Seeking help adding composite video to an RF only CRT

[Brad251]

I have done some research on adding composite video to my GE 26GT441/Chassis CTC149C CRT (made in November 1989). I think I have some idea of how to go about adding composite to this set but I wanted to get input from others here. I have a block diagram from a chassis CTC157 that shows how my set is laid out because their main boards are nearly identical. I have the service manual for my set and I also have some pics of the schematic sister that was on the inside back of the chassis that provides a lot of useful info. I do have links to the block diagram, schematic and service manual I am referring to.

​Here is the link to the block diagram and schematic pics:

https://imgur.com/a/KCHKOLs

Here is the link to the service manual which I got from Sam's Photofact:

http://www.mediafire.com/folder/s01b51z ... ice_Manual

​
Based on some Youtube videos I watched where the owners added composite video to their CRTs, I saw that they got the composite video signal by tapping into the video out pin on the jungle chip. My set is different. It doesn't appear to have a video out pin on the jungle chip but rather it has a separate video switching IC (U1401) and audio switching IC (U1402). I'm guessing that I would be tapping into the video out pin (pin 11) on the video switching IC (U1401) for my composite video and then connecting that wire to the composite video jack and terminate that end with a 75 ohm resistor.

​What I am unsure about is whether I should be getting the audio signal from the audio switch IC (U1402), the volume control IC (U1800) or the audio amp (u1900). Page 22 of the service manual shows the schematics for U1401, U1402 and U1900. The separate block diagram I uploaded on imgur shows the pin layouts as well but is not 100 % accurate compared to my set but almost.

​The last thing I'm not sure on is if I have tap directly into each pin or if I have to tap into something directly in line like a resistor or capacitor by removing that component and using remaining pad closest to the IC? In the videos I have watched, the modders, cut the trace leading out from the video output pin. I don't understand why they would do that when they could just remove the first component in line and use the remaining pad.

[Guspaz]

Why composite? It looks like S-Video and/or RGB would be possible.

[Brad251]

On an older set like the one I have, I prefer a softer picture. This is primarily because of nostalgia because I owned similar TVs growing up and the best connection they would have had was composite. Once I step up to s-video and above, the picture starts to look too sharp and it doesn't feel as nostalgic. With that said, my set has great colors but is a very budget set because there are a lot of features and components missing from the main board that were on similar, higher end versions of my set. For example, they released a version of my set that someone just posted about on reddit that was made in 1990 and has composite. For this reason, I will probably just do an s-video mod. I don't think the set I have even has a comb filter.

I did get lucky with this set, though, because it was in a guest bedroom and never used. It feels surreal to have a set this old and for the tube to be in like new condition. Playing NES on this set feels much more authentic than any CRT I have owned yet. I do prefer newer sits for 16 bit systems and up.

[Brad251]

That is cool. I'm not sure how much the blunder tongue would improve the picture quality over the RF modulator I already use which is a Go Video DVD/VCR combo. The picture quality isn't too bad going through the Go Video unit. I suppose I could always get one of these units and try it out. I am currently working on doing an s-video mod to my set as we speak as that is turning out to be easier than attempting a composite mod.

[Brad251]

The s-video mod isn't working out. I have luma and chroma from s-video going to the luma and chroma pins on the jungle chip (via removing the first in inline component and removing the leg closest to the jungle. All I am getting is white horizontal lines with black space in between. I'm guessing this is a sync issue but I'm not sure what to do. I did wind up buying the Blonder Tongue RF modulator you sent me a link to. It is one of the best deals for the price for that model on Ebay. It will be an interesting experiment. Maybe I will be as impressed as that guy in the video. At the very least, I do have a 27" Toshiba CRT from '96 that I will be RGB modding so this 1989 GE set can just be for older content like NES, 80s shows, VHS, etc.

[Brad251]

My Blonder Tongue AM40-550 RF modulator came in and I have been using it with my 1989 GE set for a few weeks. I wouldn't say the picture is quite composite level quality but it look pretty good for an RF connection. I would say it is 85% the quality of composite. Prior to using the Blonder Tongue modulator, I was seeing a lot of noise in the picture and the modulator has gotten rid of 90% of the visual noise. The picture does look a bit sharper as well vs not using the modulator. I would definitely recommend the Blonder Tongue RF modulator if someone has a set that is RF only. I also experimented between using an RG59 and RG6 Coax cable with the modulator and the picture is significantly cleaner with the RG6 cable.

I am very happy with my GE CRT (model # - 26GT441). I am mostly into CRTs for nostalgia and watching 80s/early 90s content and playing NES on this set is the closest I have come to recreating how I remember this content looking on a CRT. I am fortunate that the set wasn't used much.