Adventures in retrocomputing: Restoring a vintage Commodore 64.

20 May 2020

You've probably been wondering where I've been since my last update in the latter half of April.  I mean, where would I reasonably go right now when most of the country is locked down and only a relatively small number of people with more memes running inside their heads than conscious processes are running around with mall ninja gear and weapons (some props, most unfortunately not) doing their damndest to cut the population by infecting everyone around them with covid-19?  Well.. when I haven't been working (as one does) I've been reconditioning my old Commodore-64 computer, the first computer I ever used as a kid.  I've been carrying it around with me just about everywhere I've moved but it's only recently that I've had the time to really do any messing around with it (for obvious reasons).  It has been a learning experience if nothing else, because much of my knowledge of how to do stuff on a 40 year old computer has faded and been overwritten as technology has progressed.  It's also given me a lot of appreciation for how much things have changed for the better since the days of LOAD "$",8 and LIST.  Computers may not come with their own programming languages anymore, but the ones we have are significantly more featureful, significantly cheaper (I vaguely recall seeing an advertisement for a C compiler in 1986 for the Commodore 64 for the low, low price of $275us or therabouts), and way more accessible thanks to the Web and open source software.

This was not a quick process. I worked on this project in my spare time, in between working from home, going on supply runs for my family (and decontaminating afterward), taking care of stuff around the house, and waiting for orders of components, cleaning materials, and sundry things to arrive so I could proceed.  What with supply lines being all screwed up by the coronavirus quarantine, sometimes an order from Los Angeles would take two weeks to get to northern California but an order from Massachusetts would show up two days later due to unexpected overnight shipping.  It was also a labor of considerable monetary investment; I think my parents bought my C64 for something like $500us back in 1984.ev, and I easily sank that much money over the course of a couple of weeks into this effort.  Not that it's been in vain.

The first thing I had to do was clean everything up.  40 years of use, dust, and gunk can wreak havoc on any kind of electronics and I figured that I'd have my work cut out for me.  The first step, and arguably the most fun was taking the whole thing apart layer by layer.  I used old pill bottles and some tiny test tubes to sort all of the screws by purpose (hold the case together, hold the keyboard on, hold the keyboard together, and so forth) to make it easier to put everything back together later.  I also took copious photographs every step of the way, of which I will put up a gallery a little bit later.  It never hurts to know how things were put together before you started messing with them, right?  Working on the keyboard involved dismantling it into its constituent layers.  Popping all of the keys off required just a flathead screwdriver inserted under the key and using the shaft of same to pop them loose like a lever.  The springs and screws I soaked in vinegar for 24 hours to dissolve the rust; only one spring was rusted enough to break but that was near one of the ends, so it wasn't as bad as it could have been.  The sheer amount of crap under the keys, however, was nothing short of hair raising.  A can of compressed air didn't really accomplish much.  I wound up putting the plastic body of the keyboard into the kitchen sink and working it over with dishwashing detergent and a pot scrubber to remove decades of cat hair, dust, dry skin, and crumbs.  The keys went into baggies full of warm water and hand soap overnight, agitated every two or three hours to get most of the gunk loose.  Afterward I scrubbed them in the sink with an old toothbrush to get them looking nice again.

I ran some basic diagnostics on the circuit board part of the keyboard while I had everything apart.  Old printed circuit boards can be somewhat dodgy, depending on how well they were cared for, how they were stored, and how much abuse they've seen but I try to take good care of things so it wasn't as bad as it could have been.  I took some laboratory grade isopropyl alcohol to it, scrubbed it with another toothbrush (buy handfuls of crappy ones at the dollar store and you'll never be hurting for scrub brushes), and let it air dry.  I broke out my multitester, set it for continuity mode, and poked around on the board to test the connections between the cable and each contact point.  Everything was still in good shape, and the little conductive plungers that the keys sit on top of were all in good shape.  I probably should have re-taped the keyboard's cable connections but I wanted to make sure that the keyboard was still functional before I enacted any more "pain in the ass to undo" protocols than necessary.

The 64's RF shielding layers were pretty badly corroded.  It took some unsoldering of contact points as well as the removal of a couple of screws to get them apart for examination.  The years took their toll and patches of rust had bloomed all over the panels, both outside (exposed to air) and inside (facing the circuitry).  The nonconductive layer of cardboard between the lower RF shield and the underside of the motherboard was in reasonably good shape so I didn't have to cut a replacement insulator out of cardboard.  Scrubbing the aluminum shields down with hot water and soap, then alcohol, then an abrasive paste of baking soda and water (thanks, 8-Bit Guy!) was enough to remove the rust but left discolored spots behind.  There's not much I can do about that other than take a Dremel polishing wheel to them at some point, but I don't see a point to doing so just yet because they're still electrically sound and not visible during ordinary use.

