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 Post subject: Re: TV RGB mod thread
PostPosted: Fri Nov 18, 2016 3:06 am 


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8)

Image

Image

Still needs a little tweaking but the PoC works. Unlike the PiP.

cruzlink2 wrote:
Thanks for the reply knuckle here is a link to a better picture http://imgur.com/mxdFLSm .


Well, it said BLK but the 300 V further up tells me you should stay away from that pin. I don't see a blanking pin as usual, but the fact it says "RGB/YUV insert" sounds hopeful. I'd poke around, maybe it switches automatically? Or with an I2C signal? Dunno enough about this to give a proper answer.


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 Post subject: Re: TV RGB mod thread
PostPosted: Mon Nov 21, 2016 6:20 am 


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I don't think I made it clear enough, the setup above has the external RGB mod while keeping the OSD RGB.

I can now see the volume level and adjust the picture with RGB as the reference. It makes it almost look like it came with RGB from the factory. This also has the benefit of getting rid of the big ass 4P2T switch, just a small on/off for the blanking.


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 Post subject: Re: TV RGB mod thread
PostPosted: Mon Nov 21, 2016 1:46 pm 


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KnuckleheadFlow wrote:
I don't think I made it clear enough, the setup above has the external RGB mod while keeping the OSD RGB.

I can now see the volume level and adjust the picture with RGB as the reference. It makes it almost look like it came with RGB from the factory. This also has the benefit of getting rid of the big ass 4P2T switch, just a small on/off for the blanking.


That's awesome! Is this potential doable for every osd-hack RGB?


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 Post subject: Re: TV RGB mod thread
PostPosted: Mon Nov 21, 2016 3:32 pm 


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Yup, it'll work with any TV that works with this mod. It essentially replaces the 4P2T switch with a Linear Technology LT1675. I've got it using the OSD blanking signal to very rapidly switch between the two RGB sources; "pixel switching" as I found out.

The best part is that it can be made for about $10. In addition to the LT1675, it uses two other ICs, an on/off switch, six capacitors and nine resistors.

I had the thing designed more than a month ago and I was trying to figure out how to make PCBs since (along with fucking around with my new SNES and Genesis flashcarts and the OSSC I'm now assembling). After a weekend spent trying to make the toner transfer method work without success, I decided that the plain transparancies/photoresist/UV exposure method can't be that bad. Well, my photoresist STILL hasn't arrived so I got a prototyping board with surface mount pads fine enough to rig up a prototype.

Image

That's it in the middle, flapping in the breeze, supported by wires lol. I'm glad the picture's blurry because frankly it looks like a mess. There're some details to work out, like why the image is a little bit darker/dimmer than usual, but it works! Once I can actually print my PCB, make some minor changes and eliminate the shitty board layout as a problem and move some components around, I'll put the circuit up on github or something.


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 Post subject: Re: TV RGB mod thread
PostPosted: Mon Nov 21, 2016 4:42 pm 



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Yea Knuckle I thought the same thing about the blanking pin not really being a regular blanking pin. In this diagram you can see that the OSD is done internally inside the jungle IC, so therefore no need for external blanking. I am starting to think that the rgb points are just an extra input that might have been used in a more expensive model, I read the user manual and it points to unused ports that are for a optional component input/scart in the European model. So maybe this input does not need any blanking I think because it's an actual input and not an OSD/RGB in for the menu. I will give a shot to just plugging in the pins and seeing what I get. Thanks for your replies again.


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 Post subject: Re: TV RGB mod thread
PostPosted: Mon Nov 21, 2016 11:44 pm 


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KnuckleheadFlow wrote:
Yup, it'll work with any TV that works with this mod. It essentially replaces the 4P2T switch with a Linear Technology LT1675. I've got it using the OSD blanking signal to very rapidly switch between the two RGB sources; "pixel switching" as I found out.

The best part is that it can be made for about $10. In addition to the LT1675, it uses two other ICs, an on/off switch, six capacitors and nine resistors.

