Straight-off-the-bat, this is not a review of the HD-64. Rather, this is a fairly lengthy description of some modifications I made to the HD-64 installation to better suit my needs, and why.
I remember, not all that long ago in fact, stating categorically, that as far as getting decent quality video output from the Commodore 64 was concerned, LumaCode was the only worthwhile solution. I said I wasn't even going to qualify that statement. I said it was a hill I'd die on. Well, turns out I was wrong. That hill it seems was a volcano, and I just got hit by a pyroclastic flow.
So what was the seismic event that just wiped me out? Well, while I was grandstanding, unbeknownst to me, Vittorio Pasucci (aka SideProjectsLab) was working on something entirely new: an RF Modulator Replacement which captures video and crucially audio information from the Commodore 64 VIC-II and SID chips respectively, upscales to 1080p and feeds it out of the C64 via a micro HDMI socket. Importantly, there are no external power or decoder boxes required; just the new board, sitting in place of the original RF Modulator, and a single HDMI cable straight from the C64 to your monitor. Compare this to LumaCode which requires the video cable from the C64, the audio cable from the C64, the RGBtoHDMI external box, its power cable, an HDMI cable from the RGBtoHDMI to the monitor, and if you then want sound, a pair of speakers and all their associated paraphernalia.
An introductory video is here, and the 1st batch was made available in early February 2025 at around $110 (excluding shipping), so not for the faint-hearted.
There are two main parts to the HD-64: the board itself, and an "interleaver". The latter is a modded 40 pin socket with a flexible PCB attached to it. This takes the necessary signals from the VIC-II and transfers them to the HD-64 via that flexible PCB. The interleaver doesn't form part of my modifications, so I won't be mentioning it again.
Before we get to my modifications, it should be stated that the HD-64 out-of-the-box is not plug and play. Some configuration is necessary. Whether this should concern you or not really depends on your skill with a soldering iron. Full details are in the User’s Guide Vittorio has written but in summary there are several jumpers that must be bridged, depending on the C64 you're installing this into, and your preferred set-up. For example:
- SV: O-S. This jumper determines the amplitude of chroma in the S-Video signal. What you do with this jumper is very much dependent on your setup. The C64 itself precedes the S-video standard and is too "hot" to be considered true S-Video. Some modern C64 AV cables compensate for this by including a resistor to bring it to spec. So, if you ever want to use S-Video with the HD-64 and you have one of these cables, and you want to continue using said cable, you want to bridge this jumper in the "O" (original) position. If you want the HD-64 to make the necessary adjustment instead, you should bridge this jumper in the "S" (standard) position. I do have an AV cable with an included resistor so on the vanishingly rare occasions I will want to use S-Video I need to set this to the "O" position, as shown:
- 12v VIC. If you have a 6567 or 6569 VIC-II chip, these use 12V and this jumper needs to be closed. If you have any of the 85xx VIC-II chips, leave it open. I will need to close this jumper:
- AUDIO (R) EXT-INT. If you are just using the C64's standard internal audio this jumper needs to be bridged in the INT (internal) position. However, if you have an audio mod that generates stereo for example, and you want to feed this into the HD-64 instead, bridge this in the EXT (external) position. I have no such mods so I will bridge this in the INT position, as shown below. This will feed the onboard audio to the right speaker. In order to receive "mono stereo", i.e. the same audio from both speakers, the "mono" setting in the configuration software must be toggled "on" and the setting saved. I had to do this a few times before I finally got mono stereo but it did eventually work.
Once configured, it's time to mount and power the HD-64. This is where I decided to do my own thing.
See, putting aside all the really clever stuff, because this design doesn't favor one Commodore 64 board assembly over the other, its attempt to be compatible with everything, and to stay within a reasonable budget, have led to some compromises, especially when it comes to installing in a longboard:
- There is no 5V regulator.
- The risers do not align with the original RF Modulator holes on the C64.
Now, Vittorio has himself said (in relation to something completely different but it's still meaningful): "but hey, every solution has its place and its audience, so I would encourage anyone to find their own way around these kinds of issues, the more the better as far as I'm concerned" so with that, and the fact I seemingly want to create the single most expensive Commodore 64 in the world, ever, I'll bash on, with credit card in hand. That's right kids, this is gonna be really, really expensive.
