Video: Modding a consumer TV to use RGB input

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Drew Sebastino
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Video: Modding a consumer TV to use RGB input

Post by Drew Sebastino » Sun Oct 21, 2018 7:02 am

I thought this was pretty fascinating:

https://youtu.be/DLz6pgvsZ_I
https://youtu.be/NkpSBK3g-gA (Followup video)

I'm really shocked at how well the picture turned out; it looks just like an arcade monitor. Really, if you wanted to build a custom arcade cabinet, you could save yourself from having to buy an expensive monitor and save an old CRT in the process. All of my CRTs are newer models with component though, so it isn't worth the effort (not that I'm knowledgeable enough anyway, and you really need to be when working with high voltages...).

The one advantage would be for consoles like the SNES that natively output RGB, you wouldn't need an adapter for component. Of course, you would still need to either make a plug adapter for SCART, or just make your own cable.

Something unfortunate I noticed though with how this mod is implemented, is that the onscreen display gets knocked out when using RGB. I wonder if you could make something on some perfboard a stick it in the TV; it would just have to look for if the microcontroller is outputting the blanking signal and use the microcontroller RGB output if so and the RGB input if not. I have no idea how you would actually implement this though.

The one thing I didn't understand were the extra resistors 6 minutes into the video; they were never really explained.

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Re: Video: Modding a consumer TV to use RGB input

Post by lidnariq » Sun Oct 21, 2018 12:06 pm

Drew Sebastino wrote:Something unfortunate I noticed though with how this mod is implemented, is that the onscreen display gets knocked out when using RGB.
What do you mean by "knocked out"? When both the video overlay and external source are driving at the same time, the voltage received by the 'jungle' IC is even higher. Look at https://youtu.be/DLz6pgvsZ_I?t=906 where he's got the service menu overlaid on top of the Tandy 1000's DOS.
The one thing I didn't understand were the extra resistors 6 minutes into the video; they were never really explained.
What extra resistors? The circuit after modification looks like this:

Code: Select all

redOSD --R1--+--- "jungle" IC
             |
             R2
             |
redEXT ------+
             |
             R3
             |
            gnd
R2+R3 has to be equal in resistance to the original pulldown before it was removed; otherwise the OSD will get brighter or dimmer. The exact value of all three together are either chosen for impedance matching, and/or are chosen to reduce the voltage from the external source to the range expected by the "jungle" IC.

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Re: Video: Modding a consumer TV to use RGB input

Post by Drew Sebastino » Sun Oct 21, 2018 1:05 pm

lidnariq wrote:
Drew Sebastino wrote:Something unfortunate I noticed though with how this mod is implemented, is that the onscreen display gets knocked out when using RGB.
What do you mean by "knocked out"? When both the video overlay and external source are driving at the same time, the voltage received by the 'jungle' IC is even higher. Look at https://youtu.be/DLz6pgvsZ_I?t=906 where he's got the service menu overlaid on top of the Tandy 1000's DOS.
You're right; I was confusing this for a similar video I watched later where enabling the RGB input completely disabled the onscreen display. It is a minor shame that it is only still being blended together somewhat rather than overlayed; it's probably not worth the effort though.
What extra resistors? The circuit after modification looks like this:
That's what I was referring to; I guess I didn't think too hard about it...

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Re: Video: Modding a consumer TV to use RGB input

Post by tokumaru » Sun Oct 21, 2018 1:34 pm

At first I thought this was a really cool and simple mod, but it doesn't solve the biggest problem with retro consoles which is the fact that CRT TVs won't be around for long and modern TVs have really poor support for them. If I attempt something like this I might end up ruining a CRT TV and I'll be worse off than I was before!

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Re: Video: Modding a consumer TV to use RGB input

Post by Drag » Mon Oct 22, 2018 7:04 pm

It's probably just meant to be a cool and simple mod, not an end-all be-all solution to declining technology. :P

Also, I believe the actual cathode-ray-tubes are still manufactured, just that nobody's using them in TVs anymore.

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Re: Video: Modding a consumer TV to use RGB input

Post by lidnariq » Mon Oct 22, 2018 7:08 pm

If they're not using them in TVs, what are they using them in?

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Re: Video: Modding a consumer TV to use RGB input

Post by koitsu » Mon Oct 22, 2018 9:26 pm

Space ships.

