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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Sat Aug 22, 2020 3:12 am 


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Alright, let us know how you get on, then.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Fri Aug 28, 2020 12:51 pm 



Joined: 07 Aug 2018
Posts: 25
So I have an MX7000 where the picture is not really that great anymore and decided to gut it for its speakers. But before that I decided to do the experiment of changing the G1 voltage and see if it does anything to the spot size.

So I did the following:

Image

I removed the one leg of R19 from the circuit and hooked up two power supplies in series in order to get up to -60V. My setup looks like this:

Image

First I did a control with 0V. I hooked up my SNES to the MX7000 and fired up 240p test suite.

Image

Then I raised the voltage. As expected the picture got darker so I had to adjust G2 in order to maintain the same brightness. It was difficult to always get right though. Here a picture of -30V:

Image

After that I raised the voltage to the maximum I'm able to (-60V) and raised G2 as well:

Image

To be honest I don't see a difference. The spot size does change when you raise G1 but that is, in my opinion, solely due to the lower brightness. You'll have the same effect by just lowering the brightness. When I raise G2 to reach the same brightness the spot size gets bigger again. Oh and changing the focus voltage will not improve that.

The biggest problem with this TV though is I can not change the cutoff. Maybe there might be an improvement if the cutoff is changed but I'm not sure. There is a cutoff option in the service menu but is somehow does not have any effect at all. And there are not pots on the circuit board whatsoever. That is actually the reason why I will gut the MX7000 as the picture has a red tint.

If I get my hands on another TV that I'm willing to sacrifice for the experiment I'll give it another shot.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Tue Sep 08, 2020 2:56 am 



Joined: 17 Aug 2020
Posts: 81
Did you confirm with an oscope that the G1 voltage does not have any ripple? In both LTSpice simulations and in real life, I had to add a film cap on the G1 to keep the 5pF cathode to anode capacitance from inducing ripple on the G1. Maybe my power supply is shitty, I dunno, but the film cap made the G1 voltage nice and smooth. From my experiments, -60 volts on a consumer CRT is likely going to get a 12.5% reduction in spot size at matching black levels, which is going to be very hard to notice. I found that you need at least around -121 volts to get a roughly 25% reduction in spot size. See details below...

Finally a 3 day weekend, so I got some time to experiment with different negative G1 voltages. As the slides in the original post stated, as the G1 is made more negative, G2 and cathode cutoff voltages have to be tuned to get properly calibrated black levels. I made sure to calibrate for matching black levels, which is a real pain in the ass and time consuming. At G1 voltages of 0 to -30, I noticed no difference in spot size, if black levels were properly calibrated. I started to see about a 25% reduction in spot size around G1 of -100 to -121 volts. My shitty no-name bench power supply maxes out at 121 volts, so I couldn't try for smaller spot sizes. I am going to build a power supply around a 21st Century Maida High Regulator, which will allow me to experiment with G1 voltages of up to -500 volts.

Also, I did this experiment using a consumer CRT: 27-inch Panasonic CT-27L8G. For a display pattern, I used a Playstation playing Castlevania Symphony of the Night over S-video. This TV's component is broken, so S-video was the best I could do. As spot size got smaller, it became more obvious that my CRT's converge is way off for a smaller spot size (see pics below).

First, I simulated in LTSpice, which made it clear that I'd need a few diodes to prevent my crappy no-name bench power supply from getting fried by negative voltage. LTSpice also made it clear that I'd need capacitor C9, because otherwise the G1 voltage would oscillate due to the 5pF capacitance between the cathodes and G1 and the fluctuating voltage on the cathodes due to the amplified RGB signal. I used a 250V 3.3uF film capacitor I had lying around, and in both LTSPice and in real life, it made the G1 voltage super smooth.
Image
Image


Playstation Castlevania SoTN over S-Video

Alucard's cloak pulses red on the inside, which in hindsight was a terrible thing to use as a benchmark. Next time I will change Alucard's gear to be something static.