So, let's look at the lack of voltage regulator first.
Important note: in the event it's not already crystal clear, what follows is only pertinent to a C64 longboard. My modifications are with my 250466 SixtyClone specifically in mind. They may or may not work with other longboards: 250407 or 250425 for example, but they are categorically not meant for the 250469 shortboard.
In the original Commodore 64, the RF Modulator is connected to a 9v unregulated supply. In turn, it has some components to reduce this to 5v. Commodore presumably did this to ensure the RF Modulator was powered separately from the existing 5v elsewhere on the board, isolating it, I guess, to avoid interference. Like the original modulator, The HD-64 needs power and conventional wisdom would suggest this be obtained from the original pins to which the HD-64 must be attached. Pin 1 carries 9v Unregulated and (on my board) Pin 8 carries ground. Vittorio has told me (via Discord) that the maximum current draw of the HD-64 is 230mA (approx.) so we need something relatively beefy - the 5v linear regulator I use in the JaF Sandwich, for example, would become a small conflagration. However, with a suitable switching regulator this is perfectly possible but the HD-64 ignores this for the longboard. Instead we are expected to pick up 5v and GND from the pins of the expansion (cartridge) port connector with wires and clips presumably.
Instinctively, I wanted to use that 9v. It makes sense to me to keep the HD-64 isolated from the existing 5v as with the original modulator, because that's how Commodore wanted it but I am 100% amateur and don't have much in the way of electronics knowledge. The HD-64 is a very different beast from the original modulator and Vittorio clearly deems it unnecessary. Naturally, I reached out to Vittorio and enquired about incorporating a voltage regulator on the HD-64. His reply:
"Yes, it would have definitely been possible, in fact my very first prototype was made that way. One thing to note however is that the 9v-UNREG is actually closer to 10.5v (it's 9vAC rectified) so jumping almost 6V with a linear regulator that would have to carry the entire power of the board would have been tough (it would melt). So then I went with a switching converter, but again that would have meant extra components, so cost is a concern, as well as routing, the area around the RF modulator headers is quite crammed and there are several power planes running under. Another important aspect is that not all longboard RF modulators provide ground on the header, mine doesn't for instance, so I decided to sort-of formalize the fact that the longboard installation needs external power, so at least that's simple, cheap and the same for all."
Vittorio's remark about the lack of ground on the longboard modulator header confused me - see my thoughts on this all the way at the bottom of this article - but I don't suppose it matters one way or the other whether I think this decision was correct; that is the decision and it's his to make, but the proposed solution is not very elegant and I don't want to use the expansion port in this manner. I also have concerns about the extra amperage the HD-64 will draw. If you have a C64 filled with original chips and a power-hungry cartridge plugged in (say a pi1541 with Epyx Fastload or an Ultimate II+L) and a weaker PSU, an additional 230mA on the 5v line is not inconsiderable and as amp draw increases, voltage typically drops. However, I have absolutely no data to validate this concern; it's just a gut feeling that may in-fact, be shit.
I could drone on an on about this, but the truth is I don't know if it's better to power the HD-64 independently as I'm proposing. Perhaps picking up 5v and GND elsewhere on the board is the way to go. I don't know better and I'm not pretending for one second I do. I just want to have some fun and have a play. It's a risk I'm willing to take. In the event you want to copy this, you do so at your own risk too.
The next issue is the risers. The HD-64 is supplied with 4 off-the-shelf nylon 10mm risers which cannot be affixed to anything on the motherboard. Sure, they raise the board by the required amount (to get the HDMI connector to the existing hole in the case), but they are just literally sitting there, allowing the HD-64 to flap about. The suggested solution in the guide is to adhere them to the motherboard with superglue or double-sided tape. Not happening.
Once again, this is what Vittorio had to say when I questioned why the risers (feet) were not aligned with the holes for the original RF Modulator to allow them to be screwed in place:
"The decision was made to put the feet as out of the way as possible to ease routing, and the natural position are the board corners. The primary issue is that they would conflict with some components, like the FPGA itself for instance, which really "has to be where it is" on the board (with some wiggle room, but not much). There is also the fact that the shortboard does not have those round holes in the motherboard at all."
