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Just picked up an SX-64 for $20

carlsson said:
Yes, anything that blocks sunlight. However I have been able to read unprotected EPROMs that have been inside a computer for 20-25 years. As long as no sunlight reaches the chip, I think a missing sticker is not a disaster although not preferrable neither.
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Even then I've heard that there's no real risk of erasure from just general sunlight exposure.
 
Tiberian Fiend said:
What function does it serve?
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The function of a UV erasable chip? So if it becomes corrupted it can be easily erased and reprogrammed.

Here is a modem that has a chip with the same kind of thing on it. Sorry, I didn't show under the sticker but that would mean putting a large flash directly to the window, so I didn't do that. The chip is labeled M27C1001-45XF1 (so far had zero luck looking that chip up)

http://picasaweb.google.com/nathan....ComputersAndClassicGaming#5502160314059808034
 
Tiberian Fiend said:
I meant for the SX-64 specifically. I've run the computer several times with the cover off and the sticker missing.
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My guess is it's a custom Kernal or BASIC ROM. You shouldn't have a problem with running it without a cover... it takes a very strong UV light placed inches away from the window for like 20 minutes to erase one completely.
 
Hi
I just got on this thread. One should understand the cause
of the fuse blowing. It is possible that the CRT has a cathode
to filament short. This might couple unexpected voltages to
the video circuits and blow things.
From what I understand, the video circuit is a traditional
circuit that just takes composite video from the CPU and
displays this on the CRT. These usually run from 12VDC.
!2V feed back on the video in would do interesting things to
the video source.
Dwight
 
Dwight Elvey said:
From what I understand, the video circuit is a traditional
circuit that just takes composite video from the CPU and
displays this on the CRT.
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Actually, the SX-64's little 5-inch built-in CRT displays S-video (luma/chroma), not composite. If you look at the schematic, the monitor has the separate Luma and Chroma video signals going to it.
 
It's printed on the PCB's, too, which are surprisingly well-labeled. I guess I'm just used to purposefully-arcane PC hardware.

P.S.--Geoff, check your PM inbox.
 
After a chip-swap from a donor breadbox (courtesy Geoff) my SX-64 is now working! Well, almost. I can't load anything because the "D" key doesn't work. A few other keys don't work, either. Is this keyboard built like a typical modern keyboard? Any tips for taking it apart?
 
Although I have never taken apart the SX keyboard, I suppose it is functionally identical to all other Commodore keyboards. In that case, the mechanism consists of a plastic pin with a graphite covered rubber plunger. This item touches a printed circuit board, and contact is made. Usually it is enough to take it apart, sweep the circuit board with a bit of isopropanol alcohol and reassemble. Sometimes you need a little graphite spray or something to re-coat the rubber.

Of course the fault could be elsewhere than in the keyboard. Check the cable so all pins still exist and look straight, not pushed a bit into the shell. Finally I suppose one of the 6526 CIA's might be partially faulty which causes a few keys to not respond. I recently damaged a 6522 VIA in one of my VIC-20's, and the net result was that some keys and combinations didn't register, while others did. You would need to look up schematics to tell which chip is which, but if you have 1-2 known good 6526 chips you could try replace them and see if it improves things.

But first, take apart the keyboard and try to clean the board.
 
Tiberian Fiend said:
After a chip-swap from a donor breadbox (courtesy Geoff) my SX-64 is now working! Well, almost. I can't load anything because the "D" key doesn't work. A few other keys don't work, either. Is this keyboard built like a typical modern keyboard? Any tips for taking it apart?
Click to expand...

Excellent! Glad it could be of some use. It's just been sitting around here for a while. Was the ROM in fact a JiffyDOS? I thought it was, but I wasn't sure when I sent it to you. Which chip was causing the problem?

As for the keyboard, carlsson is correct. Probably a bad key on the keyboard itself rather than a CIA. Usually multiple keys will be dead if a CIA is problematic.
 
Tiberian Fiend said:
After a chip-swap from a donor breadbox (courtesy Geoff) my SX-64 is now working! Well, almost. I can't load anything because the "D" key doesn't work. A few other keys don't work, either. Is this keyboard built like a typical modern keyboard? Any tips for taking it apart?
Click to expand...

The SX-64 keyboard actually uses a plastic sheet with a carbon pattern printed on it to make contact with the circuit board. Pop open the keyboard case with a screwdriver or your fingernails and take out all the screws securing the keyboard to the case. Then, pop the keys out from the back of the circuit board (you should see plastic tabs poking through). After that, you should be able to peel the plastic sheet up starting from the edge of the keyboard up until you get to the little metal bar that holds it in place. Do not remove that bar or peel past that point. If the function keys are giving you trouble as well, peel up from the other side of the keyboard until you reach the metal bar. Also, when peeling the sheet off, be careful of the rubber insulation layer that protects the carbon traces. It has some jagged edges that tend to get loose and stick to the circuit board, and these should all be flattened into their original positions before reassembling the keyboard. From there, it really is as simple as wiping the circuit board with alcohol. Just make sure it's dry before placing the plastic sheet back down. After that, you can push the keys back in place and reassemble. There might be a couple of screws I forgot to mention, so stay observant before you follow my directions exactly. :p
 
geoffm3 said:
Excellent! Glad it could be of some use. It's just been sitting around here for a while. Was the ROM in fact a JiffyDOS? I thought it was, but I wasn't sure when I sent it to you. Which chip was causing the problem?

As for the keyboard, carlsson is correct. Probably a bad key on the keyboard itself rather than a CIA. Usually multiple keys will be dead if a CIA is problematic.
Click to expand...

It did contain a JiffyDOS ROM. If I don't find a use for it, would you like ROM back? I swapped the entire chipset except the ROM; the SX-64 uses a completely different chip.

All of the contacts on they keyboard's PCB were shiny and clean when I opened it up. It looks like I'm stuck swapping CIA's until I can find a combination that works.
 
Maybe the plastic/carbon sheet is the problem? Try to press the "D" key by making contact directly on the PCB and see if the key responds.
 
Tiberian Fiend said:
It did contain a JiffyDOS ROM. If I don't find a use for it, would you like ROM back? I swapped the entire chipset except the ROM; the SX-64 uses a completely different chip.

All of the contacts on they keyboard's PCB were shiny and clean when I opened it up. It looks like I'm stuck swapping CIA's until I can find a combination that works.
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Nah, you can keep it. Maybe karma will pay me back later. ;)
 
The "D" key is working now, but it and a lot of other keys are mushy or require a lot of taps to produce a letter. They seem to be making poor contact, but I'm not sure I can get the contacts much cleaner than they already are.

When I tried loading a disk, I heard some crunching followed by a "file not found" message and the blinking light of doom. This means my drive is due for a re-alignment, yes?
 
Tiberian Fiend said:
The "D" key is working now, but it and a lot of other keys are mushy or require a lot of taps to produce a letter. They seem to be making poor contact, but I'm not sure I can get the contacts much cleaner than they already are.

When I tried loading a disk, I heard some crunching followed by a "file not found" message and the blinking light of doom. This means my drive is due for a re-alignment, yes?
Click to expand...

Try cleaning the heads first. No sense getting all the equipment required for a realignment when it could just be a dirty head.

And of course make sure you try more than one disk, since the disk could be bad as well.
 
jmetal is correct.

I always had very good luck with just an alignment disk/program made with a working drive and rotating the stepper until it was good. To do it right of course requires a factory calibrated disk and an o-scope.
 
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