As the literature in the original post states, the specs for the "spot size to G1 curve" and the "G2 to G1 curve" are dependent on the electron gun's design. Professional CRTs use a much smaller hole in the exiting end of the G1 anode, so the default size of the electromagnetic iris already very small. A more negative voltage for such gun designs will decrease spot size faster than the electron gun design in a consumer CRT because a consumer CRT's G1 anode's exit hole is larger... and an electromagnetic field's strength follows an inverse square law. In other words, it is going to take more than -121 volts to cut the spot size in half.

For this 27-inch consumer CRT, a G1 of -300 volts will be needed to get half the spot size. Also, I am going to have to pull out my convergence gauge because at a smaller spot size, it is clear that convergence is not perfect. Now to build a Maida regulator so I can experiment with more extreme negative voltages.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Tue Sep 08, 2020 3:24 am 


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nice progress


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Tue Sep 08, 2020 1:48 pm 



Joined: 07 Aug 2006
Posts: 507
Location: Sydney, Australia
LukeEvansSimon,

You've somehow got it quite wrong. On a CRT it's the potential difference between the grid and cathode that controls the amount of electrons shooting towards the phosphor. When you change the DC potential on G1 grid with respect to the cathode, all you are doing is changing the bias. You can achieve exact same thing by turning down the brightness with the remote control. This will change the DC level on the cathode instead.

Your fundamental error seems to be that you attach significance to the potential difference between ground and the G1 grid. The CRT doesn't care - it doesn't have a ground connection. It's only the potential difference between cathode and grid that matters. Very old television sets would drive colour difference signals into the three cathodes and Y into G1 and do the colour difference to RGB conversion inside the picture tube itself (the earliest colour sets had a separate set of grids for each cathode). More modern ones just tie the G1 grid to ground as there really isn't anything interesting to do with it when the jungle IC can easily manipulate the amplitude and bias of the signal RGB signals going to each cathode.

With that out of the way, the control for changing the beam size is called focus. You can usually find it on the side of the line output transformer. If you have adjusted the focus and turned the contrast down (to reduce bloom) and you still are unhappy with the beam width then the only way to improve it is to replace the picture tube with a higher resolution one.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Tue Sep 08, 2020 4:33 pm 



Joined: 17 Aug 2020
Posts: 81
viletim wrote:
LukeEvansSimon,

You've somehow got it quite wrong. On a CRT it's the potential difference between the grid and cathode that controls the amount of electrons shooting towards the phosphor. When you change the DC potential on G1 grid with respect to the cathode, all you are doing is changing the bias. You can achieve exact same thing by turning down the brightness with the remote control. This will change the DC level on the cathode instead.

Your fundamental error seems to be that you attach significance to the potential difference between ground and the G1 grid. The CRT doesn't care - it doesn't have a ground connection. It's only the potential difference between cathode and grid that matters. Very old television sets would drive colour difference signals into the three cathodes and Y into G1 and do the colour difference to RGB conversion inside the picture tube itself (the earliest colour sets had a separate set of grids for each cathode). More modern ones just tie the G1 grid to ground as there really isn't anything interesting to do with it when the jungle IC can easily manipulate the amplitude and bias of the signal RGB signals going to each cathode.

With that out of the way, the control for changing the beam size is called focus. You can usually find it on the side of the line output transformer. If you have adjusted the focus and turned the contrast down (to reduce bloom) and you still are unhappy with the beam width then the only way to improve it is to replace the picture tube with a higher resolution one.


TLDR: voltage is relative, but we are dealing with analog electronics and so the position and shape of the G1 anode creates an EMF that acts as an iris, constricting the electron beam to be a tighter, smaller spot size.

Yes, I understand that voltage is relative to another point of measure. I am assuming cathodes and anodes are all relative to chassis ground. The thing you are failing to acknowledge is that the shape and positioning of the cathodes and anodes matters. There is a reason that the G1 anode is shaped like a tube with a small hole at the end pointing towards the screen, as described in Display Designs Inc slides.

