Intellivision SECAM Composite Modding Endeavours

A few years ago, I bought a cheap but defective Intellivision console with the intention of fixing it. I also planned to mod it to output composite video, a modification I try to do for all my RF-only consoles. The console came from France and, as is common with systems from there, it was a model that was factory-modded to output a SECAM-format RF signal. Despite my best efforts, I was unable to get this unit working again. After exploring all potential fixes, I concluded that one of the ICs in the system must be faulty. Since this wasn't a high-priority system for me to own or collect for, I decided to leave it as it was and keep the non-functional console for the time being.

That is, until recently, when I bought another cheap system that was functional but in very poor cosmetic condition, with both controllers cut off and missing. This was also a SECAM system. I figured I could combine the two consoles to make one good-looking, functional system. This worked out great, but I still needed to perform the composite mod on the console, and this is where things got interesting.

The different SECAM Intellivisions

While looking at photos of other SECAM Intellivision consoles online, I consistently encountered the same design: a typical Intellivision motherboard akin to those found in NTSC and PAL systems, accompanied by a daughterboard facilitating SECAM output. Much like numerous other Intellivision models/revisions, these systems had a separate power supply board. This all matched up with what the first system I got looked like.

To my surprise, however, upon opening the second system, it looked quite different. It had a more modern-looking PCB, relatively speaking, without the daughterboard. The power supply was integrated rather than being a distinct PCB, with only the transformer being separated from the board. This led me to suspect that this was a much later revision of the Intellivision. Looking at additional online photos seemed to confirm this, as some later NTSC models had a similar design.

The board is labelled 5156-4369 REV PR. I could only find a few photos of similar boards online and very little in terms of concrete information about it. This forum post was the best resource of information and photos I could find.

Finding an approach and installing the mod

While searching for Intellivision composite mods, I repeatedly came across this design by Tim Lindner and Joe Zbiciak. I also found several pre-made boards on eBay and similar sites, most of which seemed to be based on this design. However, many of the listings for these boards mentioned that they are not compatible with SECAM models. This makes sense, given that the common SECAM Intellivision boards lack the standard RF modulator found on other versions.

Since my board did have the RF modulator box, I decided to try the mod anyway. Somewhat surprisingly, it ended up working just fine.

Installing the mod is fairly straightforward. The board I purchased had solder points on one side for video, audio, 5V, and ground inputs, with the other side featuring points for composite video and audio output, as well as a ground point.

I noticed that the legs for audio and video are in different positions on the RF modulator compared to the schematic on the wiki page for the mod. Please refer to the images below for clarification.

To power the mod, I tapped into the 5V from the audio chip after verifying the voltage with a multimeter. I connected the ground wire to a spot near the RF modulator. While these connections can probably be made in several places on the board, these spots worked well for me.

Using a Dremel, I drilled two holes next to the power port on the back, mounted two RCA jacks, and connected them to the mod board.

Note that the photos above were taken while testing things out. After confirming that everything worked, I went back to deep clean the console housing and tidy up the wiring.

The results

I first tested the mod with my Sony Trinitron KV-21LT1B, as that’s the TV I’ll be using with this console the most. According to the manual, it has native SECAM support. The TV handled the signal perfectly, and the picture looked great.

Next, I tested the console with a cheap video converter from AliExpress that’s supposed to convert NTSC, PAL, or SECAM video signals to either NTSC or PAL. While it did detect the signal, it only displayed it in monochrome, regardless of whether I set the output to NTSC or PAL.

Finally, I tested the mod with a generic SCART-to-HDMI converter, which also claims to support SECAM. These converters are widely available online under various names, but they’re essentially the same device. While these have their issues and are generally not recommended for gaming, they can be useful in certain situations. The converter mostly worked, but I noticed some strange ghosting issues with the colors. Below is directly captured footage from the HDMI output.

The issues with the converters are possibly due to their inability to properly handle the 240p SECAM signal from the Intellivision. Alternatively, the signal may be slightly out of spec, which wouldn’t be surprising given the nature of this mod. Unfortunately, I didn’t have any other SECAM-compatible devices to test with, nor do I have an oscilloscope to analyze the signal, so this remains inconclusive for now.

That said, I’m pleased with the outcome, as I can now easily connect the Intellivision to my main CRT TV with a good-looking image. Hopefully, this post will generate some further insights into using this particular Intellivision model and revision with these common mod boards.