I had the thing designed more than a month ago and I was trying to figure out how to make PCBs since (along with fucking around with my new SNES and Genesis flashcarts and the OSSC I'm now assembling). After a weekend spent trying to make the toner transfer method work without success, I decided that the plain transparancies/photoresist/UV exposure method can't be that bad. Well, my photoresist STILL hasn't arrived so I got a prototyping board with surface mount pads fine enough to rig up a prototype.

Image

That's it in the middle, flapping in the breeze, supported by wires lol. I'm glad the picture's blurry because frankly it looks like a mess. There're some details to work out, like why the image is a little bit darker/dimmer than usual, but it works! Once I can actually print my PCB, make some minor changes and eliminate the shitty board layout as a problem and move some components around, I'll put the circuit up on github or something.


That's seriously cool. :)
I love stuff like this. I will try to get your design into a set if I can.
Have you ever seen this blog? This guy is driving guns to make a vector machine. Wonder how repeatable this stuff is on better sets?

https://spritesmods.com/?art=bwidow_fpga&page=1


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 Post subject: Re: TV RGB mod thread
PostPosted: Mon Nov 21, 2016 11:51 pm 


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Oh yeah, I've seen it. One of my pie in the sky, future mods is "big screen Vectrex".


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 Post subject: Re: TV RGB mod thread
PostPosted: Tue Nov 22, 2016 12:22 am 


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cruzlink2 wrote:
In this diagram you can see that the OSD is done internally inside the jungle IC, so therefore no need for external blanking. I am starting to think that the rgb points are just an extra input that might have been used in a more expensive model, I read the user manual and it points to unused ports that are for a optional component input/scart in the European model. So maybe this input does not need any blanking I think because it's an actual input and not an OSD/RGB in for the menu. I will give a shot to just plugging in the pins and seeing what I get.


How will the TV know it's receiving RGB through those pins, and to display it? I understand you're seeing internal blanking elsewhere, and the set is capable of it, but I'm not sure that equates to it working automatically. I have a Samsung PoS that when set to the auxiliary AV channel looks blue until fed sync, whereupon it blanks itself. So if you get the RGB to display, but something else is displaying behind it, or even just the blue, you might try that. I couldn't find a way to turn my RGB inputs on though, as I think it was I2C controlled. I'd be interested to hear how you get on as it might help me get further :)

EDIT: I think my problem might be that without the remote I can't get to the primary AV channel, only to the secondary one, which won't display RGB.


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 Post subject: Re: TV RGB mod thread
PostPosted: Wed Nov 23, 2016 5:53 am 


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In fact, I'd love some advice for modding a Samsung HiTron TV-488. I'm not having any luck finding the service manual, but it uses this Philips IC (TDA8841) - https://my.mixtape.moe/hiflqk.pdf.

(This post was a mess,so I've tried to clean it up from here)

What I'm doing -
Feeding PSOne Luma to the secondary AV line - shows up as B&W
Feeding 5V to pin 26 of the jungle chip - blanks the display
Feeding RGB to pins 23 thru 26 after that - does nothing, no image appears at all.

However, feeding amped RGB onto the output pins of the jungle chip instead (pins 20 thru 22, nominally 2Vp-p) shows a stable picture, but it's not a great picture. It starts very bright with retrace lines, and then fades away to a very low brightness level over a few minutes. Disconnecting and reconnecting things sometimes brings the image back up to retrace brightness.

I'd really prefer to use the chip's RGB inputs, if anyone can help...

EDIT: ok, so looking at the PCB, the Micom feeds the neckboard directly, it doesn't feed the jungle chip. Its outputs meet up with the jungle IC outputs and thence to the neckboard. There are components missing on this revision that would allow it to feed the RGB inputs of the jungle IC, as well as/instead of the outputs - it looks like all you'd have to do is swap over one diode for each colour to fork to the inputs instead. If i did swap those... what would happen? I wonder if there's a way to turn on the RGB inputs? or am I using the wrong blanking pin?


EDIT: Ok, the Service manual is here - https://my.mixtape.moe/zwwyvm.pdf Taken me months to find it, and finally, once i post here, i clued into something. My has the TDA8841 one chip, NOT the 8842 as shown. And the Micom is the non-TTx version, on the very last page. There might be a different manual for the Australian version, with the 8841 shown. Maybe it doesn't have the RGB inputs enabled?

it should work on the secondary AV channel? I can't get to the primary one (rear of the set) without the remote...unless pulsing something into pin 41 of the Micom will do something... anyone know how to do that? +5V logic level?