Whilst these are all fair points and these decisions certainly do keep costs down, they were, never-the-less, nearly deal-breakers for me. Had the HD-64 not been, in all other respects, seemingly perfect for my requirements I would have dismissed it right there. But after a few days of deep thought, I figured the benefits of the HD-64 warranted a bit of personal intervention and I came up with a solution that I think I can live with, for my 250466 SixtyClone longboards at any rate. I just don't care about the shortboard.
INITIAL DESIGN
First the power. Obviously I can't change the HD-64: it is what it is. But, a standalone PCB incorporating, for example, a tiny D36V6F5 5v regulator is trivial to make and this particular example is capable of delivering 600mA current - well exceeding the required max spec (230mA) so I ordered a few from the manufacturer in Nevada to play about with. That wasn't cheap incidentally.
Because the HD-64 sits 10mm above the C64 motherboard, there is some room under the HD-64 for a "power-board" to be retained and it would simply need two headers for 9v unregulated and GND in, and two more for 5v and GND out. I'd need to connect these by 4 wires to the HD-64 and that would have to be a bit of a hack as there are no pads or headers specifically for capturing the 9v unregulated and GND like this, but I can try to make it neat. However, whether this is more elegant than the original solution is a matter of conjecture. My initial thoughts re wiring are as follows but I did change this in my actual build - the principle however, is identical.
For absolute clarity then and with reference to the HD-64 diagram above and my proposed power-board shown below:
- Pick up +9v Unregulated from point (1) on HD-64 and connect to PWR IN on power-board.
- Pick up GND from point (2) on HD-64 and connect to PWR IN on power-board.
- Pick up +5v from PWR OUT on power-board and connect to point (3) on the HD-64.
- Pick up GND from PWR OUT on power-board and connect to point (4) on the HD-64.
Note: the manufacturers of the D36V6F5 voltage regulator (Pololu) recommend: If you are connecting more than 28v or your power leads or supply has high inductance, we recommend soldering a suitably rated 33 μF or larger electrolytic capacitor close to the regulator between VIN and GND. This limits the damaging effects of LC Spikes. However, as I'm not putting anywhere near 28v (it will be nearer 11v max) into this, and because when I tested the 9v unregulated with my oscilloscope there were no dramatic spikes, at all, (e,g. during power-on) I have deliberately omitted this capacitor.
Now I just need a way to mount this to the C64 and the HD-64 which segues nicely to...
...Replacing the supplied legs (risers): it is somewhat less than trivial (for me), but it is perfectly possible to design a 3d printable part that aligns with two of the existing holes in the C64 motherboard (which originally allowed the modulator can to be soldered to the board), and which supports and retains the HD-64 at the required height (10mm). This same mount can also be used to securely retain the power-board detailed above. I drew something in Blender and it would look something like this, seen first without the HD-64 but with the power-board (and D36V6F5):
 |
| 3D Render of replacement stand and power-board |
Notice the power-board sits in a dedicated notch, which suspends it 1.65mm above the C64 motherboard. This small gap allows for the through-hole components to come through and be soldered on the underside but the legs will need to be cut VERY short. This just leaves 6.75mm between the top of the power-board and bottom of the HD-64 for the power-board components.
Then the HD-64 is placed on top. Nice to see, incidentally, that sanity has prevailed and the board is only available in black. This is the way.
 |
| 3D render of replacement stand and HD-64 |
The four mounting holes in the HD-64 align with the 4 holes in the stand. I'll put four M3 heat-set inserts into the holes in the stand and secure the HD-64 to the stand with four black M3 screws (6mm long).
Finally a render of the bottom of the stand with the mounting screw positions visible:
 |
| 3D render of stand (underside) |
I will place two M2 heat-set inserts into these holes and use two M2 screws (5mm long) to bolt the whole stand onto the C64 board. Between these screws, and the 8 pin headers connecting the HD-64 to the C64, this should provide rock solid support for the HD-64. Seriously, its going nowhere and the superglue can remain in the tube where it belongs.
So much for the theory. How did it fair in practise?