Yes, the G1 does impact cutoff and brightness, as described at length in the articles that I linked in the OP, but what is important is that it also acts as an iris because of the small aperture at the end of the G1. We are dealing with analog electronics here. The G1 does not have a point voltage. It has an electromagnetic field within and around it, and this electromagnetic field has a shape. The electrons in the beam are repelled by the relative negative voltage of the electromagnetic field surrounding the G1 anode, and sense the G1 anode is a tube with a small hole on the end that faces the screen, this causes the electron beam to squeeze through the G1's hole. As the G1's charge becomes more negative, it causes the electromagnetic field at the G1's hole to become more intense. The intensity of the electromagnetic field follows an inverse square law based off of the distance from the edge of the G1's hole to the center of the hole. In other words, the voltage at the edge of the G1's aperture is more negative than the voltage at the center of the aperture. This causes the electromagnetic field at the aperture of the G1 tube to act as an iris. The CRT Display Designs slides diagram the impact of this electromagnetic field:
Image

The use of cathode to G1 and G1 to G2 voltages to tune for a smaller spot size is also described on page 3 here. This article mentions that directly increasing cathode voltage (as opposed to directly manipulating G1), places a greater demand on the RGB amplifiers that drive the cathodes. The mod that I am describing takes a shortcut by directly charging the G1 anode and it has the benefit of not placing a greater burden on the RGB amplifiers, because it does not change the voltage across the NPN transistors used for RGB amplification. So yes, this mod could be accomplished by replacing the RGB amps with higher voltage rated amps, then modifying the chassis to increase the voltage across these amps, and also increase the G2 voltage correspondingly. However, I have searched Mouser and Digikey for NPN transistors with matching bandwidth and a higher voltage rating, and I could not find any that would allow for a considerable increase in voltage amplification. The reason why some older CRT TVs used color differencing for varying the G1 voltage is because older NPN transistors could not handle the same magnitude of voltage amplification as modern NPN transistors. Directly charging the G1 is an easier mod, does not place a higher burden on the NPN transistors, and the changes are localized to attaching a negative voltage rail to the G1:
Image

Finally, regarding your comments on the focus anode, yes it does impact spot size, as well as spot focus. It is positioned and shaped in the electron gun to act like an electromagnetic lens (as opposed to an electromagnetic iris). The focus anode is positively charged relative to the cathodes, unlike the G1, which is negative charged relative to the cathodes. The focus anode also has a different shape, which means its electromagnetic field has a different shape.

There is a reason why traditional optical systems use both an iris and a lens. Both iris and lens impact spot size and spot focus on the light that passes through them. The same holds for an electron gun, but the iris and lens are electromagnetic fields. The iris has a large impact on spot size, and a small impact on spot focus. The lens has a small impact on spot size and a large impact on spot focus. The iris has a small impact on brightness, but the accelerator anode G2 has a large impact on brightness. In analog devices, none of these things are decoupled from each other, but each of them are included in a CRT for because they each have a different impact on spot size, spot focus, and brightness.

If consumer CRT TVs could accomplish spot size adjustment without the use of a G1 anode, then why would manufacturers continue to include it in their electron guns? Are all of the documents that I referenced, are all of the people that wrote them wrong about K to G1 and G1 to G2 voltages impacting spot size wrong?


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Tue Sep 08, 2020 8:09 pm 



Joined: 17 Aug 2020
Posts: 81
viletim wrote:
LukeEvansSimon,

You've somehow got it quite wrong. On a CRT it's the potential difference between the grid and cathode that controls the amount of electrons shooting towards the phosphor. When you change the DC potential on G1 grid with respect to the cathode, all you are doing is changing the bias. You can achieve exact same thing by turning down the brightness with the remote control. This will change the DC level on the cathode instead.