EDIT: No dice. I don't think this jungle IC takes RGB in, though the schematics from philips say it does. Or if it does, it's being blocked over the I2C bus. That's why the Micom feeds it's own RGB to the neckboard. I should test the levels of that, i suppose.


Last edited by buttersoft on Sun Nov 27, 2016 12:57 am, edited 8 times in total.

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 Post subject: Re: TV RGB mod thread
PostPosted: Wed Nov 23, 2016 9:21 am 



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Cool Knuckle!

I will try this when I get some spare time and see if it works with my JVC.

My original post here: viewtopic.php?p=1211477#p1211477

KnuckleheadFlow wrote:
Wow, do I feel stupid. If your TV's jungle IC needs it, going from 0.7 Vpp to 0.5 Vpp is dead simple. Looking for video attenuation examples I realized that superguns with SCART connectors need to do this to drop the ~3 Vpp JAMMA RGB to 0.7 Vpp.
I had a look at this guy's supergun and long story short, a 30 Ω resistor in series with the RGB input before the 75 Ω terminations will make a voltage divider that'll attenuate the typical console's 0.7 Vpp to 0.5 Vpp.

My reasoning being that in the above supergun we've got:
Code:
JAMMA RGB in (3 Vpp) ---[R1 180Ω]---[optional 250Ω pot]--- --- AD8073 amps then SCART RGB out (0.7Vpp)
                                                          |
                                                          |--- AD725 encoder IC
                                                          |
                                                       [R2 75Ω]
                                                          |
                                                          |
                                                         GND


For our purposes we can ignore the AD8073 amplifiers (probably) since that's accounting for the RGB being split to his encoder IC (AD725) and SCART connector. All that matters is the voltage divider. A regular resistive voltage divider is:
Code:
V in ---[R1]--- --- V out
               |
              [R2]
               |
              GND

with
V out = R2/R1+R2 * V in


So with that supergun, R1 is 180 Ω (+ optional 250 Ω pot) and R2 is 75Ω to go from 2.3 Vpp (I guess that's the typical JAMMA RGB signal and the pots are there for stronger boards sending 3 V?) to 0.7 Vpp. Our R2 will also be 75 Ω and we want to go from 0.7 V in to 0.5 V out so...
Code:
0.5 V = (75Ω / xΩ + 75Ω) * 0.7 V
...
x = 30Ω


Add a pot along with that 30 Ω resistor in case you get something with stronger signals and Bob's your uncle. It's really simple and I'm surprised it took me this long to figure out.


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 Post subject: Re: TV RGB mod thread
PostPosted: Tue Nov 29, 2016 4:44 am 


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Knuckle that is very, very cool. The only reason I didn't reply is sometimes these forums tell me when new posts have been made to this thread and a lot of times it doesn't.


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 Post subject: Re: TV RGB mod thread
PostPosted: Tue Nov 29, 2016 10:37 pm 


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Buttersoft, your experience resembles my first attempt on a 20" trinitron TV - fading from too bright, briefly "just right", then going darker. I did not ever properly solve it, so if you figure it out, I'd be interested in what you did.
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 Post subject: Re: TV RGB mod thread
PostPosted: Wed Nov 30, 2016 3:44 am 



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Trying to RGB mod my 32" Panasonic TV, model CT-32G13W. I removed the OSD lines and tapped in my RGB and pulled blank high to 5v. I hooked up my Neo Geo MVS and used the composite in for sync. Here is what I got right off.
Image

Just need to figure out how to get those bars out of it. This is the only thing I have to test with at the moment. I don't have any other consoles with RGB at the moment, more to come of course! So what is left to do to get this working good?