PARTS AND FIRST BUILD
I eventually took delivery of everything, including the HD-64, on the 14th February 2025.
Preparation of the stand was trivial. I found heat-set inserts went in nicely with my soldering iron set to 250°C. Much hotter than this and I get a lot of plastic oozing up round the edges. Cooler and the inserts take a while to push down. This was the first time I've used brass inserts like this but it won't be the last. These results are more than satisfactory. The completed stand is extremely robust and will survive from now until the Earth melts.
Test fits on both my 250466 longboard and the HD-64 proved successful, so I spent a not inconsiderable time congratulating myself for my ability to convert mm obtained from KiCad measurements, to a real life 3d object, apparently perfectly.
To mount the D36V6F5, I first removed 3 pins from a male header with a pair of plyers, and soldered these bare pins into the VIN, GND and VOUT holes (using a breadboard to hold the loose pins vertically and with the correct pitch) of the D36V6F5. I then soldered the voltage regulator to the power-board with these pins and trimmed any excess with snips. Easy-peasy lemon squeezy. Then I soldered a 4 pin right angled male header to the power-board.
After soldering the power-board together, I tested the (now regulated) 5v line with the oscilloscope and this was a steady 5.07v precisely, giving absolutely no cause for concern. It seems perfect. Viva Las Vegas!
Now the power-board can be placed in the retaining notch in the stand, and the stand in turn screwed to the C64. At this stage the power-board will be loose in the notch but that will be remedied in a moment.
In a change from how I initially planned it (above), I then wired it up as follows:
The wire I used to connect both the 9v Unregulated and 5v is Adafruit 26 AWG Hook-Up Wire Gray. The wire connecting both GNDs is Adafruit 26 AWG Hook-Up Wire Black. This has silicone insulation and is extremely flexible which makes the necessary bending underneath the HD-64 problem free. I cut these to the desired length and crimped female DuPont connectors at one end for connecting to the power-board. The bare wire on the other end is soldered to the appropriate places, as shown above. At each stage I ensured continuity with my multimeter. The force of these wires will hold the power-board firmly in its notch.
Finally, the HD-64 can be screwed to the stand for the final time, being careful not to pinch any of the wires.
IMPORTANT! Before doing anything else, it is imperative to now power-on the C64 to check the 5v and 3.3v LEDs on the HD-64 light up.
 |
| 3.3v and 5v LEDs should illuminate if HD-64 is correctly powered |
These must work before you are safe to connect the interleaver. Assuming they do, power off the C64, connect the interleaver, and that's job done. If they don't, recheck all your connections and solder joints.
 |
| The HD-64 mounted on stand and Interleaver connected |
If the interleaver is connected correctly and the HD-64 is receiving the correct signal, the HDMI LED will be lit when you next switch on.
 |
| HDMI LED illuminates when the correct signal is received |
RECEPTION AND CRITICISM
After all this, I revealed what I'd done on the HD-64 Discord channel. It's fair to say that reception was mixed and can be summed up as follows:
1. The stand was very well received.
2. The power-board, not so much.
Within minutes of posting this on Discord, Martijn from the Retro8bitshop got in touch to see about "mass producing" a simplified version of the stand to sell as an add-on, with the HD-64. Though I had no hand in Martijn's redesign (other than offering some advice) that was still an unexpected and pleasant conversation and I'm perfectly happy for him to do his own thing if others can benefit and indeed, a few weeks on, these are now available here. A few days after that, Dennis Krijnen from Retro-updates enquired about offering the same to his customers. Again, I was happy to oblige and again, if that transpires I'll insert a link here. However, if you wish to print your own copy of my originals, the STL files are below (see RevA for a stand to use with a power-board, or RevB for a stand to use without a power-board).
As for the power-board itself: whilst no-one outright said it was a bad idea, the consensus seemed to be it was pointless: just using 5v from elsewhere on the board is easier and cheaper. No one else seems concerned about keeping the HD-64 isolated as the old RF Modulator was, or increased amp draw on the 5v line.