Your fundamental error seems to be that you attach significance to the potential difference between ground and the G1 grid. The CRT doesn't care - it doesn't have a ground connection. It's only the potential difference between cathode and grid that matters. Very old television sets would drive colour difference signals into the three cathodes and Y into G1 and do the colour difference to RGB conversion inside the picture tube itself (the earliest colour sets had a separate set of grids for each cathode). More modern ones just tie the G1 grid to ground as there really isn't anything interesting to do with it when the jungle IC can easily manipulate the amplitude and bias of the signal RGB signals going to each cathode.


Using a TV's brightness controls to increase DC bias on the cathodes does decrease total brightness, but it does not increase the DC bias of the G2 anode. Similarly, using the flyback screen knob to decrease the DC bias on the G2 anode does not decrease the DC bias of the cathodes anode, but it does decrease total brightness. The mod I am talking about involves both increasing cathode to G1 by a few hundreds volts and increase G2 to G1 by a few hundred volts. Tell me how you are going to accomplish this using a remote control? You are confusing different mechanisms for decreasing brightness, which are not all equivalent. If you can accomplish this using your remote control, then post pictures of a multimeter showing so.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Wed Sep 09, 2020 1:57 am 



Joined: 07 Aug 2006
Posts: 507
Location: Sydney, Australia
LukeEvansSimon,

Maybe you're right...

To make your grid G1 voltage, since you don't need much current, you can add another secondary winding to the exposed core of the line output transformer. Then a diode + cap to make it DC. You get about 2V per turn this way.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Wed Sep 09, 2020 5:38 pm 



Joined: 17 Aug 2020
Posts: 81
viletim wrote:
LukeEvansSimon,

Maybe you're right...

To make your grid G1 voltage, since you don't need much current, you can add another secondary winding to the exposed core of the line output transformer. Then a diode + cap to make it DC. You get about 2V per turn this way.


That sounds like a much lower cost mod. I've never wound my own transformer before, but I will look into it. Thanks for the suggestion. At some point, the breakdown voltage between the cathodes and G1 and the G1 will get hit and arcing will occur. If I can't get a convincing side-by-side with matching black-levels and a 50% reduction in spot size, then I am going to declare the experiment a failure and move on.

I scoped my TV's cathodes to see if there was any headroom to increase DC bias of the cathodes and increase G2 voltage (the remote control approach to calibrating for a smaller spot size). The chassis design in my CRT TV allows for the RGB signal to peak at about 220 volts without clipping, but the service manual describes not going above 200 volts for cathode cutoff so that during horizontal blanking the cathode voltage can go above 200 volts for blacker than black retracing (this prevents retrace lines). In other words, there is almost no headroom to increase cathode voltage through service menu changes, without clipping the RGB signal and crushing black levels.

Another way (that does not make an analogy with an iris) to explain why the OP mod will help decrease spot size is the G2 anode is used for particle acceleration (particles are the electrons that make up the cathode ray). The greater the G2, the greater the acceleration of the electrons towards the screen. This gives electrons that are not moving straight towards the screen less time to spread out before they impact the phosphor on the screen, and so this helps decrease spot size. However, since this is an analog device, higher G2 voltage does not just increase electron acceleration, it also changes black levels. Proper black levels can either be obtained by increasing DC bias on the cathodes or by decreasing G1 voltage.

As spot size gets smaller, it is to be expected that the perceived brightness is lower even though black levels are properly calibrated. This is a known attribute of CRTs displaying 240p content. Professional CRTs with a very small spot size (what gamers refer to as "high TVL") are perceived as "darker", even when black levels are properly calibrated. This brings up the problem with gamer community terminology where "brightness" and "black levels" are used interchangeably.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Fri Sep 11, 2020 10:56 pm 



Joined: 17 Aug 2020
Posts: 81
Partial Success
Charging G1 to -243 volts, and increasing G2 voltage to properly calibrate black levels seems to have cut spot size in half on my consumer CRT TV, a 27-inch Panasonic CT-27L8G, but this mod still needs improvements due to an issue that was mentioned in the literature, but wasn't clear until I ran this experiment. Details below the side-by-side.