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 Post subject: Re: TV RGB mod thread
PostPosted: Wed Nov 30, 2016 4:40 am 


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Nice to know I'm in good company. As i said, the schematics for Asia (and presumably for Australia) show a separate Micom chip, and that separate chip feeds the neckboard directly. I don't see why you'd bother, if you didn't have a cheaper Jungle IC that didn't take RGB-in. The Euro version, or some instances of it, had SCART - and I note that cheaper versions of the chassis used exactly the same components, but had a SCARTkill resistor to jump the ability to switch SCART on, in some way. My board seems to have that resistor, but removing it made no change.

I'm guessing the problem i have with delivering amped RGB direct to the neckboard lies in delivering too much current, and there's some sort of feedback loop reacting to that. Or possibly that the RGB im' producing isn't amped right, and the black level is resetting, again via some sort of loop. But those are just guesses - Tim will no doubt come in and tell me I'm wrong again ;) I think if I build a two stage amp, using back-to-back 7314's, i can get a stable picture,but i want to confirm that. And doing so produces a ton of noise. Earlier in this thread I did read about turning down the contrast, colour and brightness to nothing. I'll give that a try, and try to measure the RGB coming out of the Micom directly as well.

mikejmoffitt wrote:
Buttersoft, your experience resembles my first attempt on a 20" trinitron TV - fading from too bright, briefly "just right", then going darker. I did not ever properly solve it, so if you figure it out, I'd be interested in what you did.


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 Post subject: Re: TV RGB mod thread
PostPosted: Wed Nov 30, 2016 2:01 pm 


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Devalis wrote:
Trying to RGB mod my 32" Panasonic TV, model CT-32G13W. I removed the OSD lines and tapped in my RGB and pulled blank high to 5v. I hooked up my Neo Geo MVS and used the composite in for sync. Here is what I got right off.

Just need to figure out how to get those bars out of it. This is the only thing I have to test with at the moment. I don't have any other consoles with RGB at the moment, more to come of course! So what is left to do to get this working good?


Seeing as how some of the bars go behind the characters while some go in front makes me think the problem is with the MVS and not the TV. Do you have an arcade monitor to connect it to?

From what I can tell, the picture looks dope, other than the bars. Any mods to the MVS? I'd have thought the voltages would be too high for a TV, more in the 2-3 Vpp range. Got a spec sheet for that Panasonic's jungle IC? Curious as to what voltage those RGB pins expect.


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 Post subject: Re: TV RGB mod thread
PostPosted: Sat Dec 10, 2016 7:59 pm 


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Well......it is with great sadness that I inform you I've modded my 32" sony CRT TV into one that doesn't work. I just don't have the skills required to work on things that have small surface mounted components. Time to admit defeat and just get another TV that has component YPbPr input and use a SCART converter instead.

Dang....


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 Post subject: Re: TV RGB mod thread
PostPosted: Sun Dec 11, 2016 5:54 am 



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I figured out the lines were caused by a bad connection. I reseated the cart and the picture came in bright and clean. The only thing that worries me a little is when the screen goes white, the lettering at the top and bottom will move off screen. I don't know if it's supposed to do that or what. Also, I need to know if I need to put any input protection on my new RGB input...

also, here is the datasheet on the jungle IC

http://pdf1.alldatasheet.com/datasheet- ... 5165K.html


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 Post subject: Re: TV RGB mod thread
PostPosted: Sun Dec 11, 2016 1:57 pm 


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mikejmoffitt wrote:
I picked up another 25" TV today intending to do a tube swap on a Neo-Geo machine. If the tube swap doesn't work out, it's still a good tube and TV, so I'll see about RGB modding it. At a glance the OSD looks RGB-driven, so I bet it will not be difficult.

Have you ever connected an MVS (or any other arcade board) to an RGB-modded TV chassis? Consoles are one thing, but impedance mismatch is giving me fits. I've been banging my head against such a project for a couple months, but can't get it quite right.


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 Post subject: Re: TV RGB mod thread
PostPosted: Sun Dec 11, 2016 6:20 pm 


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How are you reducing the MVS's RGB signal (< 3 Vpp) to the TV's level (< 1 Vpp)? Earlier I posted a link to a DIY supergun with SCART RGB output. Take a look at that.