The Commodore mainboard was also in fairly good shape.  I gave it the isopropyl scrubdown and then went over it with a jeweler's loupe and a good penlight.  The PC board was in good shape, better without the crap, and the connections were in good shape.  Out of an abundance of caution I decided to recap the board, or replace all of the electrolytic capacitors with modern equivalents.  Due to the fact that electrolytic caps are wet components, or are filled with a conducting liquid or gel they have a finite lifespan.  Sometimes they die early (remember the spate of exploding motherboard caps about ten years ago?), sometimes they die later (say, after 30 or 40 years), but no matter what they die explosively.  This is a common enough phenomenon in the retrocomputing community that it's fairly easy to get entire kits of replacement capacitors for different computers and disk drives, and even different revisions of same.  After doing some research I placed an order to for compatible recap kits for my Commodore's particular motherboard (assembly 250425), the RF modulator (the daughterboard which generates TV compatible output if you don't have a 'real' display), and my 1541 floppy drive (which took some reverse engineering to determine what I needed - more on that later).

While waiting for the recap kits to arrive I sent Argus prowling around the Net searching for the original C64 and 1541 service manuals from Commodore because they not only have diagnostic instructions but also the schematics and parts lists for each model.  From those schematics I could figure out where those replacement capacitors went in and how.  I also killed some time by testing the power supply to make sure that it wouldn't go berserk and fry every chip in my '64.  I did this with a multimeter, a jerry rigged way to hold the plug upright with some zip ties and a third hand, and this page at the C64 wiki.  As it happens, the business end of my particular PSU has only four pins, so that made life significantly easier.  Two carry 9 volts AC, and two carry 5 volts DC.  The respective pins are right next to each other so very little actual poking was required.  The voltages were well within expected limits so I didn't forsee any immediate trouble.  However, just to see if I could do it I decided to build a new power supply along the same lines as Perifractic's out of some parts around my workshop.  This wound up being an exercise in frustration.  The recommended project box is just not large enough regardless of how much cutting, grinding, and swearing I do.  Trying to solder the pins on a DIN connector is difficult enough, and trying to do so on cheaply manufactured ones that aren't even machined right is next to impossible.  I wound up sourcing a cable with compatible connectors on both ends, cutting it in half, and soldering to those wires but that doesn't seem to be working, either.  I'll probably revisit this particular problem in the future but right now I don't forsee a need to.

When the recap kits arrived I spent a couple of hours poring over the printed out maintenance schematics (they're much easier to scribble notes on than PDF files) and matching up which capacitors went where.  One desk lamp was repurposed as a through-board illuminator (so I could put a finger on top of one component, hold the mainboard up to the light, and see where the shadow of my finger ended) to figure out which solder pads I needed to work on.  After thirty years I finally figured out how to use desoldering braid: Heat up the solder until it melts; add a bit more solder if necessary to kickstart the process.  Make sure the desoldering braid is flat and the business end is even.  Touch the business end to the molten solder and watch capillary action suck it up.  Clip off the used part of the desoldering braid and repeat as necessary.  Just laying the desoldering braid on top of the connection and heating it up through the 'braid is not a good way to do it.

Maybe I'll record it and throw the video up on someday.

The recapping process barely took an afternoon.  Locate capacitor, note polarity, desolder, insert replacement capacitor, solder, clip off leads.  If you organize everything before you start soldering the task is significantly faster and easier than it otherwise would be.  While I was at it, I also decided to remove and recap the RF modulator.  If they sell recap kits for them, it makes sense to take care of that part at the same time while you have everything apart, right?  Plus, while there are folks out there who removed the RF modulators entirely and replaced them with something different, I didn't quite want to go down that road yet so I didn't actually do any research on that topic.  I didn't plan on it unless I had to.

As it turned out, it was a battle to unsolder the RF modulator so that I could pull it off and expose the underside.  The large solder points that connect the RF modulator's steel casing to the C64's ground plane were so well done that I had to throw most of a spool of desoldering braid, a couple of hours of work with a solder sucker, and some creative application of hemostats and pliers at it to pop the modulator loose.  And then there was the matter of figuring out which solder pads corresponded to the capacitors in that cramped little space... amazingly I had only one miss, and that was easy to re-solder.

I didn't mention cleaning up the case earlier because it was almost anticlimactic.  I scrubbed it down in the kitchen sink with dish soap and a sponge and let it dry overnight.  I thought I did a fairly good job but there are still scuffs here and there that seemed to come out while wet but didn't.  I plan on trying a melamine sponge on the scuffs once they're more widely available again.  While the plastic cases are somewhat discolored due to age I don't plan on retrobriting them just yet due to how tricky it is to source some essential components of the process right now.  I did spend a goodly amount of time using compressed air to remove a number of mummified house spiders that had taken up residence inside the expansion port at some point in the distant past.

Pretty much the same process was applied to my 1541 disk drive.  You can't do much with a computer unless you have some way of storing and retrieving data, right?  Restoring it took a bit more work than the C64 did.  As luck would have it my drive is sort of a transitional model: The drive mechanism itself is an Alps model, which means that it has the "push down and pull out/push in and up" latch on the front and not the rotating latch.  However, the drive's motherboard (Commodore disk drives were fully programmable computers in their own right, that's how a lot of their copy protection schemes worked) is indicative of the later revisions used in the 1541C disk drive.  End result: A little more care was needed when picking out the recap kit.  After scrubbing off and examining the drive's motherboard, I added the 4700uF and 6800uF axial caps to the baseline kit at Console5.  I also picked up a new drive belt for the motor because 40 year old rubber bands aren't known for their strength.  More isopropyl alcohol and antistatic swabs were used to clean up the drive's internals and remove the remains of a fossilized spider's nest from the drive's read/write head... Of such things are nightmares spawned.

