My new in box Commodore SX 64 has some issues.

[CompaqSniffer]

Just got a Commodore SX 64 today, and it looks relatively unused. I have opened it up, and the only dust in it is dust you would expect from being in an attic for 40 years.

I got the thing off marketplace for $300, which I'd say is pretty fair after testing it. It doesn't have the keyboard cable which isn't a big deal (I can easily make one), and when I turn it on the screen just displays a bunch of zeros and squares. I have done some reading and it could be the PLA? I'm not too familiar with commodore repair. As a bonus I got two atari 2600 controllers.

The story is that the couple I bought it from bought a house fairly recently and when they checked the attic this SX-64 was up there! What a crazy addition to get when buying a house. I guess I should try for older homes when I go house shopping eventually. Maybe I'll also find another elusive and rare retro computer?

What do you guys think I should do to fix this SX-64? And what category should I post this under the commodore section since there doesn't seem to be one there?



Btw I got this near Charleston SC which is notoriously humid, but despite that this 64 is super dry, the box is dry rotted from being in the attic all these years. The inside of the 64 is spotless, it's like they bought the machine in 84 and played it once then put it back in the box.

 

[ClassicHasClass]

https://www.pictorial64.com/ is always a good starting point if you can get a picture on the display. The PLA might cause that, but I lean a bit more to the CIA. Do you have a dead-test cartridge?

 

[CompaqSniffer]

https://www.pictorial64.com/ is always a good starting point if you can get a picture on the display. The PLA might cause that, but I lean a bit more to the CIA. Do you have a dead-test cartridge?

I do not have any cartridges, this is actually my first ever commodore computer. Is there a common component that can die from heat? this has been in a south Carolina attic for 40 years, the box was so dry rotted that it crumbled to dust when I grabbed it. It got so hot that all of the moisture was sapped out of it. It must have endured a constant 130 degrees over the summer. I would say the solder joints would be cracked from the heat but nothing happens when I whack the side of the computer or jostle it a little. I'll still reflow the joints sooner or later, but I don't think that's the issue yet.

 

[halfpress]

I restored my first and similarly obtained SX-64 a few months ago (bought it for $150 off a guy that got it in a blind storage unit auction). Had everything but the usually missing blue caps on the handle (which I 3D printed and you can barely tell).

In my case, I had to replace both the PLA (I had a PLAster on hand) and, of all things, the Kernal ROM (I rigged one up hacking a UV ROM with a self-made adapter... but better other options exist like OneROMs, etc). There are a lot of modern replacement options for both, so shouldn't be hard to obtain if you determine it's either (or both or others). Do note that the SX-64 Kernal ROM is unique in some ways, but a C64 version WILL work for most functionality and testing (I used one until I made that custom one I mentioned). Today I'd use a OneROM.

But, as mentioned above, do buy a dead test / diagnostics cart and kit with the various plug-in harnesses (which won't cover the keyboard on the SX-64). I learned in the process that the internal 1541 drive has to be unplugged to properly pass the PLA test (I think?) or you'll get a false fail unless you have the right version of the deadtest. Again, if you know it, you can work around it.

Also, I spent time recapping the monitor in hopes of improving its linearity. Made no difference and it was a GIGANTIC pain to do. Turns out, some amount of bowing is totally normal on those units. I have the peace of mind it's been done now, I guess... but had I known, I might not have suffered through the stress and hassle of it. Yours looks as good or better based on the one photo I see showing the screen active. Other advocate for replacing it with a tiny LCD and there are good examples online of the procedure. Unless and until mine were to totally die beyond repair, I've opted to keep it original (which is my tendency... I figure replica and emulator machines are where I want modern substitutes, but original machines I want to keep as original as I can reasonably manage... at least on key user-facing parts like CRTs and floppy drives).

Fun machines! Be curious to hear what you find as you work on it.

 

[ClassicHasClass]

What about the disk drive? What does that do when you turn it on?

If you (blindly) type POKE 53280,0 and press RETURN, does the border turn black?

The screenshot suggests the VIC-II is basically working, your Character ROM is working, and enough of the Kernal was able to execute to set up the display and screen colours. Those things probably wouldn't happen if the PLA were shot, so that's why I think this is more likely a problem with the CIA that controls the VIC-II's display bank. The other CIA handles the keyboard and disk drive, which is why I want to see if you can probe it. Switching the CIAs is a time-honoured trick for determining if one of them has a problem.

 

[CompaqSniffer]

What about the disk drive? What does that do when you turn it on?

If you (blindly) type POKE 53280,0 and press RETURN, does the border turn black?

The screenshot suggests the VIC-II is basically working, your Character ROM is working, and enough of the Kernal was able to execute to set up the display and screen colours. Those things probably wouldn't happen if the PLA were shot, so that's why I think this is more likely a problem with the CIA that controls the VIC-II's display bank. The other CIA handles the keyboard and disk drive, which is why I want to see if you can probe it. Switching the CIAs is a time-honoured trick for determining if one of them has a problem.

