Guys! Help me RGB mod a television!

[benzaldehyde]

Hey all, long time no write!

I've been out there among the wilds modding amongst the beasts and such, and so my mods have begun to skew a bit esoteric.

And by that, I'm bullshitting and mean I'd finally RGB modded everything and started in on controllers.

However, I am returning to RGB with a bit more knowledge and slightly larger balls. We have a TV (RF only), and I want to patch the RGBS signals into the circuitry after the decoder. I know this is troublesome, as televisions can be quite varied! I am primarily looking for some general pointers; perhaps a repair databse or something.

Alas, Google is aiding me little in my quest. Any chance you fine gents can help a bum out?

[ido8bit]

We'll need a lot more information to get anywhere, though if this TV is so old that it only has an RF input this could be difficult (some really old sets used color difference drive, that is there is no straight RGB in the set at all, even at the CRT board).  Any particular reason why you are sticking with such an old set?

Does it have on-screen display or teletext?  Both can be places to patch an RGB signal in.  

[viletim!]

Trying to do this on such an old TV might be a bit tricky unless you know your way around a TV. As ido8bit mentioned, newer TVs with a/v inputs, teletext and an OSD often have an RGB input of some variety to the jubgle IC (main signal IC). With an old set you're going to have bypass the jungle IC and put your video straight into the RGB output stage.

When you do this you've got to do a few things to the signal first.
Terminate it with a 75 ohm resistor, couple it through a capacitor and clamp it (cause most game console output AC coupled video) and amplify it. How much you have to amplify it depends a lot on the TV. Better measure it with a CRO first.

Take a look at my AC Coupled Video Amplifier circuit. It's basicaly an RGB input circuit for for arcade monitors (which are nothing more than TVs with the signal processing stuff removed). I think this circuit could be adapted to any TV output stage if the gain is reduced and the controll of the offset adjustment is increased.

Your sync signal or composite video signal (more likely if were talking video games) should be injected between the IF stage and the jungle IC.

I'm not sure why you'd need a repair database unless your TV is broken. Oh an while I think about it make sure this TV doesn't have a 'live chassis' power supply.  

[mr. newbie]

hmm is there a place that can do that or is it strictly a homebrew deal?

[viletim!]

mr. newbie,
You mean a place you can take your TV to be modified with an RGB input? Probably not.

[mr. newbie]

didn't think so thanks.

[benzaldehyde]

Hello again! I have been trying to service an old Sony Trinitron that has a nasty habit of going into a semi-standby after a few minutes of being on.

Well, aside from that, I was poking around for loose/blown components and ran across what look to be R, G, and B signal outputs to the yoke. :D

Thinking that the jungle ic might be nearby, I ran across one certain CXA2131AS ic. Checking a service manual for another, similar model of television, I have discovered that this is in fact the video processor (or so I'm led to believe, given that it seems related to every picture adjustment and such!).

Thusly, I hope to patch some signals into this. However, I have a problem! A datasheet seems all but nonextant! Google is kind enough to return a glut of Chinese vendors, none of whom have a datasheet for download. Neither do any ic databases revealed during my search.

I will continue scouring, but if anyone either has or knows where I can acquire such a resource, I would be most grateful!

[viletim!]

Semi-standby? Old TVs often have problems with solder joints (esp. Sony) and electrolytic capacitors.

The only time you'll find a datasheet for a jungle IC is when the manufacturer of the IC makes it available to other TV mfrs. Sony usualy just make ICs for Sony sets, so you won't find a datasheet online (and an english one probably doesn't exist anyway). But it's no big deal because Sony TVs never seem have RGB inputs to their jungle ICs (unless it's german, in which case it will have a SCART anyway).

[ido8bit]

I was working on a Sony TV/VCR combo last night that did have RGB inputs at the jungle IC.  In this unit they were only used for the OSD, but there was on unpopulated space on the PCB for an "RGB processor" IC and a SCART connector suggesting that a similar model does have an RGB input.  

Then fault in this set was that it was completely blanking the video while displaying the OSD.  It caused by a damaged flex cable between the between  the jungle IC and the microcontroller (located on the VCR PCB in these).  I didn't bother looking into it further, but obviously there is a blanking pin on the jungle IC.  This could be used to add an RGB input to such a set via the OSD without needing the missing RGB processor, though obviously there would be no OSD while using the RGB input (I expect the RGB processor is just overlaying OSD over RGB and switching).  

Assuming your set has OSD you could probably do something similar.  If you have the service manual you should be able to find the relevant pins.  
Scope them to see what kind of signal it expects.

[benzaldehyde]

bah! i in fact wish i had a scope! alas, i am no engineer!

a tricky bit here, to be certain. the tv is about 6 years old, and for some reason, after ~5 minutes of use, goes to a dark, green picture of which one may make out some of the onscreen image. i didn't come across any vagrant troubles in the system, but i'll look over the caps again.

the thing does have an osd, though. i found a debug menu manual for the tv, which credited the aforementioned ic with all of the osd fucntions! so i feel i am on the right track. i shall likely try to trace the r, g, and b lines from where they are labeled (leaving the video processing board for the crt) to where they exit the ic.

of course, having an onscreen display is of no real interest for me. thusly, i may just tap the signals into that point and try my luck!

[viletim!]

the tv is about 6 years old

A 6 year old TV with no A/V inputs??? I suppose this is a good example TV differences in different parts of the world. Around here (Australia) A/V inputs have been a standard feature for at least 15 years. So I was assuming you were working on an ~20 year old set.

An analog RGB connection between the mcu and the jungle isn't hard to identify. Look for 4 pins next to each other that connect between the two. One for Ys (rgb switch) and 3 for video. Each video line will come from the mcu, go through a series resistor, then a resistor in parallel to ground (resistor divider) followed by a capacitor (coupling for clamp) to the jungle. If the resistors an caps arn't present then the video is probably digital.

[Endymion]

the tv is about 6 years old

A 6 year old TV with no A/V inputs??? I suppose this is a good example TV differences in different parts of the world. Around here (Australia) A/V inputs have been a standard feature for at least 15 years. So I was assuming you were working on an ~20 year old set.

Ausland is not the only place that is standard, most sets I have seen from the past 25 years USA-side have composite A/V.

My guess is that he is taking the supercheap route here to avoid the pain of defeat on this attempt.

[ido8bit]

Surely it has to be more than 6 years old if it doesn't have any video inputs.  I can't think of any TV made that recently that doesn't have them.  Even those $20 5 inch B&W sets have a composite video input.  

I'd fix the existing fault before thinking about modifying anything.  A dry joint  is the first thing that I'd be looking for, especially if the set will come back on when banged.  If you've already ruled dry joints out it's hard to say where to look next without seeing it.  

[benzaldehyde]

dar! i am putting this on hold for now. i have a 3do image set downloading and i need to get very drunk later and play them.

thanks for all the help, though, guys! i think i need to just break down and learn to use a scope!