Playstation Castlevania SoTN over S-Video


Red and Blue Color Bleeding Problem
Now for the problem that the literature called out but was only obvious when running this experiment. As mentioned in the TI paper, the variation in cut off voltages for each cathode starts to diverge as the voltage difference between G2 and G1 is increased, and this is clear from the screenshot where the cut off bias for red is not high enough and so the reds are bleeding outside the small spot size. Similarly blue's cut off voltage is not high enough and is bleeding a little bit. This is why the smaller spot size is only obvious for the green parts of the image. Luckily, this consumer CRT's service menu allows for setting the cut off voltage for each cathode separately. Hopefully this gets the red and blue spot size to match the spot size of green, which will make the righthand side picture much better and it will make the spot size reduction much more obvious.
Image

Spot Size Can Be Smaller Than Dot Pitch
One last thing, surprisingly, the dot pitch of the slot masks doesn't appear to be a bottleneck on spot size. Look at the tile pattern at the top of my crappy iphone photos of the side-by-side. The green cathode's cutoff voltage is properly set, so green colors don't have the bleeding issue that blue and red have. All of the green colored parts of the image have a tiny spot size and the spot size for darker greens is much smaller than the size of a single slot in the slot mask. Full bright green appears to take up one full slot in the slot mask.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Sat Sep 12, 2020 12:40 am 



Joined: 17 Aug 2020
Posts: 81
Green Gun Only
Since the red and blue color bleeding issue mentioned earlier makes it hard to see the magnitude of the spot size reduction, I made a side-by-side with the red and blue colors disabled. To those claiming this is just reducing the brightness: the smaller spot size may look "less bright", but again, black levels are matching between left and right image. The "less bright" look is for the same reason that "high TVL CRTs make games look darker" phenomenon. Literally less phosphor area is being illuminated because of the smaller spot size obtained in this experiment, just like high TVL CRTs illuminate less phosphor area for 240p content.



Filtering to green only makes one other issue with this mod stick out. Phosphor blooming. Look closely in the right-hand-side image, where the pixels are the brightest, the corresponding phosphors bloom very large to the point where spot size reduction does not hit the full 50% reduction. I am not sure if this is due to a lack of adequate voltage regulation, or if this is due to the large dot pitch of slot mask consumer CRTs.

Next Steps
Fix red and blue bleeding: try to tune cathode cut off voltages for red and blue, and possibly also adjust convergence of red and blue. I've got to do dinner with the wifey and the kiddos, so hopefully I can get free time late tonight or this weekend.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Sun Sep 13, 2020 12:41 am 



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Wow! I didn't know dot size was adjustable from an electric standpoint. I just assumed that it was determined by physical factors only. But it does make sense.

I've tossed around the idea of messing with the horizontal refresh. I could be way, far in another galaxy off on this, but my theory is that if you could find a way to keep the TV doing it's own vertical sync and RGB and all, which I suppose there's a separate coil for vertical aiming of the electron guns. But then disconnect from the neck the horizontal coil and and hook up another circuit to it to do the horizontal positioning. Maybe something out of a VGA monitor or something. That way you could switch between the TV's own 480i/240p horizontal refresh, and then switch to a 480p or maybe even a 720p horizontal refresh since the vertical sync (using same starting line in a 240p fashion) and the RGB should all be the same.

This dot shrinking technique could help with a 720p picture.

Man! If I could impliment this dot sizing and a 480p or 720p horizontal refresh into my 27inch Sony Trinitron SD consumer TV, that would be far more than I could ever ask for!


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Sun Sep 13, 2020 12:51 am 



Joined: 17 Aug 2020
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Issac Zachary wrote:
Wow! I didn't know dot size was adjustable from an electric standpoint. I just assumed that it was determined by physical factors only. But it does make sense.