I may as well cut to the chase: See that big-ass 6800uF capacitor?  I accidentally soldered it in backwards when I replaced it.  When I reconnected everything, plugged the drive in, and gave it a bench test... well, I didn't know exactly what I was expecting.  The power LED broke during removal so I couldn't tell what it was showing at the time.  The red "busy" LED was on long enough for the drive to POST and then shut off, which was expected.  A few cautious sniffs of the air smelled strangely hot and chemical.  Leftover alcohol?  No, couldn't be, that evaporated a week before.  Cooking dust?  Couldn't be that, either, I'd gone over the drive with compressed air, alcohol, antistatic swabs, a sponge...

On a hunch I paused the music I had playing and began touching each electrical component with a fingertip.  All of the chips were relatively cool.  The new capacitors were okay, okay, o-oh!

I nearly burned myself on the 6800uF cap.  I then heard something not unlike simmering, which is not a sound one should hear when electronics are involved.  I yanked the power cord as fast as I could, because reaching for the power switch would have put my off-hand closer to a cap about to blow than I was comfortable with.  As it turned out, the electrolyte guts of that brand new cap were boiling because electricity was going the wrong way through it.  The cylinder had swollen such that one end was convex instead of concave and it had levered itself up off of the circuit board.  If I hadn't caught the mistake when I did I'm fairly sure that the capacitor would have exploded while I was sitting less than a foot away from it.

Cue another order from Console5.  While I was waiting, I removed the tiny motor controller board from the bottom of the drive mechanism (the mechanical bit that you slide a floppy diskette - remember those?) and replaced the three capacitors on that with the three leftover parts from the original recap kit.  Jump forward another couple of days and I swapped out my mistake with a brand new capacitor which was oriented correctly (which is to say, it matches the polarity markings silkscreened on the mainboard).  A two hour smoke test (heh) on the workbench produced no nasty surprises, no magick smoke, no second degrees burns, and no explosions.  I cautiously connected the drive to my C64, powered everything up, and ran through everything on the 1541 demo disk.  To my relief and slight surprise, the drive worked as expected, which is to say that it worked.  So, I picked some old floppies out of my collection (yes, I brought my disks with me, too) and booted some old BASIC games that I'd typed in as a kid.  Again, those worked as expected (though I still lost at Nim because I didn't bother to mod the code to give me an advantage).  I also poked around with some educational software that I'd been gifted as a kid.  It too, worked.

You're probably wondering how I was able to see anything from my C64, which is a reasonable question to ask in light of the fact that I don't have a Commodore monitor anymore, and it's not as if I can just screw an RF modulator box onto the antenna lugs of a flatpanel television manufactured in 2015... after contacting a couple of knowledgeable folks in the retro scene, I ordered a RetroTINK 2X-Classic, which is a small microcomputer in its own right (a dedicated signal processor, really) that takes the component signal feed from my Commodore and processes it into HDMI, which my television uses primarily.  Due to the fact that my original component video cable is somewhere in my mom's basement (hey, you try sorting through a box of cables the size of an engine block when you've got 12 hours to get on the road when you're in the middle of a move) I ordered a replacement from 8 Bit Classics that works as well as I seem to remember.  The component cable goes into my C64 and plugs into the three jacks on the RetroTINK, and then the RetroTINK plugs into my television (I swapped out my Retropie to use its USB power supply and already plugged in HDMI cable).

I do have one concern right now, which is that sometimes it takes a couple of tries for my C64 to boot up to the BASIC entry screen.  Sometimes it just takes one power cycle, sometimes it takes a half-dozen.  I plan on troubleshooting that in the near future (hopefully not out of necessity), which I will definitely write up.  I also plan on writing up my attempts to get my Commodore-64 online in 2020.ev, which is going to be entertaining for me and possibly of nostalgic interest to a couple of folks out there, and possibly a history lesson for other people.

I honestly could not have done this without the insights from many people out there, from the folks who collected all of the different revisions of Commodore hardware and figured out what it took to future proof them (figuring out what should go into all of those recap kits is a nontrivial task) to the other retro enthusiasts out there.  Thanks to Perifractic of Retro Recipes for answering my dumb questions about using a C64 with a modern flatpanel display.  Thanks to the 8-Bit Guy for planting the idea in my head that maybe, just maybe I could do the same stuff he does on his channel and resurrect my closest childhood friend while I'm stuck at home.  Thanks to Jan Beta for his work restoring Commodore equipment on his Youtube channel and figuring out how to build a new C64 power supply (even though mine doesn't work (yet)).  Thanks to the C64 Wiki for being my first stop for all the fiddly stuff, including power connector pinouts.  And a hearts-felt thank you to the retrocomputing community, without whose long years of diligent work researching and archiving all things Commodore I could not have accomplished any of this.