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Discussion Starter · #1 ·
So I'd like to hook up my dreamcast to my new 30hs420, but there is no vga input to do so.


I've been looking at the schematic for the HS series, looking for places where the RGBHV signal could be swapped in, bypassing another input.


For example, if you look at the signal flow block diagram for the HS, you will see that the HDMI sends either YCbCr or RGBHV to the cxa2171 chip. I was thinking that would be a good place to solder in the RGBHV from a VGA plug, but now I think that the chip probably looking for digital RGB and wouldn't work.


But throughout the rest of the schematic, I'm seeing many places that are labled Rin, Gin, Bin and so on.


So my question is, if I find the right place in the signal path on one of the PCB's, is it possible to add a vga/rgbhv signal that will be properly displayed by the TV?


Or hell, there might even be a spot on the board where they have an RGBHV input but didn't actually wire it to the back of the TV for some reason. Anybody know anything that could lead me in the right direction?
 

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Quote:
Originally Posted by CRTFTW /forum/post/19568199


So I'd like to hook up my dreamcast to my new 30hs420, but there is no vga input to do so.


I've been looking at the schematic for the HS series, looking for places where the RGBHV signal could be swapped in, bypassing another input.

You should also be looking at schematics that do have a VGA input.

Quote:
For example, if you look at the signal flow block diagram for the HS, you will see that the HDMI sends either YCbCr or RGBHV to the cxa2171 chip. I was thinking that would be a good place to solder in the RGBHV from a VGA plug, but now I think that the chip probably looking for digital RGB and wouldn't work.


But throughout the rest of the schematic, I'm seeing many places that are labled Rin, Gin, Bin and so on.


So my question is, if I find the right place in the signal path on one of the PCB's, is it possible to add a vga/rgbhv signal that will be properly displayed by the TV?

Only if you're very lucky.


The VGA signals from the source have to be properly terminated with a 75 ohm impedance. So you cannot just inject each RGBHV signal in place of other signals.

Quote:
Or hell, there might even be a spot on the board where they have an RGBHV input but didn't actually wire it to the back of the TV for some reason. Anybody know anything that could lead me in the right direction?

Besides impedance, you're overlooking timing and signal levels. VGA timing and levels are formalized by the VESA spec.

You need to look at the signals with a 'scope.

Just matching up signals by name is not going to work.


Regards
 

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Discussion Starter · #3 ·
Thanks blue_z, I've just been inspired by other similar projects, like where people hacked an s-video output on their genesis or a VGA output on their gamecube.


I know barely anything about electronics, I've used a pencil to change the voltage for the memory in my computer, and that's about it. I just looked at the wikipedia article on impedance and it went way over my head. I'll probably do some research on that and the timings and VESA spec etc, and see if I could even approach enough knowledge to be confident enough to take a soldering iron to the PCB.
 

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Quote:
Originally Posted by CRTFTW /forum/post/19571554


I just looked at the wikipedia article on impedance and it went way over my head.

Yes, that is one complicated topic.

The 75 ohm load for video signals is usually just an LCR circuit of inductor (coil), capacitor and resistor.

Quote:
I'll probably do some research on that and the timings and VESA spec etc, and see if I could even approach enough knowledge to be confident enough to take a soldering iron to the PCB.

I'm okay working on vacuum tube audio amps which have voltages up to 500v. But TVs with several thousand volts just scares me. So learn how to safely work around high voltage devices before you ever open up your TV. You should only have to deal with the low-voltage input board, but the neck of that CRT can easily get in the way.


Regards
 

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Discussion Starter · #5 ·
Yes, I've read that the capacitors on the tube can hold a lot of volts. I will definitely read up on safety before I go in there.


A basic question before I get off to my research. Every CRT is ultimately uses RGBHV signals, right? As in, even YPbPr signals have to be changed to RGBHV before the electron guns can fire correctly?


If so... then theoretically, if I found the first spot where RGB input was required, and then sent the H and V sync signals to the correct spot (at the correct timing and voltage, of course), is there a chance it could display? Or is it completely dependent on the other processes happening throughout the PCB, which I know nothing about.


