Am I on the right track with this CRT s-video mod? - Page 1
Forum section: electronics / beginners

author: largerat2205
author_rank: Newbie
timestamp: November 01, 2022, 11:19:14 pm
content: Hi, i'm pretty much a beginner with electronics and i'm currently planning out how to s-video mod this crt I got which is a trinitron kv20vm30 I just have a few questions about it. I drew a simple albeit crude diagram that shows where i'm currently at.I've seen a few mods of this sort and some people inject s-video chroma and luma straight into the jungle chip, and others use a switch to switch between either the chroma from composite and chroma from s-video or the lumas. I saw one specific example where someone took the composite signal pin to switch between s-vid and composite luma on a dpdt switch, with chroma being injected only on the s-video side. I don't want to use this method because my rear composite input is a little broken and only works when you push the wire in deep, so I only plan on using my front input for actual composite signals. The switch methods seem to be the most reliable and don't fall victim to weird sync issues so I decided on using a dpdt switch to switch from composite and s-video. Most other examples i've seen using the switch method pull the stock chroma from an unpopulated point and inject it into another point near the chroma input pin on the jungle.Sorry for the long explanation. Judging from my tv's service manual, vcr video is processed on IC402 I think according to the chip datasheet. The actual jungle chip seems to be IC1501 and there is a clear chroma input on that chip from what I outlined in the first attached image. The av inputs from every video type is processed on another chip nearby and its hard to tell what actually is coming out, but it seems it might be switched and split off into chroma and luma right before they are to be inputted into the jungle. I plan to take the stock chroma input from the first point outlined and inject the switched chroma into the second point. There is a capacitor that says 10000P in between the two points and I wasnt able to find a value in the parts list so I assume it might be 0.01uf. I also plan on inputting s-video luma into the composite input pin and use the ground pin for the same input as my s-video ground.However, I have a few questions regarding the logistics of this depending on if the things I picked out from the service manual are correct.1. I plan on doing a 75ohm resistor termination to ground for each s-video ground, should I just solder the resistor in between the two points as seen in the diagram and split the ground wire to go to each ground pin or should I do it some other way.2. Do I need to remove the capacitor in between the two points I outlined or cut the trace or something? Is it fine to just leave it as is?3. I'm gonna add back the cap at switch; is just wiring the cap from the switch pin to the wire fine or should I do it some other way?4. Im not too familiar with capacitors so is there a preference of using ac or dc capacitors with how i'm using it at the switch? Do I need to worry about polarity if I use a DC cap and if so how should I orient it?5. This might be a silly one but I was wondering if I could just leave everything plugged into the board whilst I solder to it. This would obviously be after leaving the tv unplugged for a few days and properly discharging it, but I'm just wondering if there's a risk with working on the board with everything plugged in(or some things plugged in) cause I usually take them out (it would just be a huge pain to disassemble the whole tv and I'm bad with reassembling stuff).Once again sorry for the long post and thank you if you managed to read through it. I'm just gonna note that I don't plan on actually doing this until after thanksgiving when my pinecil comes in, i'm just trying to see if I have the right idea with it so far. I also have not taken a deep look at the inside im just going purely off the service manual.(In the off chance that this post actually gets posted I've been having issues posting this topic all it does it send me back to a blank new topic box when I click post. I have taken off the attachments so hopefully it works and I can link the images in a reply)

author: largerat2205
author_rank: Newbie
timestamp: November 01, 2022, 11:21:23 pm
content: service manual -https://elektrotanya.com/sony_kv-20vm30.pdf/download.html(thank god this thing finally posted sorry for the link I think posting the pdf breaks the post)

author: EPAIII
author_rank: Super Contributor
timestamp: November 02, 2022, 06:12:03 am
content: The two components of the S video signal are just the luminance and chromance signals of composite video. By far the simplest way of using them to drive a composit video monitor (TV) is to simply combine them with a simple resistor network. You can purchase this kind of simple adapter for a very reasonable price. I would search for one that plugs into your existing composit video input.https://www.google.com/search?client=firefox-b-1-d&q=s-video+to+composite+video+adapter+cableAnd if you want to be able to view both/either composit and S video, a switch that is designed for switching composit video would be far superior to a toggle switch. They are also fairly reasonable in price.https://www.google.com/search?client=firefox-b-1-d&q=composit+video+switchAs for your broken input, it is fairly common for these connectors to be mechanically mounted by only the solder joints to the PC board and, when used in a rough manner, these solder traces can break. If you examine the circuit board where this connector is mounted you may find the traces broken. A bit of work with a soldering iron and, perhaps the addition of some bus wire can make a good repair of these types of problems.

author: largerat2205
author_rank: Newbie
timestamp: November 02, 2022, 03:46:15 pm
content: Would using such an adapter not just crush chroma and luma into one and give me the same composite video? My intention is to get the tv to input and display native s-video, and the switch is just kinda an optional thing I decided on so I can plug in a composite input and an s-video input at the same time without potential issues and to clean up some of the wiring a bit.

author: wasedadoc
author_rank: Super Contributor
timestamp: November 03, 2022, 12:39:05 pm
content: Quote from: largerat2205 on November 02, 2022, 03:46:15 pmYes.