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Re: Video: Modding a consumer TV to use RGB input

Post by tokumaru » Mon Oct 22, 2018 9:42 pm

And since they aren't widely used anymore, manufacturing costs have likely gone way up, right?

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Re: Video: Modding a consumer TV to use RGB input

Post by rainwarrior » Mon Oct 22, 2018 10:01 pm

Drag wrote:Also, I believe the actual cathode-ray-tubes are still manufactured, just that nobody's using them in TVs anymore.
There actually seems to be a sizeable market for new low-end CRTs in Asia. (Not quite sure why, though.)

From what I understand the quality is pretty low. Not sure if it's something you'd really want to use. Here's a search on Alibaba. You might notice that most of these require you to buy 100 at a time:
https://www.alibaba.com/trade/search?SearchText=crt+tv

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Re: Video: Modding a consumer TV to use RGB input

Post by pubby » Mon Oct 22, 2018 10:39 pm

tokumaru wrote:the biggest problem with retro consoles which is the fact that CRT TVs won't be around for long
But surely CRTs will be around longer than the game systems. I bet there exist 1000 CRTs for every NES.

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Re: Video: Modding a consumer TV to use RGB input

Post by tokumaru » Mon Oct 22, 2018 11:16 pm

pubby wrote:But surely CRTs will be around longer than the game systems. I bet there exist 1000 CRTs for every NES.
Based on quantities, I guess you're right, but I believe TVs have a higher failure rate than old game consoles (how many TVs from the 80's are still in working order?), and for a particular individual it can be a hassle to go hunting for a "new" CRT. The fact that they exist SOMEWHERE doesn't necessarily mean they're easily accessible to any retro gamer.

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Re: Video: Modding a consumer TV to use RGB input

Post by Drew Sebastino » Tue Oct 23, 2018 1:50 am

I'm curious, what is typically first to fail on a CRT TV anyway, if you can narrow it down like that?

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Re: Video: Modding a consumer TV to use RGB input

Post by TmEE » Tue Oct 23, 2018 2:34 am

Cathodes wear out, leading to discoloration, particularly in dark areas. On better things that use cathode calibration this process won't be visible until end of line for the tube (10...40k hours, depending on tube).
In electronics side there's the usual electrolythic capacitors issue and to lesser extent HV transformer going out. There aren't a whole lot of things that go out in them. Modern tubes (high end stuff in eraly 90s and most rest since 2000s) use impregnated cathodes which last much longer than things in 80s and earlier, several tens of thousands of working hours before image gets unacceptable.
On a tube that shows discoloration laready you can probably boost filament voltage and you can a bit more life out the thing. A really beefy video amp that can drive even the most worn cathode into cutoff would also help but such things were never pursued and nowdays it would be quite hard to get that going as high voltage and high bandwidth transistors are no longer made. Computer monitors fail earlier simply because their video amps cannot drive the tube as hard as TV amps can, they usually have 50...80V swing while TV amps got up to 180V, much more playroom. TV amps can afford it though as their bandwidth is much smaller and slew rate limits don't really enter the picture :P

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Re: Video: Modding a consumer TV to use RGB input

Post by Memblers » Tue Oct 23, 2018 4:31 pm

lidnariq wrote: If they're not using them in TVs, what are they using them in?
X-Ray machines? :P For actual display use, I'd imagine there's a niche market for replacement parts for expensive long service-life stuff, like military equipment. There may be some kind of reasons to prefer it in some situations that I can't think of. For example, I work with cryogenic equipment, we build some nice vacuum fluorescent displays. Our older stuff, and competitors' stuff, uses LCD displays. But when you take a rack out of the freezer, and that cold air hits the LCD, it becomes useless. VFDs don't have that problem. They also don't have any issues with viewing angle or contrast. VFDs seem to be heading in the same direction as CRTs.

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Re: Video: Modding a consumer TV to use RGB input

Post by lidnariq » Tue Oct 23, 2018 5:07 pm

I picked up a Planar EL320.256-F6 from a ham swapfest more than a decade ago. Gorgeous display, similarly suitable to extreme conditions. Never figured out anything to do with it, though.

I occasionally longed for their 640x480x9color (3 levels each red and green) display that used the VESA internal Feature Connector. Waaaay to expensive for me to justify.

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