Edit: Oh crap, I think I just missed something crucial when you said "VGA signals from the source have to be properly terminated with a 75 ohm impedance". What do you mean by terminate. Is that something that happens inside the display device?
 

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Discussion Starter · #7 ·

Quote:
Originally Posted by homerging /forum/post/19572486


Buy a VGA to HDMI converter box?

Well, I'd like to avoid changing an analog signal to digital when it will just be converted right back to analog in the TV. And I don't know if a converter box will introduce any significant delay.


That said, I still might have to get one if this project turns out to be impossible.
 

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Quote:
Originally Posted by CRTFTW /forum/post/19572014


A basic question before I get off to my research. Every CRT is ultimately uses RGBHV signals, right?

If you mean color CRT, then yes.

But "RGBHV" is not actually a standardized signal, and don't expect the R, G and B signals plus the H & V sync signals internal to a TV have similar timing and levels as what is carried on a VGA cable.

Quote:
As in, even YPbPr signals have to be changed to RGBHV before the electron guns can fire correctly?

Essentially yes.

BUT your TV is not a computer monitor. The Sony is still a consumer-grade TV, and in order to keep costs low, the color CRT is bandwidth limited and uses interlaced scanning. So the internal R, G, B , H and V signals are for interlaced scanning. The VGA signal that you want to use has timing for progressive scanning. They are not compatible without conversion.

Quote:
If so... then theoretically, if I found the first spot where RGB input was required, and then sent the H and V sync signals to the correct spot (at the correct timing and voltage, of course), is there a chance it could display? Or is it completely dependent on the other processes happening throughout the PCB, which I know nothing about.

There are other factors like grounding.

I don't know about these Sonys, but an older TV that I studied had a (traditional) hot/floating chassis. All of the video and audio inputs were on one board that was properly grounded, and each signal went through an optical isolator before each isolated signal went to the hot/floating chassis. If the Sony has a similar hot/floating + grounded scheme, then the VGA connection has to be installed at the grounded input board and not to the floating chassis. It's expensive to (electrically) ground the entire TV chassis.

Quote:
Edit: Oh crap, I think I just missed something crucial when you said "VGA signals from the source have to be properly terminated with a 75 ohm impedance". What do you mean by terminate. Is that something that happens inside the display device?

Signal termination (with the proper impedance) has two main purposes. The termination circuit prevents signal reflections (back to the transmitter) or ringing which would end up looking like ghosts on video. The termination circuit also controls the power that the transmitter has to supply. The termination circuit would be right after the connector.


Again, I suggest that you try to find a schematic for a TV with a VGA input for an example of how it's done, rather than try to figure it out on your own.


Regards
 

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Discussion Starter · #10 ·

Quote:
Originally Posted by blue_z /forum/post/19573106


Essentially yes.

BUT your TV is not a computer monitor. The Sony is still a consumer-grade TV, and in order to keep costs low, the color CRT is bandwidth limited and uses interlaced scanning. So the internal R, G, B , H and V signals are for interlaced scanning. The VGA signal that you want to use has timing for progressive scanning. They are not compatible without conversion.

From what I understand, these TV's have both a 480p and 1080i native resolution. Is the internal 480p signal still interlaced somehow before it reaches the tube, or have some other timing besides 480p 60hz? I was thinking that a 480p signal coming from the transmitter (dreamcast in this case) would not need conversion.

Quote:
There are other factors like grounding.

I don't know about these Sonys, but an older TV that I studied had a (traditional) hot/floating chassis. All of the video and audio inputs were on one board that was properly grounded, and each signal went through an optical isolator before each isolated signal went to the hot/floating chassis. If the Sony has a similar hot/floating + grounded scheme, then the VGA connection has to be installed at the grounded input board and not to the floating chassis. It's expensive to (electrically) ground the entire TV chassis.

I had thought about grounding, but didn't realize that internal signals went through a different process. I'll keep this in mind going forward


Quote:
Again, I suggest that you try to find a schematic for a TV with a VGA input for an example of how it's done, rather than try to figure it out on your own.

