I’m a geek, you’re a geek, we’re all geeks.
And sometimes geeks decide to build computers from the 80s.
Today’s article is showing the step-by-step progress of building the Commodore 64.
Click here for more articles on the Commodore 64
This article is a direct follow up of the article about modern-day construction of Commodore 64.
Jump to sections of the construction:
Components
Construction
Testing the board
Installing the chips
First boot
Deep board testing
Closing the caseA lot of different replica motherboards were discussed in the previous article about building a brand new Commodore 64.
During the planning and acquisition phase of the project, we decided to get the toms01 250466 Commodore 64 motherboard replica from forum64.de (it is in German so google translate helps.)
The main rationale to choose this specific motherboard was that Restore-store.de (no affiliation with wereallgeeks) had it in stock, in a nice flat black solder mask, it was affordable, and the store also had in stock some of the key elements needed for the build.
Thing is, some of the components required to build the computer are not available in the average local surplus store, and sometimes not even in bigger online stores like Digi-key or Mouser…
Here’s some specialized online stores that were useful in acquiring C64 components.
(none of these have any affiliation with wereallgeeks)
- CBM-Retro (in finland)
- The store may be located in finland but it is in english
- Reactivate micro
- The Retro 8-bit shop
- Restore-Store (in Germany)
- Restore-store is in german but the owner answers to english
- Google translate helps
- Retroleum (in the UK)
No single “speciality” store has everything. Acquiring the whole set of components is a side quest on its own and can be time consuming.
That is without even talking about the specialized MOS chips that makes the commodore 64 the computer that it is. We’re talking here VIC-II, SID, PLA, CIA, MOS6510 CPU…
Sourcing these generally mean finding a dead C64 and salvaging the parts.
Sadly, the scarcity of the MOS chips makes it interesting for money-eager sellers to purchase old commodores to destroy them and sell the parts, which is counter-productive for the Commodore hobby as a whole as it reduces the number of working C64 for no valid reason… luckily, there are modern replacements for SID, PLA, ROMS and even CIA!
A word on chips counterfeiting
There are unscrupulous sellers out there and sellers with bad suppliers that do sell chips that will not work on the Commodore 64 as advertised – it is always a great idea to test components when they arrive to ensure they will not cause the build to fail. More on this matter in this article.
It may not always be possible to test each and every chips, but purchasing away from an unreliable source comes with it’s share of issues – receiving a non-working component is possible so compromises have to be made.
Components, components, components
It may take some time to gather the whole set of parts required to completely populate the C64 main board, but here’s what most of the components required to build one Commodore computer looks like
Contruction
Construction begins with the bare motherboard. The matte black finish of this toms01 motherboard is quite nice and somewhat artistic in its own rights.
To assist with assembly, the C64 parts locator from aranet will be quite useful. While designed for a Sixtyclone motherboard, the part placement is the same, being both replicas of the same Assy 250466.
This app shows where components are placed. The idea is to use this as a guide when installing the components. It is somewhat of an interactive Bill-of-Material and will help to avoid soldering components at the wrong place.
Building from the ground up
A way to easy soldering, is to build from the ground-up. This means putting the lowest form factor first, and building height as time goes. While it is interesting to put large connectors quickly to see where things goes, they will quickly be in the way when populating smaller components. The motherboard will be flipped upside-down quite often in the process, and holding small components in place is easier on a flatter surface.
Resistors, inductors, small axial capacitors, diodes
First up, the small axial capacitors, inductors, resistors and diodes. There are quite a lot to install. They are the smallest height of anything to install, and won’t be in the way for the next steps.
It is best to always validate visually that the soldering looks good before passing to the next component, making sure there is no damage done by the iron, etc. It is also a good idea to clean regularly with isopropyl alcool to remove excess flux. Testing with a multimeter isn’t a bad idea either.
One of the axial capacitor – C38 – is in charge of the restore key. One common issue with this key on the commodore 64 is that it needs to be pressed harder than other keys to register, and changing the value of this capacitor to 4.7nF solves this issue. That modification is described on the uwaterloo site of Peter Schepers. The mod is so common that online stores sell the capacitor as a “C38 restore key mod” – it is also easier to find than the original value of 51pF.
The bigger capacitors, and even the “flat” ceramic ones, will wait for further steps to facilitate installation of everything.
Sockets. sockets, sockets
There are several integrated circuits (ICs) to be installed on the commodore. Instead of soldering them directly to the motherboard, it is wise to install sockets. This way, the chips don’t have to be desolder for future changes, tests, mods, fixes, etc.
