Sony Trinitron S-Video/Composite Mod (RF-Only TV) SOLVED

[KPackratt2k]

The cold VCC wire is in the wrong spot, it should be connected to pin 2 of IC401, this is the cold power supply for the optocoupler for the Composite video circuit.

For the Chroma connection from the chassis to the 4-pin connector on the hot side of the mod board: R326 should be lifted from the side connected to the Chroma pin (46) of IC301, then connect YCJ_IN to the jungle chip pin and TV_C to the R326 resistor lifted upward out of the original circuit, it is recommended to use heat shrink tubing to cover the resistor after soldering the wire to it to avoid the risk of shorting out near adjacent components.

[Dolobill]

Thanks a lot for your comments! And also for creating this isolation board!

[Dolobill]

I did the S-video mod on my TV. While it has clearly improved the issues with composite such as dot crawl, I now have signal interference that mostly presents in darker blues. I can't quite capture it in a photo so it's hard to demonstrate.

It's a bit strange because if I toggle the SPDT switch to composite, there is no interference. Both signals use the same final shielded cable to the jungle chip. There is more unshielded cable on the composite side compared to the S-video/chroma. I am only missing shielded cable between the SPDT switch and the isolator board, but that is the same for both signals.

I am hoping it is the console S-video cable that is the issue (N64/SNES). I don't have another cable to test with. I tried using the composite and the S-video cables on an old LCD, and I can't see the interference there, but I'm also not sure how visible it would be on an LCD anyway.

Edit: I’ve done some more experimenting. I bypassed the isolator board entirely and now I do not get the same interference. It has completely cleared up, except that there are now humbars. So the isolator board is doing its job with respect to the humbars, but the interference I am getting seems to have something to do with the board.

[KPackratt2k]

Interesting. For experimenting, can you remove resistor R2 from the mod board and wire a 33 ohm resistor + a 1K ohm potentiometer in series on a solderless breadboard in its place? On one set I modified (the KV-2780R), I originally used a 100 ohm resistor there, but had some noticeable interference, but found that using a 470 ohm resistor in its place cleared it up to the point where it's not noticeable. Maybe if you used a different resistor value, it would go away or at the very least, reduce it.

Another thing you could try to do is remove resistor R5 and install a jumper in its place.

[vol.2]

I am hoping it is the console S-video cable that is the issue (N64/SNES). I don't have another cable to test with. I tried using the composite and the S-video cables on an old LCD, and I can't see the interference there, but I'm also not sure how visible it would be on an LCD anyway.

Edit: I’ve done some more experimenting. I bypassed the isolator board entirely and now I do not get the same interference. It has completely cleared up, except that there are now humbars. So the isolator board is doing its job with respect to the humbars, but the interference I am getting seems to have something to do with the board.

I'm not so sure. The isolator board is using a photo diode to pass the video, so it might just be that it's interpreting the noise in the signal differently. I would at the very least get a high quality cable and see if that makes any difference.

Another thing to check is you cable routing. The PCB was designed in a way that sensitive signals are routed far from traces with high amounts of electrical potential and reactivity, as to minimize noise. Often times, they purposefully route things between ground to further that. If you just tape down bodge wires without decent insulation on the surface of the PCB, that can cause noise in the video.

[Dolobill]

I haven't gotten around to trying any of these suggestions yet. It's certainly possible I might have introduced noise with my cable routing, though I did try moving them around and I couldn't affect the results.

I ended up doing the extremely basic S-Video mod described here: https://crtdatabase.com/crts/sony/sony-kv-13tr24. So far, no issues with humbars or anything. The noise is no longer present. I've only tested with my N64 and SNES so far. I intend on using this CRT with a MiSTer, but I am waiting on a couple cables. I should be able to test it on the weekend. I know it's not ideal, but if I don't see any humbars with the MiSTer, I might just leave it at that.

Edit:
Here's a video of the noise I was getting, in case you're interested. It's more visible in person. https://photos.app.goo.gl/GuWs5QFoQ9L8GgCM8

[KPackratt2k]

Since the publication of my optocoupler PCB for hot chassis TVs with Composite video inputs, I've installed it onto a Sony KV-2092R. The instructions for installing it are the same as the KV-2780R, so I'm including a link to its page for anyone who has this model (or a similar one) looking to modify it for S-Video input.

viewtopic.php?p=1567430#p1567430

Here's a photo of a close-up of Super Mario Bros (on an NESRGB modded console) for an example of its quality:


You can see more photos of it in this Imgur album: https://imgur.com/a/GhJrRdR

I've also revised the optocoupler board as I've noticed a few changes that I felt were necessary to make (replacing the 2-pin Chroma I/O connector with a 3-pin to provide grounding for shielded wire, adding a 4pF capacitor in parallel with resistor R7, and adding a second mounting hole for future mounting bracket designs). You can order the revised PCB on OSHPark:
https://oshpark.com/shared_projects/XefR2KEe

The revised schematic (click the spoiler to view):

Spoiler

The switching S-Video mod for the TS20 models is in the works, though due to the considerably high cost of ordering sets of 3 PCBs from OSHPark ($83 for three pairs of the required PCBs) along with the complexity of having to pull the shield out of a panel mount jack to make it work as a switch, I may have to either make a cost-efficient version that combines all of the functions into a single PCB or look into selling mod kits somewhere online (maybe on Etsy or Tindie). When/if I offer kits for the switching mod (approximately $60 per kit), I'll include a 3D-printed mounting bracket and a switching panel mount S-Video jack to help balance out the cost.