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 Post subject: Re: TV RGB mod thread
PostPosted: Sun Dec 11, 2016 7:08 pm 


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berq wrote:
mikejmoffitt wrote:
I picked up another 25" TV today intending to do a tube swap on a Neo-Geo machine. If the tube swap doesn't work out, it's still a good tube and TV, so I'll see about RGB modding it. At a glance the OSD looks RGB-driven, so I bet it will not be difficult.

Have you ever connected an MVS (or any other arcade board) to an RGB-modded TV chassis? Consoles are one thing, but impedance mismatch is giving me fits. I've been banging my head against such a project for a couple months, but can't get it quite right.


I've connected a bunch of MVS systems to my RGB modded TVs and nothing was out of the ordinary. I terminate my outputs with a 75 ohm resistor in series on the output, to match the termination of the TV.
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 Post subject: Re: TV RGB mod thread
PostPosted: Mon Dec 12, 2016 5:17 am 



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The only other thing I've hooked it up to is a Sony PVM, and it looked great on there.


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 Post subject: Re: TV RGB mod thread
PostPosted: Mon Dec 12, 2016 5:25 am 


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Devalis wrote:
when the screen goes white, the lettering at the top and bottom will move off screen. I don't know if it's supposed to do that or what.


If you mean the whole image gets larger when it gets brighter... It's called bloom, and no, it's not really meant to happen. It always does though, even on the best sets a tiny bit, getting slowly worse as time goes on. I think it's the caps aging, though it by no means indicates they're about to fail.


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 Post subject: Re: TV RGB mod thread
PostPosted: Mon Dec 12, 2016 6:11 am 



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I was thinking about recapping the set anyway. So you think putting the 75 ohm resistors on the output on the MVS will bring the voltages into range? If so, should I also put one on the sync?


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 Post subject: Re: TV RGB mod thread
PostPosted: Mon Dec 12, 2016 7:58 pm 


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KnuckleheadFlow wrote:
How are you reducing the MVS's RGB signal (< 3 Vpp) to the TV's level (< 1 Vpp)? Earlier I posted a link to a DIY supergun with SCART RGB output. Take a look at that.

That was a good read. Thanks. Unfortunately, even with the MVS signal divided down to the right voltage, the image is still too dark.
I'd get into more detail, but this thread is getting kinda schizophrenic with all the different projects converging on it. Which is cool. I like that so many people are pumping new life into CRTs. But I'd already started chronicling my progress over on the neo-geo.com boards. If you're ever over that way, I'd be honored if you'd stop by.


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 Post subject: Re: TV RGB mod thread
PostPosted: Mon Dec 12, 2016 11:00 pm 


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If you are losing dark details, and/or you are having streaking issues depending on the game / content, you might be having a clamping problem.
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 Post subject: Re: TV RGB mod thread
PostPosted: Tue Dec 13, 2016 4:41 pm 


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buttersoft wrote:
If you mean the whole image gets larger when it gets brighter... It's called bloom, and no, it's not really meant to happen. It always does though, even on the best sets a tiny bit, getting slowly worse as time goes on. I think it's the caps aging, though it by no means indicates they're about to fail.


I think some monitors are worse than others regarding blooming. I fully recapped an old arcade monitor recently (some 30+ caps) and now the picture is nice and the colors are great, however, it blooms just like it did before.

Turning down the brightness helps somewhat.


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 Post subject: Re: TV RGB mod thread
PostPosted: Tue Dec 13, 2016 5:03 pm 


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Shoryukev wrote:
Well......it is with great sadness that I inform you I've modded my 32" sony CRT TV into one that doesn't work. I just don't have the skills required to work on things that have small surface mounted components. Time to admit defeat and just get another TV that has component YPbPr input and use a SCART converter instead.

Dang....


