TV/Monitor Upgrade Mods

[fj4]

I was just looking to "upgrade" some of my old tubes, a Commodore 1702 (composite/s-video) that may benefit from RGB input, and an 15 year old RCA TV that has an amazingly clear picture but only coaxial input.
I have decent soldering skills and knowledge (4 years of electronics in high school) and was wondering if anyone has managed to find a place closer to the tube in the circuits of their displays to add inputs.
The RCA should be possible, just find which leads on the TV tuner output composite (or luma/chroma), right?  I assume most if not all cable TV tuners output composite.
Just wanted a little advice before I bother opening these suckers up.  
Thanks in advance.

[viletim!]

What you're trying to accomplish is possible but not really feasible for a few reasons:

1. TVs of this age often use a power supply which holds it's ground potiential (voltage) at a fixed point above (or below) earth (real, rod-stuck-in-ground earth). This means that if you were to connect the chassis ground to an earthed piece of equipment (computer, etc) you'll damage the power supply. This voltage can be quite high, often half the rectified mains voltage (340/2 here in australia) and presents a serious shock risk (that's why there's no exposed metal on these old TVs). Just imagine if you connect a VCR to a TV like this... all the exposed metal on the VCR would be at 170v relative to earth, could kill you if you're not careful.

TVs with a power supply like this are know as 'hot chassis' TVs and are identified by the sticker on the back that reads "chassis live contact is dangerious" (again, that's in australia - may be different where you are).

The problem can be solved by isolating the TV - usualy with an isolation transformer. This provides total electrical isolation for the TV. Another way around the problem is isolating the video signal - common practice on TVs when AV inputs where just starting to appear and TVs still had hot chassis. This is done by feeding the video signal through a linear optocoupler.

2. This problem relates to an RGB input. Adding a video input is fairly simple if the TVs has an isolated power supply (most TVs made in the last 10 years, but then again most TVs of this era have a video input anyway), you just need to amplify and maybe clamp (a simple diode clamp should do the trick) the signal and feed it into the signal path between the IF stage and video seperation circuit.

So, knowing this you might think adding an RGB input is as simple as amplifing the three video signals and feeding them to the CRT video drivers (usualy transistors). But it's not that simple! Colour picture tubes are linear when you drive each gun individualy (like a monochrome tube) but when you drive two or three at a time with a linear RGB signal you'll get lots distortion (an overly bright picture). I can't remember the technical reasons behind this (I've got the techincal papers but I don't feel like searching through them at the moment).

The way a TVs video driver output stage (of this era - 15 years ago) works is that it has a chip (known as the jungle IC) that accepts the luminance/crominance and decodes it to either RGB or R-Y,G-Y,B-Y,Y (kind of like "component video" but with proper voltage relationships) which is used to feed the driver transistors.....HA, I could go on forever...Basicaly you need a voltage controlled amplifier which is controlled who's gain is inversly proportional to the beam total beam current (beam current being the ammount of current drawn from the all three cathodes).

Anyway, my point is that it's more trouble than it's worth.

3. TVs are bloody cheap! And because of this people often tend to throw away TVs with easy to fix faults rather than repair them. I think it'd be a lot easier to fix a junked TV (that you colould probably get for nothing) with the required inputs than modify something old.

I'll also make a note here about TVs in Australia. We share a very simmilar TV system with Europe and quite often get TVs with a chassis designed to suit europe, aus, nz, etc. with minimal componet change. What I'm getting at is that a good deal of TVs in Australia made within the last 5 years can be easily modified to accomidate an RGB SCART input. Some chassis just have a junge IC that supports the signals (most common) (sharp, panasonic, centrex, etc) while others have a spot on the board for a SCART socket and spots for the required components - some resistors for termination and some caps for coupling. (found on orion, lg, akai, samsung) And I've also seen a few models (maybe akai?) which had all the required components in place, all that was required was a the SCART socket itself.

Oh, and btw tuners don't usualy output video (with the exception of the new I2C tuners), they output IF.

Fuck that's a long post (i'm not even going to spell check or proof read it). I'd better end it here before I blow a fuse or something.

[fj4]

I figured as much.  The problem is that here in the US, we don't have a standard multi-AV connector like SCART, hence we have 3 options to get RGB: arcade monitor, a tiny RGB monitor, or an upscan converter for VGA, all too expensive.  We have no hot chassis warnings on our TVs other than a generic "Shock Hazard" label.  Thanks for putting me in my place before I hurt myself experimenting.  

[Computolio]

   Just get a Commodore 1084, it's pretty much the same thing you have but with RGB.

   I think there used to be some mod directions floating around on how to convert certain CGA digital-only RGB monitors to do normal RGB, but that kind of stuff is always pretty dangerous.

[Endymion]

The problem is that here in the US, we don't have a standard multi-AV connector like SCART, hence we have 3 options to get RGB: arcade monitor, a tiny RGB monitor, or an upscan converter for VGA

These are not bad choices. At least, they are not as bad as you claim.

1. You don't really need a standardised connector. All this means is that depending on what you get you might need to rewire a plug. Do this the right way (i.e. with a SCART multibox) and you will be doing it once and never have to touch it again.
2. Arcade monitors are abundant and goodly sized.
3. Tiny RGB monitors? How tiny? 20 inch and up are abundant on ebay. That alone makes the monitor you're suggesting on look tiny. If you are patient you will find the one that you want, at the size that you want, and possibly even in a location you can drive to acquire it.

all too expensive.

How expensive is too expensive? I got a Mitsubishi XC series for about 130 last year on ebay. For a 29 inch screen with 15 and 31KHz RGB & VGA I think that's pretty inexpensive.

You didn't even say anything about plasma TVs, many of which tend to work with 15KHz RGB as well as VGA these days. At least, my 50" Panasonic does. There's expensive for ya. (And damn worth it too!)

[fj4]

Apparently I didn't spend nearly enough time browsing eBay.  Searching for "RGB monitor" usually doesn't turn up all the nice-sized ones, just those 13" medical surplus ones and the like  $130?  Damn, that is a good deal.  The Mitsubishi I recently tried to get would have been $248 just for shipping, and that was only a few hundred miles away.

[black18]

If they upgrade mods the good factor was being stable for the standard multi-AV connector like SCART.


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Scotsman Ice Machine

[antron]

I have turned two broken 25" TVs into arcade monitors with this:
http://www.8liners.com/datatech/monitor.html

it's under $100 and works great for 25", but I've heard the 19" don't work so well.  Victor is a very helpful person too.