My own conclusions? I'm vehemently sticking with what I've done. I really like my power-board and see no reason I shouldn't use it on all of my 250466 builds. As I write, it's been working on my test board (as seen in images above) without issue for many hours, but hours isn't months or years so I take the risk that it may fail given the test of extended time. My best recommendation is if you don't want to take any risks, do as Vittorio suggests and just power it with 5v, ignore the power-board and just enjoy the Rev_B stand (see below). Just make sure your existing PSU does correctly provide 5v to the HD-64: in these early (HD-64 batch 1) days, there have already been instances (according to the Discord channel) of incorrect voltages at the HDMI "Hot Plug Detect" (HPD): anything less than 4.9v here could prevent your TV/Monitor from recognising the HD-64 has been plugged in. As we know, I'm no expert, but if you held a gun to my head I'd say this is because of the increased amp demands of the HD-64 on an already heavily loaded 5v line. If that's the case, this is a potential issue my power-board negates. With batch 2 of the HD-64 expected to be available at the end of March 2025, a much larger user base may (or may not) surface more instances of this type of 5v issue. I'll be watching with interest.
PARTS AND COSTS
I've only bought one HD-64 for initial testing so costs below reflect that, but if it works out I will want two more (one for my test board, one for my main workhorse and one for a new build I'm undertaking on commission from a family member this year). So I have parts enough for three complete stands and power-boards plus some spares. Costs shown include shipping and tax.
- I had the stand SLS printed by 3DPrintUK in PA2200 on 11th January 2025. Cost: £59.95 for six prints. Expensive but the results are tremendous.
- Ruthex M3 and M2 heat-set inserts and inserting kit were ordered from 3DJake on 9th January. Cost: £39.80
- The power-board was ordered from JLCPCB on 10th January. Cost: £7.19 for 10 boards.
- The D36V6F5 was ordered direct from Pololu. Cost was £36.83 for 3 boards. Just buying 3 boards was a grievous error - shoulda bought at least 6.
- Total spend: £143.77. I can build 3 complete stands so that's a unit cost of £47.92
- The HD-64 was pre-ordered from Retro8bitShop (first batch) on 6th January. Cost: £108.58
- Grand Total: £252.35.
- Necessary M3 (6mm long), M2 (5mm long) screws, the right-angled header, female Dupont connectors, and Adafruit 26 AWG Hook-Up Wire I just had lying around but these are easy to obtain from Digikey/Ebay/Amazon/Ali-express etc.
FILES
The files provided produced excellent, accurate results using the printing, manufacturing and parts outlined above (note: I specified Selective Laser Sintering for the stand which has no issues with the fine details and overhangs). I provide no guarantees that they will work for you, nor am I in a position to provide any support, and so you use these entirely at your own risk. These files are provided free of charge for personal use.
REVISION A.
REVISION B.
If you do not want to use the power-board but are still interested in 3D printing a stand, the version below, Rev_B, removes the power-board slot and replaces this with two bars which provide both support and enough plastic to allow safe insertion of the 2 × M2 heat-set-inserts on the base of the unit while still providing plenty of clearance for components on the HD-64 above.
GROUND ON THE RF MODULATOR HEADER
It's been stated, more than once as it happens, that a GND signal is not always available on the C64 Longboard RF Modulator header pins (pin 8 specifically). Indeed, in the guidebook for the HD-64 there is the following quote:
"The Shortboard provides the necessary supply voltages (5v and GND) directly on the RF-Modulator header on the motherboard. The Longboard does not provide either..."
Looking at schematics, I just don't see that. For assembly numbers 250407, 250425 and 250466 the relevant parts of the schematic diagrams are as follows (select the picture for a larger image):
 |
| Schematics obtained from zimmers.net |
In all 3 examples (see highlighted area), pin 8 is connected to GND via the carrier select solder jumper. This was used for RF output only and is irrelevant when RF is no longer being used, therefore as far as these 3 boards are concerned, which will cover 90% of longboard C64 owners, ensuring jumper J1 on the C64 is shorted, will always connect pin 8 of the RF Modulator header to ground. What this doesn't show of course, is impedance on that connection, so that may well be a sensible reason not to use this (and is the very reason I changed my wiring from my initial design), but not that GND isn't provided. Do note however, I have no way of testing impedance so I have no data one way or another. I simply changed my wiring out of an abundance of caution.