A little off topic but I hope this doesn't discourage you (or anyone else) from further modding. Don't throw that TV out yet, though. You may get there soon enough. First surface mount mods I did looked like balls. Literally; solder balls all over the place. So bad even Drakkon would've sneered at it. Surface mount stuff can be tricky, but a little practice gets acceptable results. The caveat being you need 5 other things:

1) a temp controlled soldering iron. There are good-enough Hakko knockoffs like the $24 YiHUA 936
2) small (0.8-1.2mm) wedge/screwdriver tips. Forget those bullshit cones.
3) fine and ultra fine solder. Having 0.015" diameter really helps with small stuff
4) magnification. Not to inspect, but to use while you work. I use a stereo microscope, but one of those big magnifying lenses on a flexible arm, or those glasses with the jeweller's loupe things should do. My vision is like the one thing that hasn't started going to shit, I really didn't think I needed magnification but I always wanted a microscope and got a good deal on eBay. I quickly realized having one that everything blownup like that made my movements significantly finer somehow. And I'm rather clumsy working with my hands.
5) *copious* amounts of flux paste. Smear that shit. Plain rosin flux is cheap, works good though it can be a little annoying to clean

With those, it really just takes a handfull of times practicing on junk PCBs to get you there. That said, though I can lay down a hundred picture perfect joints on surface mount ICs, caps and resistors still give me headaches and often end up slightly askew. So it goes.

Dave Jones of the EEVBlog on youtube has some good, detailed videos for this. Some people can't stand his voice but it never bothered me lol.

berq wrote:
That was a good read. Thanks. Unfortunately, even with the MVS signal divided down to the right voltage, the image is still too dark.
I'd get into more detail, but this thread is getting kinda schizophrenic with all the different projects converging on it. Which is cool. I like that so many people are pumping new life into CRTs. But I'd already started chronicling my progress over on the neo-geo.com boards. If you're ever over that way, I'd be honored if you'd stop by.


Hmm, shame about that. I'm thinking about making a CMVS myself, leaning towards using an 1C.


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 Post subject: Re: TV RGB mod thread
PostPosted: Tue Dec 13, 2016 7:02 pm 


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KnuckleheadFlow wrote:
Shoryukev wrote:
Well......it is with great sadness that I inform you I've modded my 32" sony CRT TV into one that doesn't work. I just don't have the skills required to work on things that have small surface mounted components. Time to admit defeat and just get another TV that has component YPbPr input and use a SCART converter instead.

Dang....


A little off topic but I hope this doesn't discourage you (or anyone else) from further modding. Don't throw that TV out yet, though. You may get there soon enough. First surface mount mods I did looked like balls. Literally; solder balls all over the place. So bad even Drakkon would've sneered at it. Surface mount stuff can be tricky, but a little practice gets acceptable results. The caveat being you need 5 other things:

1) a temp controlled soldering iron. There are good-enough Hakko knockoffs like the $24 YiHUA 936
2) small (0.8-1.2mm) wedge/screwdriver tips. Forget those bullshit cones.
3) fine and ultra fine solder. Having 0.015" diameter really helps with small stuff
4) magnification. Not to inspect, but to use while you work. I use a stereo microscope, but one of those big magnifying lenses on a flexible arm, or those glasses with the jeweller's loupe things should do. My vision is like the one thing that hasn't started going to shit, I really didn't think I needed magnification but I always wanted a microscope and got a good deal on eBay. I quickly realized having one that everything blownup like that made my movements significantly finer somehow. And I'm rather clumsy working with my hands.
5) *copious* amounts of flux paste. Smear that shit. Plain rosin flux is cheap, works good though it can be a little annoying to clean

With those, it really just takes a handfull of times practicing on junk PCBs to get you there. That said, though I can lay down a hundred picture perfect joints on surface mount ICs, caps and resistors still give me headaches and often end up slightly askew. So it goes.

Dave Jones of the EEVBlog on youtube has some good, detailed videos for this. Some people can't stand his voice but it never bothered me lol.


It hasn't discouraged me, but I know my boundaries. I am just terrible with dealing with really small parts right now lol, I'm sure at some point I'll get better at it. Kinda sucks I butchered the TV, but I got it off craigslist for free a few years ago anyways so I'm not sweating it. I really need to get a magnifying glass and an articulating table clamp to hold things while I work on them. I've modded several of my consoles and enjoy the projects.

