LG 21FJ6RB CRT TV RGB Hack / Mod - PLEASE HELP

[tiobolinha]

UPDATE: I got image with the component in I added to the TV but the image was missing CR and CB signals I don't know why. It looks like a software issue on the microcontroler options (maybe it was locked somehow as the original design of the TV didn't have component in) but I can't tell for sure.

Unfortunately this was as far as I got. I will look for another CRT, one with better options on the board to add direct RGB (like an external OSD IC sending RGB to the Jungle IC or SCART in on the board).

Thank you everyone for the support.

This project is now closed. 


Hello everyone,

After sucessfully having native resolutions on my first cabinet now I want to make a new junior cabinet for my daughter.

For that I have a 21" LG 21FJ6RB CRT TV which will be perfect.

The downside is that this TV doesn't have component input so I'll have to either hack the chassis to drive signal directly to the RGB circuits or neck or to hack a YCrCb input on the back pannel.
 
I downloaded the original service manual and it seems that this same board is used for other models and it has YCrCb circuitry available although the back pannel only has composite input.

I have no idea on how to do this kind of hack but I'm really interesting in learning. Does anyone has experience with this TV set or any LG flaton?

Attached 01: is the part of the circuitry board where I spotted the YUV input. I checked the actual board and the points are really there. Also I spotted an option for "CrCb In" in the Service Menu which comes disabled from the factory.

Attached 02: Is the neck circuitry which is the only place I spotted RGB. It's really easy to feed RGB signals in there but I'm not sure on how to do it. I have to take R, G, B, H sync, V Sync and GND from the VGA output and stick in there somehow. kkkk.

Please please help.

Thank you!

[tiobolinha]

Hello people,

I did a lot of research and put together my first thought on how to attempt to hack RGB into this TV. It's the OSD method!

They say that the OSD messages are displayed directly in the cannons via RGB so it overcomes any other signal that the screen is showing. When the TV is scanning, a digital pin in the Jungle IC generate the pulses needed to form the OSD messages in the screen.

That said, the idea is to:

1) Stick the RGB signals from the PC's VGA Card in the OSD's RGB lines that comes out from the jungle IC to the CRT cannons.

2) To make the OSD RGB cover the entire screen we have to spot the OSD's digital pulses pin in the jungle IC and feed 5v to it.

3) The sync signal will be took from H sync and V Sync pins from the PC's Vga Card, scrambled together (Amra's / rCadeGaming's composite sync circuit) and feed to the TVs composite video input.

DONE.

I spotted those pins in the TV's jungle IC. Attached is a sketch on what I'm planning to do. I also attached the TV's full schematics.

You guys with electronics knowledge and CRT TV hacking experience, PLEASE PLEASE help me. I know you are out there! kkk.

Really appreciate any help you can give.

Thank you!
Marcelo.

[Paradroid]

Firstly, make sure you read this and this a few times. They're the most helpful links I've found on the topic.

You've got the general idea but when I've done the hack I've inserted RGB into the Jungle IC rather than trying to feed RGB directly to the neckboard. The problem for you is that your Jungle IC doesn't seem to have any RGB inputs (only an output). If you read through those links you'll understand why this is a problem (matching the expected output signal level).

It does look like you have a YUV input there. You could try that... or just find another TV that has a Jungle IC with an RGB input.

In my experience, they're pretty easy to find. In fact, I now have a stockpile under my house (14", 20", 21", 25", 29", etc.) for future projects.

[tiobolinha]

Firstly, make sure you read this and this a few times. They're the most helpful links I've found on the topic.

You've got the general idea but when I've done the hack I've inserted RGB into the Jungle IC rather than trying to feed RGB directly to the neckboard. The problem for you is that your Jungle IC doesn't seem to have any RGB inputs (only an output). If you read through those links you'll understand why this is a problem (matching the expected output signal level).

It does look like you have a YUV input there. You could try that... or just find another TV that has a Jungle IC with an RGB input.

In my experience, they're pretty easy to find. In fact, I now have a stockpile under my house (14", 20", 21", 25", 29", etc.) for future projects.

Thank you so much for the reply. I know you have done this before so I'll follow your advice.

Rob also told me to just get another CRT but I'm in Brazil and in here there's not as many options as there's in the US. Unfortunately. 

Talking about YUV in: It seems like LG use this same board for other models that have a "DVD in". There are a bunch of missing components in the board (capacitors, resistors, etc) in the YUV path. I'll just put it in there. That's the easy part.

My main concern is telling the microcontroler to enable YUV. In the Service Menu there's an option called "CrCb IN" which is disabled by default. Do you think this is it?

I attached the table with the Service Menu options so maybe you can spot something I'm missing.

I really appreciate you guys taking the time to help me out.

Cheers!