I've tossed around the idea of messing with the horizontal refresh. I could be way, far in another galaxy off on this, but my theory is that if you could find a way to keep the TV doing it's own vertical sync and RGB and all, which I suppose there's a separate coil for vertical aiming of the electron guns. But then disconnect from the neck the horizontal coil and and hook up another circuit to it to do the horizontal positioning. Maybe something out of a VGA monitor or something. That way you could switch between the TV's own 480i/240p horizontal refresh, and then switch to a 480p or maybe even a 720p horizontal refresh since the vertical sync (using same starting line in a 240p fashion) and the RGB should all be the same.

This dot shrinking technique could help with a 720p picture.

Man! If I could impliment this dot sizing and a 480p or 720p horizontal refresh into my 27inch Sony Trinitron SD consumer TV, that would be far more than I could ever ask for!


I was also thinking about changing horizontal frequency as a cool mod, but I think it would be quite an extensive change. It would be cool if some company made an upgrade circuit board for a few of the common consumer CRT TV lines, which had built in support for true multi-sync like you stated and also spot size adjustment and native RGB.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Sun Sep 13, 2020 2:29 am 



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LukeEvansSimon wrote:
I was also thinking about changing horizontal frequency as a cool mod, but I think it would be quite an extensive change. It would be cool if some company made an upgrade circuit board for a few of the common consumer CRT TV lines, which had built in support for true multi-sync like you stated and also spot size adjustment and native RGB.

I'm far from an expert, but a univesal board should be possible. It may need a lot of adjustment knobs or what not. But add to those the ability to do other frequencies such as 50hz PAL and SECAM, or maybe even take a digital signal and run G-sync at an even higher refresh, like 120HZ or 240HZ, or something like that. The possibilities could be endless...


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Sun Sep 13, 2020 5:20 pm 



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LukeEvansSimon wrote:
Phosphor blooming. Look closely in the right-hand-side image, where the pixels are the brightest, the corresponding phosphors bloom very large to the point where spot size reduction does not hit the full 50% reduction. I am not sure if this is due to a lack of adequate voltage regulation, or if this is due to the large dot pitch of slot mask consumer CRTs.

Would it be possible to mod in a voltage regulator like the Sony KV-27FV310 has? That would prevent a consumer CRT from blooming and become sharper with more defined scanlines.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Sun Sep 13, 2020 5:33 pm 


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Quote:
Man! If I could impliment this dot sizing and a 480p or 720p horizontal refresh into my 27inch Sony Trinitron SD consumer TV, that would be far more than I could ever ask for!


As I understand it, in Wells Gardner arcade monitor CRTs the deflection yoke must be designed for 15, 25, or 31Khz if you want to connect to a chassis that supports those frequencies. From what I gather, even though the tubes are largely interchangeable, you cant use std res. yoke with a med. or high res chassis. Im not sure why that is other than higher voltages may be needed to deflect higher frequency scan rates-- if thats the reason why, then the yoke must be designed to handle those higher voltages/frequencies or then you risk burning the yoke or the chassis board.

So dont get too excited just yet...


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Mon Sep 14, 2020 12:52 pm 



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I'm interested in the before and after images for a solid green raster before and after the mod (as opposed to in game).


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Tue Sep 15, 2020 2:32 am 



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Open source high voltage regulators are available (such as the Maida). I am not sure where Sony’s FV310 uses its high voltage regulator. Is it for B+ voltage? G2 voltage? I was thinking that the voltage is dipping towards zero for the G1 anode, which causes the spot size to increase for just the region of the very bright pixels. I have a 3.3uF film cap that I put on the G1, which in LTspice simulations fixed the issue. I need to oscope my prototype to see if G1 voltage is fluctuating.

It could be G2 voltage is dipping. It may not be obvious, but this mod involves cranking the G2 voltage up my a few hundred volts relative to ground. G2 comes straight off the flyback and so it is unregulated and if it dips for a few microseconds, that may cause the spot to bloom a bit. I ordered a high voltage oscope probe that I will use to check what is happening to G2 voltage.