A nice side effect of sockets is to not solder the chips at all; One has to be less careful when dealing with sockets than with the chips themselves.
It is also possible to alter machined pins to be used as a socket of sorts for the crystal; this may be an interesting option for anyone that may want to test the differences between NTSC and PAL.
Transistors, regulators, fuse
Once the smaller parts and every sockets are installed is a good time to begin with bigger/higher components. The most complex ones are the voltage regulator and TIP29 transistor, as they are meant to be heatsinked. The 7805 5V linear regulator releases a particularly high ammount of heat and requires more sinking; getting a proper heatsink helps. Alternatively, switching retulators can be used to replace the linear ones; in which case no heatsink is even needed.
Transistors and regulators need their legs to be prepped for installation. The fuse socket is more straight forward.
Small ceramic capacitors
There are lots and lots of tiny ceramic discs as they serve to filter power at each IC on the board, in addition to their various use in circuitry.
The problem with small ceramic capacitors is that they are thin discs. Delaying their installation after the chip sockets was a strategic move, as the sockets are actually helping with holding these discs in place while soldering them. Having chip socket bodyguard will also help to prevent damaging them.
There is a Tentalum capacitor at C15 that is noteworthy – Tentalums may look like ceramics, except they are polarized…
Connectors
Installing the connectors is one of the most fun part of building the computer – it is what is visually visible from the outside of the box, the doorway to the machine.
Keyboard, LED, IEC, Audiovideo, game controller ports, cartridge port, power connector… this is what the user actually … use.
But it is also the tallest parts on the motherboard and thus being added near the end, not to be in the way of all other components during their installation.
Axial power capacitors
Similar height than the connectors are the large power capacitors. Commodore always just populated them with axial so that is how toms01 designed this replica motherboard. They are the largest capacitors on this board but being placed sideways don’t bring up too much height.
Bridge rectifier and line filter
The line filter was installed last simply because it is a coil that is somewhat fragile by comparison to other components.
The bridge rectifier placement is at an 90 degres angle. A bridge rectifier is essentially a series of diodes placed to take AC on one side and bring DC to the other. It is essential to match the + and – location of the part to the ones on the motherboard.
This [almost] concludes soldering for the motherboard, but at this point the RF modulator is still missing. When installed it will link the VIC-II chip to the outside world, so it will be required before oeprating the computer.
But before installing anyting on the board, let’s validate construction went well.
Quality check
Testing is the only way to be sure that construction was well done. There is no point in running a dead test or diagnostic cartridge until we know for sure to have correct voltages and there is a valid video output. The next few steps are to make sure of that.
Some of the same process is seen performed by Noël’s retro Lab on this Youtube video.
Bare motherboard testing
Chips in the commodore 64 are rare and pricey. And fragile, which is why they are becoming scarce.
Before putting the chips (or any replacement) in the sockets, best is to validate all and every voltages on the motherboard circuitry. NOW IS THE TIME TO CONNECT THE POWER SUPPLY and turn on the bare but assembled PCB – complete but without ICs. — the fuse needs however to be installed.
There are many voltages of interests on the circuitry alone. Every chips are getting power. Underpowered chips won’t function, but overpowered chips will die.
Here are the results of several test points on the newly assembled motherboard. YMMV.
VSS @ 12V for MOS-6567
Only when all the voltages look safe is it time to populate the chips and sockets. The same voltages can be re-tested when the chips are in. A bad chip can bring some voltages down.
Before installing the chips
An interesting way to begin populating the chips is to go step by step and validate things are working at every phases.
Clock circuit
The Commodore 64 works with a base clock that is different for NTSC and PAL, and all of that derives from a clock circuit using one crystal and MOS8701 chip.
For NTSC the master clock runs at 1.023Mhz and for PAL 0.985Mhz.
This derives from the crystal at Y1 – 14,31818MHz for NTSC and 17,7344MHz for PAL – but also from J2, the NTSC/PAL jumper.
It is important to match the crystal with the jumper settings to get a valid clock speed for the CPU and match all that with the proper VIC-II chip, otherwise the output video won’t match any standard and will likely not display at all on modern equipment.
Strange fact – the replica motherboard comes jumpered but the silkscreen makes it look otherwise. Don’t ask how we know…
Testing VIC-II input clocks
Before anything can be done, a valid display needs to be established. For this to happen, not only does the VIC-II chip require power, but also input clocks – two of them. the dot clock, and the color clock, at pins 21 and 22.
Populating only the MOS 8701 and crystal permits to validate these clocks are correctly set. Without these clocks, the VIC won’t be able to generate a valid screen. Using an osciloscope and poking the pins 21 and 22 proves the circuitry is correctly built.