If nothing else at least I already found a replacement, found a 32" JVC CRT with a high line count on craigslist for $20 to use until I get good enough to try again. It was dealing with the surface mount capacitors on the board of my Sony that did me in lol


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 Post subject: Re: TV RGB mod thread
PostPosted: Wed Dec 14, 2016 2:33 pm 



Joined: 07 Aug 2006
Posts: 486
Location: Sydney, Australia
buttersoft wrote:
I'm guessing the problem i have with delivering amped RGB direct to the neckboard lies in delivering too much current, and there's some sort of feedback loop reacting to that. Or possibly that the RGB im' producing isn't amped right, and the black level is resetting, again via some sort of loop. But those are just guesses - Tim will no doubt come in and tell me I'm wrong again ;) I think if I build a two stage amp, using back-to-back 7314's, i can get a stable picture,but i want to confirm that. And doing so produces a ton of noise. Earlier in this thread I did read about turning down the contrast, colour and brightness to nothing. I'll give that a try, and try to measure the RGB coming out of the Micom directly as well.


Don't attempt to drive the neck board with the signal directly from an AV device. It's not going to work.

If you want to replace the RGB preamplifier (ie the jungle IC) with your own it must have the following features:
1) Clamp the AC coupled video to a DC level so black is always at a constant voltage.
2) Provide variable gain and bias adjustments that are different for each channel. They need to be adjusted so they match the characteristics of the picture tube (this is done by the jungle IC normally, with settings stored in the micro's EEPROM).
3) The gain must be electronically variable by the ABL (Auto Beam Limiting) voltage. This basically a measurement of the anode current into the picture tube. If it is too high the contrast should be decreased, which causes the anode current to go down. It's an essential feedback loop. Without it a bright scene may cause the high voltage supply to drop out of regulation and as that's directly connected to the horizontal output stage it causes geometric distortion too.
4) The video needs to be blanked during retrace. The allows the user to turn up the brightness without seeing retrace lines. The blanking signal timing is normally generated from the signals fed back from horizontal and vertical output sections.

buttersoft wrote:
Nice to know I'm in good company. As i said, the schematics for Asia (and presumably for Australia) show a separate Micom chip, and that separate chip feeds the neckboard directly. I don't see why you'd bother, if you didn't have a cheaper Jungle IC that didn't take RGB-in. The Euro version, or some instances of it, had SCART - and I note that cheaper versions of the chassis used exactly the same components, but had a SCARTkill resistor to jump the ability to switch SCART on, in some way. My board seems to have that resistor, but removing it made no change.


The micro's OSD out is muxed with the output of the jungle IC because some versions of the chassis require the RGB input for SCART. If one version has to be this way, might as well make them all like that. The TV design engineers don't want to work too hard. The OSD is digital and is generated by the TV itself. Because it's digital there's no need to bother with clamping and blanking. It restricts the generated video to what it can safely do without beam current feedback.


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 Post subject: Re: TV RGB mod thread
PostPosted: Thu Dec 15, 2016 12:10 am 


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Joined: 24 Jul 2016
Posts: 255
viletim wrote:
The micro's OSD out is muxed with the output of the jungle IC because some versions of the chassis require the RGB input for SCART. If one version has to be this way, might as well make them all like that.


Sometimes you’re so far ahead of me I have trouble following. The last 6-7 pages of the schematic are the connection diagrams. The Euro version’s TTX micro feeds the TDA8842’s RGB inputs (though not the blanking pin?) My version has the Non-TTX micro, which feeds the neckboard. And it has a TDA8841, without SECAM capability, not the 8842 shown. Is that what you were saying...? Aren't there two versions, that work slightly differently?

Schematic - https://my.mixtape.moe/zwwyvm.pdf
Jungle IC - https://my.mixtape.moe/hiflqk.pdf

The datasheet for the TDA8841 indicates RGB inputs, I just can’t get them to work. If they’ve been disabled internally, or by the micro, would replacing the chip, maybe with a higher-end 884X, work? If not, or if I can’t find one, is there a chip you’d suggest?

Thanks for the reply, the help you provide is amazing. If you’re willing to post, I’m willing to listen.

EDIT: I do wonder if there's a mistake in the schematic, in that the EU version's TTX micro does feed the blanking pin. The TTX-Bus connection on the micro shows a wire for it.


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