[tiobolinha]

I inserted the caps, resistors, inductors that were missing in the YUV pathway as indicated in the service manual.

In the service menu I found some hidden menus where you can enable DVD in and did that.

I got image! It's cristal clear but it seems that only Y is working and Cr and Cb are not. I enabled "CR CB IN" in the service menu and the image keep showing but in green tones.

I didn't find any problems in the lines. In the jungle IC maybe there's another pin that enable CR and CB. Any ideas?

I appreciate any help.

[Paradroid]

Nice work. Sounds like good progress. Sorry, I don't know much about how component signals work so I can't really help any further.

Have you got a Service Manual or Data Sheet for your Jungle IC? With the TDA chips I've worked with, there are detailed manuals that tell you everything about the workings of the IC and what each individual pin does. I'd suggest searching for a document like that if you haven't already done so.

Good luck!

[tiobolinha]

Nice work. Sounds like good progress. Sorry, I don't know much about how component signals work so I can't really help any further.

Have you got a Service Manual or Data Sheet for your Jungle IC? With the TDA chips I've worked with, there are detailed manuals that tell you everything about the workings of the IC and what each individual pin does. I'd suggest searching for a document like that if you haven't already done so.

Good luck!

I found the document. Tonight I'll run some more tests and see if I can manage it to work.

If it doesn't work my only option would be to feed RGB directly to the neck. Have no idea on how I'll sync. I suppose I can't just feed the sync signal to the composite input as the Jungle IC will be bypassed in this layout.

Has anyone in the forum done that before?

Thank you.

[Amra]

I'm not sure if the voltages being sent to the neck are the same as the ones coming from your source signal, or if those 100 ohm resistors would be proper terminating loads depending on the impedance of the source signal.  I believe most VGA termination requires 75 ohm.  100 is pretty close, but might cause some impedance mismatch and thus signal loss/reflection.

Ideally one would need an oscilloscope to compare a properly terminated input RGB signal going into a Jungle IC with the RGB signal coming out of the Jungle IC and going to the neckboard.  This would show if there is any kind of signal processing, attenuation or amplification happening in the process. Meaning, if you are able to get this to work, more than likely you wont have any control over brightness, contrast, hue, color, tint, etc etc, as most of that is handled by the Jungle IC.

However, if you are intent on skipping the jungle IC anyways and injecting the signal after, then it seems there wouldn't be a need to disable the Jungle IC, which should allow you to insert the sync information into the composite signal and let the jungle IC operate per normal to do the sync.  Of course, the caveat of this would be the need to disconnect the RGB output terminals from the jungle IC before injecting the signal into those traces. Perhaps terminate them into a 100ohm resistor sent to ground, then put a 75 or 100ohm resistor in series with the signal source before injecting them onto the traces.

If you decide to go that route, a triple pole double throw switch might let you switch between normal operation and the injected signal.

[tiobolinha]

I'm not sure if the voltages being sent to the neck are the same as the ones coming from your source signal, or if those 100 ohm resistors would be proper terminating loads depending on the impedance of the source signal.  I believe most VGA termination requires 75 ohm.  100 is pretty close, but might cause some impedance mismatch and thus signal loss/reflection.

Ideally one would need an oscilloscope to compare a properly terminated input RGB signal going into a Jungle IC with the RGB signal coming out of the Jungle IC and going to the neckboard.  This would show if there is any kind of signal processing, attenuation or amplification happening in the process. Meaning, if you are able to get this to work, more than likely you wont have any control over brightness, contrast, hue, color, tint, etc etc, as most of that is handled by the Jungle IC.

However, if you are intent on skipping the jungle IC anyways and injecting the signal after, then it seems there wouldn't be a need to disable the Jungle IC, which should allow you to insert the sync information into the composite signal and let the jungle IC operate per normal to do the sync.  Of course, the caveat of this would be the need to disconnect the RGB output terminals from the jungle IC before injecting the signal into those traces. Perhaps terminate them into a 100ohm resistor sent to ground, then put a 75 or 100ohm resistor in series with the signal source before injecting them onto the traces.

If you decide to go that route, a triple pole double throw switch might let you switch between normal operation and the injected signal.

Thank you so much for your comments.

Surely I'll keep this info for the other CRT I'll get to do this project. In the next one I'll make sure to look the schematic ahead of time and make sure it has an easier path to stick the RGB signal in there. I understand that the top oportunities are CRT boards that have either a SCART circuit (Sony Trinitons?) or an external OSD chip sending analog RGB to the Jungle IC.

I won't try to mess up with RGB to the neck as this will get me stuck with all kinds of issues like you said (brightness, color, sharpness controls and so on). At the end our aim is to get perfect image right?

I'm already searching with my sisters, cousins and friends if anyone has a CRT they are willing to get rid of. Maybe I'll get lucky!

Regards