I like to think of the smaller spot size as being due to the highly negative G1 voltage “closing” the electromagnetic iris and the increased G2 voltage increases the acceleration of the electron beam, which gives it less time to spread out before it hits the phosphor. When the beam is brighter it is because more electrons are flowing through the beam. This can cause the charges in the other anodes to fluctuate as the beam passes through the anodes, which momentarily opens the iris a bit and slows the beam momentarily a bit.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Mon Sep 21, 2020 11:57 pm 



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thumptech wrote:
I'm interested in the before and after images for a solid green raster before and after the mod (as opposed to in game).


Here is a solid green screen in 240p Test Suite on a 2-chip SNES over component. Hopefully this makes it clear that this mod really does allow for controlling the spot size. Left is G1 anode at 0 volts, and right is G1 anode at -244 volts and G2 anode voltage is increased (using the screen pot on the flyback) to calibrate black levels. Shitty pictures taken by a hand held iphone. I should have cleaned the CRT's screen too.
Image

After tuning the cutoffs, here is what the game looks like side by side, with left G1 anode at 0 volts, and right is G1 anode at -244 volts and G2 anode voltage is increased to calibrate black levels. Sorry for the glare right down the center of the image.
Image

An even more negative voltage would have produced an even smaller spot size. To recap the two things this mod changes within the electron gun: (i) first it shrinks the size of the electromagnetic iris induced by the cathode - G1 voltage, and (ii) it dramatically increases the acceleration of electrons that pass through the iris by a significant increase in the G2 - G1 voltage. Both of these increases in voltage differential shrinks the spot size, which demonstrates that the main cause of "thick scanlines" is due to a small spot size.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Tue Sep 22, 2020 9:20 am 


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LukeEvansSimon wrote:
(ii) it dramatically increases the acceleration of electrons that pass through the iris by a significant increase in the G2 - G1 voltage.

Doesn't that also increase the amount of X-Rays generated by the CRT?
_________________
GCVideo releases: https://github.com/ikorb/gcvideo/releases


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Tue Sep 22, 2020 10:39 am 


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Ok, that looks like a pretty impressive result, and that's some amazing work. I apologise for being skeptical, i didn't find your initial posts easy to follow.

I do have a few follow up questions:

1. Can you pretty please write out a more concise guide to what you're doing, step by step, without so many external references? What needs disconnecting (the sets original G1 connection?) what needs connecting to what, and what doesn't need touching, etc.

2. What is this doing to x-ray production? I'm not meaning to be a downer, but you're putting more energy into the system, and like with the normal operation of a CRT, not all that energy will come out as visible light. I have one of those cheap ionising radiation sensors, and was planning to test this out. (assuming i can find a source of 200+VDC as required).

EDIT: lol, ninja'd by unseen on the xray production question ;)


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Tue Sep 22, 2020 10:47 am 



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Okay...time to get a HV supply. :D

I got a 100Hz Sony I can sacrifice for further testing.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Tue Sep 22, 2020 11:01 am 



Joined: 02 May 2017
Posts: 5
LukeEvansSimon wrote:
thumptech wrote:
I'm interested in the before and after images for a solid green raster before and after the mod (as opposed to in game).


Here is a solid green screen in 240p Test Suite on a 2-chip SNES over component. Hopefully this makes it clear that this mod really does allow for controlling the spot size. Left is G1 anode at 0 volts, and right is G1 anode at -244 volts and G2 anode voltage is increased (using the screen pot on the flyback) to calibrate black levels. Shitty pictures taken by a hand held iphone. I should have cleaned the CRT's screen too.


Thankyou! This is exactly what I believe many people wanted to see. I was skeptical but I think i will try this on the bench at some stage. It should be possbile with a isolation transformer, a variac and a rectifier.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Tue Sep 22, 2020 5:02 pm 



Joined: 17 Aug 2020
Posts: 81
I shared all of the background research to show this community that there are many books and docs out there that are rotting away and likely soon to be lost. Service manuals, industry research presentations, books, papers, you name it. Lots of CRT knowledge is out there and getting deleted each day.