Yeah, I've been looking at the schematic for my CRT monitor, and I'm having trouble seeing the common ground I could exploit. What would really help me would be the schematic to a CRT TV, even a CRT RPTV, that has a VGA input. They seem to be very rare though.


The only thing I've seen are some Zenith CRT's from about 10 years ago that supported 1080i or 480p and had VGA connectors. I'm trying to find a service manual, but nothing's turning up so far.
 

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Discussion Starter · #11 ·
Ok blue_z, hope you're still here, I followed your advice and I think I might have found a way to do this!


It seems Sony produced some HDTV CRT sets in Australia that had RGBHV rca inputs for use with DTV players at the time. The input could also accept YPbPr. Here is the schematic of the video switch chip with the RGBHV input highlighted:




Keep in mind, these video switch chips are the first components to receive the signals from the rear panel.


Now look at the block diagram for my TV, the 30hs420, and its block diagram, showing the type of signals the HDMI will send its video switch. This is the diagram that gave me this idea in the first place.




IN2 is the input for the two component inputs, IN3 is the HDMI with RGBHV listed as one of the possible signals.


And here is the actual schematic of the chip. Notice the H and V inputs accompanying all the YPbPr inputs (just as in the Austrailian TV that actually has RGBHV).




So the HDMI H and V has nothing attatched (calling into question the block diagram, which has other mistakes), but the inputs are there. Also, there is a completely unused set of inputs with H and V in the upper left (a possible independent input?!), though they seem to be grounded for some reason.


And lastly... if you look at the PDF I attached, it has a diagram that includes both chips, and if I'm reading it correctly the chip in my TV (CXA2171AQ) should be able to detect and properly sync with RGBHV signals! Then its only a matter of whether or not the chips further down the line can manage the signal


So here is my hypothesis: If I can attach the RGBHV and GND of a vga plug into IN1 of the CXA2171AQ chip (properly terminated and all that stuff), and I can find a way to trick the TV into looking for the signal (substituting the RGBHV for one of the unused composite or S-video channels) then I will have a fully operational RGBHV input for my TV! (Alternative hypothesis: Just substitute the RGBHV in the HDMI pathway)


So... please tell me what I'm missing here. If the chip has the capability to read the signal, then I should be able to make it work... right?


If any of you would like to look at the user or service manuals for either of these sets, just let me know.



 

cxa2239r.pdf 68.1494140625k . file
 

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Discussion Starter · #13 ·

Quote:
Originally Posted by homerging /forum/post/19661353


Correct, the HR series had RGBHV:
http://vhd.co.kr/ct/file/db/bk2.jpg
http://users.tpg.com.au/jbrogan/


I think it autodetects whether there is ypbpr or RGBHV being given to the input by whether or not anything is being given to the HD / VD RCA plugs.

yeah, that's what I figured. The question is whether the chip in the HS series will perform in the same way as the HR series when presented with RGBHV. I'm thinking it will, it's just sony never actually took advantage of the feature.



I really want to give this a try, there are just so many things I'm confused about. Like, why are some of the pins on IN1 grounded? That seems pointless.
 

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Quote:
Originally Posted by CRTFTW /forum/post/19662645


.....I really want to give this a try, there are just so many things I'm confused about. Like, why are some of the pins on IN1 grounded? That seems pointless.

The IN1 input is not used and therefore will not be selectable by the normal INPUT selection of the tv. As for the grounded IN1 pins, it would be common design practice to protect the chip's circuit from stray input signals by grounding the unused input's pins. Those same pins for the IN2 and IN3 are also grounded/stabilized by a cap.


IMO, you will have a better chance of success with this endeavor if you choose either the IN2 or IN3 inputs to this chip, as they are the only ones currently selectable by the set. As other posters have indicated, this is NOT a simple task. The process of choosing an appropriate location and soldering wires will be very difficult. IMO, you must consider whether your level of electronics expertise is up to this task before hitting the M board with a soldering iron. You may find yourself with an unusable board.
 