I am currently waiting on DB crimp connectors for making a keyboard cable, but I will try to do that when I make a new keyboard cable. Also it doesn't seem like the disk drive does anything last time I turned it on. I'll do it again tonight and see if it does anything but sit there.

If the CIA is bad, can I swap it from a commodore 64C? my university has a couple that aren't working. They might not mind if I just take most of the ICs from it. I don't know if the 64C is different in any way to the regular 64.

 

[ClassicHasClass]

When you turn the computer on, the disk drive should briefly spin up, the light briefly come on, and then stop.

Yes, it should be the same 6526 CIA. The 64C is functionally same as the 64 except for some possible chip consolidation and using some HMOS components. However, not all HMOS Commodore chips are drop-in replacements for NMOS ones, like the VIC-II or SID, because of different voltages.

However, if you're in there already, you could try swapping the two CIAs inside the SX-64 now (they're the same). If the symptoms change, you've likely found at least one of the problems.

 

[Istarian]

I got the thing off marketplace for $300, which I'd say is pretty fair after testing it. It doesn't have the keyboard cable which isn't a big deal (I can easily make one), and when I turn it on the screen just displays a bunch of zeros and squares. I have done some reading and it could be the PLA? I'm not too familiar with commodore repair. As a bonus I got two atari 2600 controllers.

I don't know about the zeros, but the "square" you refer to is actually a rectangle and probably the block graphic character.

I would say the solder joints would be cracked from the heat but nothing happens when I whack the side of the computer or jostle it a little. I'll still reflow the joints sooner or later, but I don't think that's the issue yet.

Solder joints don't crack just from getting (or being) hot, that kind of problem usually results from being subjected to thermal cycling (cold -> hot, hot -> cold). The more extreme the temperature range and the more rapid the rate of thermal cycling, the more likely you are to have serious problems. If you stuck it in a room that was always 130F with constant low-moderate humidity, that would be perfectly fine. I'd probably be more concerned about dried out electrolytic capacitors.

 

[CompaqSniffer]

When you turn the computer on, the disk drive should briefly spin up, the light briefly come on, and then stop.

Yes, it should be the same 6526 CIA. The 64C is functionally same as the 64 except for some possible chip consolidation and using some HMOS components. However, not all HMOS Commodore chips are drop-in replacements for NMOS ones, like the VIC-II or SID, because of different voltages.

However, if you're in there already, you could try swapping the two CIAs inside the SX-64 now (they're the same). If the symptoms change, you've likely found at least one of the problems.

The light does briefly come on for the drive when turned on.

Also, good and bad news is that every single 64C at my university works, so I can't salvage any IC from them. I literally went through and tested (I think 7) all of them. One of them I thought didn't work but I guess I didn't try it after the power supply broke. They have those massive epoxied bricks that go bad if you leave them plugged in.

There's at least one thing I can brag about not having to fix, and that is my keyboard is perfectly white, not even the space bar has a molecule of yellow staining

 

[halfpress]

Impressive number of working C64s there. And I'm intrigued as to why your university has them... ?

Also, do keep an eye out for bad RAM ICs. Another common problem.

 

[CompaqSniffer]

I don't know about the zeros, but the "square" you refer to is actually a rectangle and probably the block graphic character.



Solder joints don't crack just from getting (or being) hot, that kind of problem usually results from being subjected to thermal cycling (cold -> hot, hot -> cold). The more extreme the temperature range and the more rapid the rate of thermal cycling, the more likely you are to have serious problems. If you stuck it in a room that was always 130F with constant low-moderate humidity, that would be perfectly fine. I'd probably be more concerned about dried out electrolytic capacitors.

Yeah the boot screen is pretty consistent with what it displays, it seems like it is that exact same order of zeros and rectangle every time I turn it on. I also knew about the thermal cycling for solder joints, the weather has really wierd as of late down here. There have been some days where the temperatures have swung pretty dramatically. I also just check for cracks because I work on CRTs and arcade cabinets and there are a lot of old technicians "fixes" that I have had to fix.

As a side note, sometimes a joint can also not look cracked, but upon further tap it is. A good technique I have used in repairing any CRT is to just preemptively reflow the flyback pins, as that has fixed a few CRTs I couldn't find the issue with.

Impressive number of working C64s there. And I'm intrigued as to why your university has them... ?

Also, do keep an eye out for bad RAM ICs. Another common problem.

The 64Cs were used for the electronics class in place arduinos before they were even conceived. There's a few breakout boards that I think use the user port? They breakout into breadboard and you can do regular stuff with them like you can with an arduino like blink an LED.

I'll keep an eye out for those ram chips as well.