After a recent visit to my long-term storage, I picked up a large batch of Philips Videopac consoles to prepare for the store. As with most systems of this era, the only video output is RF, and while many TVs technically still accept it, the image quality is far from ideal.
A bit of Googling reminded me of an old friend: Jani from World of Jani, who demonstrated in this post:
https://blog.worldofjani.com/?p=6438 that he successfully used an Atari 2600 composite video mod board made by TFW8B.com inside a Videopac G7000 with an internal power supply.
Perfect – I have several of those machines here to work on!
At the same time, a friend who I was talking with about the Videopac asked if I could make a through-hole version of the mod board instead of the typical SMD version.
Honestly, it was the perfect reason to finally sit down, take the time and learn KiCad 9 properly. I had only used Eagle in the past – and truth be told, that was many years ago and I argued with that too 🙂
Re-Creating the Board in THT
Since I did not have the SMD schematics, I compared the TFW8Bit board against several classic A2600 composite mods. Eventually I tracked down this page:
http://blog.tynemouthsoftware.co.uk/2018/05/easy-atari-2600-vcs-composite-video-mods.html
The page clearly explaining the important of the 75 Ω resistor, which made it more plausible and not surprising to see that several boards/posts younger than that post also followed the same route.
It also had TFW8B’s initial board – which does not have a capacitor, and the later revision was updated with the extra ceramic capacitor, so I added it to my schematics too – decoupling can’t be a bad thing, and the beauty of THT layouts – even beginners can snip out it’s legs if they insist on a board without it.
And that settled my decision, rather than make a THT board for my friend, and a SMD one for myself, the entire board is still very small in THT, so full through-hole it is.
(RFix schematics)
This turned out to be excellent practice with KiCad – and yes, plenty of swearing was involved – I will happily admit it is not exactly intuitive in it’s usage – but it felt good to finally adopt a modern open-source CAD tool.
Also food for thought – After years of dealing with repairs and who knows how many blurry photocopied schematics, it’s amazing how far we’ve come: professional-grade PCB tools that anyone can use for free!
Once I’ve fully tested everything, I’ll upload the Gerber zip on my site for anyone who wants to build one.
Bill of Materials (BOM)
The RFix board uses only a handful of components:
- 2.2 kΩ resistor
- 3.3 kΩ resistor
- 75 Ω resistor
(important for TV impedance matching!) - 100 nF ceramic capacitor
- 2N3904 NPN transistor
A quick note:
There are a lot of easy/simple videomods – but If you’re building one of these into a console, do not skip the 75 Ω resistor. It’s what properly matches the composite output to the TV’s input.
The 100 nF ceramic capacitor acts as a decoupling capacitor to stabilize the video signal.”
(Insert top + bottom PCB photos here)
(RFix top view)
(RFix bottom view)
Compatible Systems
This little board should work for RF → RCA composite video conversion on many machines, including:
- Atari 2600
- Atari 7800
- Philips Videopac G7000
- Magnavox Odyssey² (likely compatible, but not yet tested)
- Philips P2000T computer
- Sinclair ZX81
- TI-99/4A
Note that the Atari 2600 exists in many different revisions, and each may require slightly different removal or rerouting of parts. Always compare your board against a guide for your exact revision.
Better safe than sorry.
More Soon
The gerbers are sent of to production, and prototype PCBs should be here in 2-3 weeks, so I will post updates when the arrives and have time to test the results on a few consoles.
Once that’s done and there’s no more revisions needed, I will share the gerbers with you all.
Stay tuned.
Tim / BeepFixer