At this point it would be tempting to add the VIC-II chip and test it, but there’s still an essential part of the video circuit missing.
RF Modulator
This area was meant to populate a circuit to modulate RF, it was used by the computer to connect to the TV via an 75 ohm aerial cable connection. This is no longer possible on modern TV.
On every revisions of Commodore 64 motherboards except the original one, the modulator was also used to process the video signal, mix it properly, and send it to the AV connector. Without this modulator, no visual output will occur on the 250466 motherboard.
There are a few RF board replacements out there and it may be an idea to socket them for the test run in order to ensure proper results before passing to a permanent solution.
This circuitry is required to achieve correct video output, seen on pins 14-45 as Color and Sync/Luminance. Poking these signals would result in a time-based signal without much coloration. If the circuit is OK, that would result in the screen being displayed black, but the osciloscope would show even a non-standard set of circuit.
At this point, the VIC-II and clock circuit is working, hooking this up to a monitor shows a black screen. It would be futile to go any further until it is possible to output an image… but once an image is obtained, it is time to go ahead with the other ICs.
Populating the board
Now that the VIC-II chip is properly setup to generate a valid [but black] image is a good time to populate the whole Commodore. Again the C64 parts locator from aranet is useful to make sure all the small ICs are in the right place.
Once everything is in place and power is applied, the computer will boot up. The same pins 14-15 would be much more active because of all the colorful activity.
It’s ALIVE!
If all went well and every components are functionnal, the commodore 64 will show a usual boot-up screen for the first time.
Booting is one thing, what about making sure everything is OK?
Dead test and diag
The Commodore can be setup to run with only a partial set of chips. The dead-test cartridge runs in ultimax mode – essentially using the capability of the C64’s predecessor, the Commodore MAX. In this mode, the CIAs aren’t required, as well as the ROM chips. the SID chip can also be omitted.
That leaves memory, logic chips, VIC-II chips and CPU as the bare minimum, as long as there’s at least a black screen showing.
Regardless if the board seeminly works or not, best is to put the newly made commodore 64 to the challenges of Dead Test cartridge and fully-harnessed diagnostic cartridge. The idea is to figure out if any circuit and chip is not behaving as expected; and to resolve any issue preventing the machine from running at peek efficiency. There are a number of diagnostic tools available to C64 hobbyist, and the harness can be home-built.
The goal of this test is to get an all-good status on the inner components; not having this might mean bad chips or issues with the soldering job. The harness helps the software dig deep into what’s functionning correctly and what’s not.
Note that having a non-original Kernal or other ROM chip might get detected as faulty. That is why most geeks keep one original ROM image on their ROM switcher such as the Kernal Quattro.
Closing the case
Once the commodore is fully debugged, there’s only one step left to get a complete Commodore, and it is the outer shell. In this case, a used breadbin style case from a dead C64 which signed its organ donor card, and a keyboard from an online auction, that required a good cleaning.
Conclusion
Acquiring all the components for building a Commodore 64 can be tidious and take some time, maybe even more than constructing said computer. But building a computer is rewarding. The machine isn’t just any machine, it is very personnal. One of a kind. Decisions were made on components, soldering was done by hand, this Commodore 64 has something more than any other.
It is a fun project. Not a cheap project, but very rewarding.
And it is not over! more mods and updates to come…
Related articles
Building a C64 in 2023 (wereallgeeks)
toms01 250466 motherboard (forums64.de)
restore-store (restore-store.de)
SID replacement (wereallgeeks)
BackSID test and comparison (wereallgeeks)
PLA replacement (wereallgeeks)
Character ROM replacement (wereallgeeks)
ROM replacement (wereallgeeks)
CIA replacement (wereallgeeks)
J-CIA -CIA replacements (wereallgeeks)
A word on chip counterfeiting (wereallgeeks)
C64 parts locator (aranet.net)
Restore key mod by Peter Schepers (uwaterloo.ca)
C64 diagnostic tools (wereallgeeks)
C64 diagnostic harness (wereallgeeks)
Noël’s retro Lab (YouTube)
Noel’s retro lab testing a sixtyclone build (YouTube)
RF modulator replacement for C64 (wereallgeeks)
Customize C64 ROM chips (wereallgeeks)
Cleaning retro keyboards (wereallgeeks)
We are All Geeks! 
Pingback: Building a Commodore 64 in 2023 – We are All Geeks!
Pingback: We tried the J-CIA on our Commodore 64, here’s how it was – We are All Geeks!