give it some more support. 

 

Edited by Grimm1966
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On 2/10/2024 at 3:16 AM, Papalapa said:

Good job, please continue posting when news are available 😀

Thank you, I'm still working on it and will have a new post here soon.  I'm just working through how I'm going to install the Ultrareset board and connections.  I have a plan so we will see how it works out.  :)

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