Restoration Project #1 – Atkelar’s SX-64

During a recent retro session I was thinking about my first experiences with computers back in the mid eighties. It.

During a recent retro session I was
thinking about my first experiences with computers back in the mid eighties. It
was with the computer my uncle and back then and I have tried for the longest
time to get my hands on one of those models but they usually go on eBay for
way too much money! But back home and also back in the present time I did a
quick search for it and behold: an affordable version was up
for “buy now”! The only potential issue with it was it is a US model and uses
110 volt 60 Hertz and NTSC while I would ideally have 240 volts 50 Hertz and PAL.
While I was waiting for it to arrive I read up on the hardware manuals and
check to see if a conversion was possible. The NTSC would not be much of a
problem as modern TVs can deal with it just fine but the power supply would
have to undergo extensive modifications. …and finally after a week of waiting it
arrived! behold the Commodore 64 “luggable” or SX-64
Executive as it was known. I’m afraid to say that the packaging was suboptimal:
the 10 kilogram computer was thrown into a box and one sheet of bubble wrap was
added – mostly for decoration I assume – amongst some newspaper pieces.
Needless to say it took some damage in the process.
I only realized the broken part of the keyboard case later. *sigh* The listing
also included the keyboard cable which has lost most of the time and a fast
load cartridge. Naturally the case was a bit scratched and everything was dusty,
but besides those minor issues it seemed nice of complete. Cleaning the case was done in an easy
fashion. Just gunk the plastic and aluminium parts into the sink scrub and
rinse. Then put up for drying and done! The next steps in my plan recapping that
sucker and modifying the power supply and giving it a good cleaning while it’s
open; oh boy there are lots of screws in that thing! To tackle the power supply I
checked and compared EU and US versions; not good… I would need different
rectifiers some caps and a transistor as well as a new primary transformer. The
latter one was a real showstopper. Time for Plan B! I did some searching and
found a power brick style power supply that would fit the required power output
and was only about a third of the original size. yay! I cleaned the PCBs and reseated the
chips along with some contact cleaning fluid. I did make sure that it was non
conductive before applying it to the sockets, yes. The investment for the desoldering iron
paid off nicely: I went through the capacitors like a breeze. The new ones
arrived after some waiting. After putting everything together and
connecting the new psu the big moment was finally here: would it power on? would
I get zapped by the 14kV CRT voltage? Tune in next week to find out Just kidding! Bummer! Let’s start the troubleshooting
process… at least the screen seems to work okay. Probing the individual pins of
one of the chips I realized that the outputs were at 2.4 volts DC: not good! It’s supposed to be TTL level signals
and getting 2.4 volt average would work but my scope showed plain DC… also the
chip got extremely hot after a few seconds of powering on. At last the pla
chip arrived and i put it in and still see an empty screen at least the logic
levels are up and running fine I suspect MPU you and hope that it’s not the VIC
chip. I took this opportunity to finally mount the power supply into the back
panel and add copious amounts of heat paste. I also added a hidden reset switch…
I decided that it’s time to plug it into the wall outlet… whoops that tripped the
GFI! Well right the primary heatsink is actually NOT grounded, but has one lead
of the rectified AC attached to it! I checked the keyboard by applying 5 volts
to the I/O board and trying out the shift lock key: no response.
I followed traces, measured voltages and conductivity to realize that one pin of
the 23 keyboard connections got loose on the plug inside the keyboard… guess which one Well that episode at least gave me an
excuse to finally not only clean the case but also the contacts of the
keyboard. I also decided to add some heat sinks to
the chips. I found fitting once but no clips to attach them; cutting out my own
it is then. Finally after a long process: turn on insert the death test
cartridge and watch the memory test succeed! I can now put the lid on and
have fun! …well so I thought. After putting the lid on the old issue of the
crackling speaker returned and the computer would eventually crash. During
assembly I noticed that the screws that hold the back panel are actually pushing
against the CPU board! So: snip snip and the shorter versions now have some
clearance and finally it works even with the attached cover! And to top it off:
decals! Time to put in one of my favorite games
of that era and try it out! I can’t believe I managed to find the original
floppy disk of it and it still works! I still have no idea how long that thing
will work but as long as it does: hooray for 80s computers! you

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