JaF Sandwich - The Continuing Saga

Ok, it's been several months since the last update and a lot has changed. First, let's recap.

In the first part of this series in which I redesign my JaF64 RF Modulator replacement to become the all new JaF Sandwich I explain why the hell I would want to add an archaic RCA Jack to my design and this can be summarised in one word: LumaCode. In the second part I dedicate some time to dealing with retrofitting the design into my reproduction C64C case and begin to think about adding the ability to deal with experimental LumaCode from the Kawari Mini (Randy Rossi's impressive VIC-II replacement). In the third part I play around with Kawari Mini LumaCode and establish my prototype board works just fine, but that there are issues with the Kawari Mini's LumaCode. In part four I deal with adding the daughter-board to the JaF Sandwich, and explain my continually infuriating problems trying to get the LumaCode from the Kawari Mini to work. This brings us up-to-date: I had a design that functioned exactly as planned, I just needed to finalise the vertical positioning of the RCA Jack and new boards had been ordered.

But. I had a rethink (crowd slaps forehead in unison).

I was messing about with the VIC-II-dizer and the Kawari Mini again  (yes, I know I said I was putting it on hiatus but it nagged the hell out of me) and it very quickly became apparent that constantly dismantling the JaF Sandwich to change the jumpers was an irritatingly poor design choice. In my defence, when I first designed it, I didn't think I would be chopping and changing the video source all that much, but at the moment I am, and dismantling the JaF Sandwich was a pain. So. I redesigned the boards yet again, this time to accommodate a DIP Switch and remove those pesky jumpers. Et voilà:

This is so much better. Now I just need to remember which switch does what. If only there was some way to record this to jog my addled memory...

Unbelievably, I also had to redesign the top board, again. And once again, it was a feature of my reproduction C64C case that prompted this so I suspect an original C64C case will be similarly affected. Along the back of the top case there are plastic wedges which grip the top edge of the bottom half to create a firm join when the two halves are together. I realised one of those wedges was pressing on the top-board when the case was closed and this was actually misaligning the RCA jack. I'm very lucky this didn't break the wedge to be honest. To prevent this, I had no choice but to cut the length of the top board by a few mm to give the wedge clearance. And once again, a whole ball-ache I could have avoided if I'd paid closer attention to the case design.

In addition, I changed production of these last boards from PCBWay to JLCPCB, who, it turns out, can produce a near identical soldermask to the black SixtyClone and is thus an all round nicer match as well as being somewhat less expensive for my particular requirements. I'm not sponsored by either company so am not beholden to anyone. Anyway, all that aside I'm very pleased to report the JaF Sandwich is now complete. Here's a quick snap of that final revision sitting proudly in place:

Over the past few months I've also been writing an extensive description of my progress in getting the experimental Kawari Mini LumaCode to work. After a great deal of effort, it very nearly operates perfectly but there are still a few issues I cannot solve and heavy caveats. This is not an issue with the JaF Sandwich which is doing exactly what it needs to do so I want to keep that process separate. When that is ready for public consumption, the link to that will be here.

Importantly, and the whole reason I added the daughter-board in the first place was to position the RCA Jack nearer to the centre of the corresponding case hole. The daughterboard perfectly takes care of vertical positioning, however if when soldering the RCA Jack I've failed to perfectly align it, then horizontal positioning can be less than stellar. With that in mind, let's see how it looks:

That's about as close to central as I'm ever going to get. Remember, if perfectly central there would only be a 1.87mm gap all round the jack. What you are seeing here is a misalignment of about a third of a millimetre. I can live with that. The RCA cable fits nicely and doesn't hit the hole edges; that was the crucial part. That daughter-board is such a ball-ache I'm really stoked it worked out.

Now, most importantly of all. Does it work?

Course it does! Here's a capture of the Wonderland XII Demo by Censor Design via S-Video (from an original 6569R5 VIC-II chip) and upscaled via a cheap HDMI upscaler. This is using the chroma and luma/sync circuitry on the JaF Sandwich. Audio has been deliberately removed:

Because I generally use a Kawari Mini VIC-II replacement, here's the same demo using the S-Video generated by that:

And here's a capture of the same demo using the VIC-II-dizer through the RGBtoHDMI (no audio). This is using the simple passthrough on the JaF Sandwich:

And here's a capture of the same demo again using the Kawari Mini outputting LumaCode and passing through the JaF Sandwich via the incorporated voltage divider. Once again, there is no audio in this sample:

As you can see, via all four methods utilised to get a video signal, picture quality is just about as good as it's going to get and so that clinches it: as of now, the JaF Sandwich becomes my RF Modulator replacement of choice and takes permanent residence on both my 250466 SixtyClone boards.

It's an unfortunate reality that the Kawari Mini cannot be used with the VIC-II-dizer. However, I am hopeful that in future, perhaps in 2025, Jani Laatikainen's J-VIC will be available as all accounts indicate this FPGA replacement will be a more accurate replica of the original 6569. In which case, pairing that with the VIC-II-dizer will be a winning LumaCode producing combo and one which the JaF Sandwich will cope with admirably.

In the highly unlikely event you fancy building one of these for yourself, read on. If not, no hard feelings (I'm not seriously expecting anyone to bother) and thank you for getting this far through my rambling. It is with some considerable pride and amusement that I can report that in the 18 months it's been available, not a single person has bought the JaF64 PCB. I don't expect anyone wants the JaF Sandwich either :-)

I am frequently wrong however and if building the JaF Sandwich feels like a good wheeze, then I've written a full build guide, which includes the Bill Of Materials and all the necessary Gerber files which are available free of charge for non-commercial use.

Now, I don't want to put you off, but please bear in mind:

• It's really, really expensive. By the time you've bought the minimum quantity of boards, components and paid for shipping you could easily have bought a cheaper, ready made and perfectly good RF Modulator replacement elsewhere, albeit one without the same functionality. The total unit cost of this final revision for me was 26.35 UKP (so 33.30 USD or 31.11 EUR) in April 2024, excluding shipping. The total cost (factoring in everything) is significantly more than that. Figure around 150 UKP (189.56 USD or 177.12 EUR) to fully populate the minimum quantity of boards, shipped. I note the unit cost does compare favourably with The Retro Channel's Longboard Commodore 64 RF Replacement V2 which would sting me £56.58 shipped, however, that is pre-built and it would take a brave man to say that the JaF Sandwich is as good as that as I have not, as yet, been able to obtain one to do side-by-side comparisons (it's been out of stock for a while). That is, never-the-less, something I'm interested in pursuing for purely personal interest as component wise, they are very different beasts.
• You obviously have to source and solder all the components yourself. Though the BOM will help with the former.
• Whilst it works perfectly for my needs, it may not meet yours, for example:
• It might not work on your C64 or clone board
• It might not fit in your C64 case
• I won't be providing any technical support. With a full time job, family and other interests my life is full and happy and I wont make myself miserable fixing other people's problems. Besides, the JaF Sandwich works perfectly for me; if you can't get it to work, that's on you.
• I absolutely will not ever build and sell pre-built versions. I do not have the space or riches to store stock, or the time to build on demand. You're totally on your own.
• Dear PickledLight, can you just add [insert suggestion here]? No. Hell no.

If none of that phases you and you are successful in building one, and if you can be remotely bothered, please drop me an email and show off your efforts with a picture or two.