Regarding x-rays, I did not measure. If somebody has a meter, please measure x-ray output. I bet x-ray production is not an issue as the big concern around x-ray production is due to the anode cap voltage going too high. The approximately 25,000 volts anode is the final accelerator, and if its voltage is too high, a very small amount of x-rays may be produced by the CRT. The G2-G1 voltage is the differential that causes the initial acceleration of electrons, which are literally standing still at the cathode to G1 anode, when black is displayed.

It would be great to see more community buy-in for this mod. I have a dozen responsibilities between wife, kids, and work, so this mod will evolve faster if more people experiment in this area. Things that need to be tried:



Last edited by LukeEvansSimon on Tue Sep 22, 2020 5:35 pm, edited 1 time in total.

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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Tue Sep 22, 2020 5:05 pm 



Joined: 17 Aug 2020
Posts: 81
One last thing that this mod does: it makes it easier to get both the corners and the center of the screen into focus at the same time. This is likely due to the "depth of field" effect of the electromagnetic iris being smaller.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Wed Sep 23, 2020 9:55 am 



Joined: 17 Mar 2018
Posts: 121
Very cool progress!
I'm sure we could get a hold of a N5 or N6 PVM for testing. I'll have to stay in touch with ElBartoME concerning the topic :)


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Wed Sep 23, 2020 4:55 pm 



Joined: 07 Aug 2018
Posts: 25
I have a 14N2 that won't power on. If I can figure out the problem and fix it I'm willing to sacrifice it for the test.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Wed Sep 23, 2020 5:15 pm 



Joined: 17 Aug 2020
Posts: 81
ElBartoME wrote:
I have a 14N2 that won't power on. If I can figure out the problem and fix it I'm willing to sacrifice it for the test.


I bet seeing side-by-sides on a 600 TVL PVM will dramatically improve popularity of this mod. For many, the 600 TVL look is just a bit shy of what they want out of a PVM, and a pot for allowing the user to tweak TVL to their taste would dramatically improve popularity of these "lower end" PVMs. The fact that this mod produced visible results for a cheapy, heavily used curved slot mask consumer CRT TV makes me confident that the results on a PVM will be insanely good.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Wed Sep 23, 2020 5:26 pm 


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Still a bit confused over calling this "higher TVL". Its not changing the TVL at all. There are still the same number of horizontal dots in a given length in the pre- and post mod pictures you have shown. This seems to only be increasing beam focus or decreasing the vertical height of each pixel.


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 Post subject: Re: Mod a consumer CRT television to make it high TVL
PostPosted: Wed Sep 23, 2020 7:16 pm 



Joined: 17 Aug 2020
Posts: 81
Josh128 wrote:
Still a bit confused over calling this "higher TVL". Its not changing the TVL at all. There are still the same number of horizontal dots in a given length in the pre- and post mod pictures you have shown. This seems to only be increasing beam focus or decreasing the vertical height of each pixel.


I think you are thinking of slots in the mask as being analogous to pixels, which is wrong. CRTs are analog video devices, so mask dot pitch is one of 3 factors that can bottleneck resolvable TVL. Resolvable TVL is determined by: RGB amplification bandwidth, spot size, and mask dot pitch. On most CRTs, the bottleneck is spot size, not dot pitch of the mask and definitely not amp bandwidth. Before the mod, spot size is 2x the dot pitch. After the mod, spot size is matching the dot pitch in size. So a line of 4 consecutive slots in the mask will have no black slots between two white spots because the spot size takes up 2 slots, and after the mod, a spot only illuminates a single slot:


TVL is also a stupid metric that was clearly designed for marketing purposes as opposed to properly informing people about a display's properties. Gamers prefer high TVL, not because of the ability to alternative more vertical white and black lines within a region the same width as the height of the CRT. They like higher TVL because of the smaller spot size that creates both a sharper image and thicker scan lines.


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