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Discussion Starter · #15 ·
Quote:
Originally Posted by raouliii
IMO, you must consider whether your level of electronics expertise is up to this task before hitting the M board with a soldering iron. You may find yourself with an unusable board.
For sure, that's why I'm asking lots of questions. I'm also hoping to find someone knowledgeable who's interested and could help walk me through it.


As for IN1, I was hoping I could get it to be selectable from either a service menu adjustment, ideally, or rewiring the pins that are responsible for switching inputs. Also, even though the schematic seems to say something different, the block diagram says that the converted composite/s-video signals go to IN4, making a third currently selectable input. I still need to look into that though, I'm having trouble finding where the Y/C inputs go after they're converted to YPbPr... if they are converted. I don't know, the block diagram could be totally wrong... or the schematic could be wrong, or both.


As for appropriate location for soldering, i was thinking as long as I found out how to ground and terminate the signal properly, the CXA2171AQ chip would be the place to solder. I know the CXA2189Q chip accepts the signals directly from the inputs. But the CXA2171AQ has the component ins coming from a a small selector chip on the U board (which then attach directly to the inputs), which switches between the two. So what I need to know is if the YPbPr signals coming out of that small chip are the same level as the signal going in. I have a voltmeter, but I think I'm going to need more hardware to find out for myself.
 

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Quote:
Originally Posted by CRTFTW
.....As for IN1, I was hoping I could get it to be selectable from either a service menu adjustment, ideally, or rewiring the pins that are responsible for switching inputs.
That would be a tough one. A question: Do you expect to have any or all of the existing inputs to continue to function, or will this mod result in a vga input only operation?
Quote:
Originally Posted by CRTFTW
.....Also, even though the schematic seems to say something different, the block diagram says that the converted composite/s-video signals go to IN4, making a third currently selectable input.
I would hazard a guess that IN4, since it is sourced from the Sub Chroma Decoder, is used for v1,v2,v3,v4 twin view only, since it bypasses DRC, which is applied to all SD inputs for main (normal) display. Furthermore, the twin view on these sets have a limitation that v5/v6 and v7 inputs are only able to be displayed in one window only of the twin view function, therefore, I would guess that CXA2171 is the source of that twin view window.
 

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Discussion Starter · #17 ·
Quote:
Originally Posted by raouliii
That would be a tough one. A question: Do you expect to have any or all of the existing inputs to continue to function, or will this mod result in a vga input only operation?
I was hoping to be able to do it with only losing the SD inputs, and maybe installing a hard switch for when I want to use a Y/C source. So basically getting the TV to display IN1 from CXA2171 when I select v1 or something.

Quote:
Originally Posted by raouliii
I would hazard a guess that IN4, since it is sourced from the Sub Chroma Decoder, is used for v1,v2,v3,v4 twin view only, since it bypasses DRC, which is applied to all SD inputs for main (normal) display. Furthermore, the twin view on these sets have a limitation that v5/v6 and v7 inputs are only able to be displayed in one window only of the twin view function, therefore, I would guess that CXA2171 is the source of that twin view window.
Ok, on second look at the block diagram, I see why you would say that. That could complicate my idea from the first part of this post, as the TV may not be looking to the CXA2171 for a signal. But then again, I don't think my TV has the twin-view function... so maybe it's for a different reason?
 

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IMO, the most likely scenario for success will be to give up either v7 (IN3) or v5/6(IN2) and attempt the connection of the rgbhv there.


For twin view sets, IN4 is the SD input to the CXA2171 chip. Even if you could fool your hs420 into thinking it was a twin view set, the IN4 input would likely only be routed for twin view use.


Forcing a selection of IN1, will be difficult without having a full understanding of how the select lines are implemented. I have never been able to find a datasheet for the CXA2171. BTW, on ATSC tuner equipped sets, IN1 is used for the ATSC sourced video.
 

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Discussion Starter · #19 ·
You're right that v5-v7 are the best bets. I just wish I could have a fourth HD input. Maybe I can look at data sheets for the other video switches in the family and see how the select lines work in those. I've had no luck finding the sheet for CXA2171 either.


I was thinking that there was a simple pin that accepted the "ON" signal for a given input, but now that I look at the chip again, it's probably not that simple.
 
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