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trebortaergeht
Joined: 14 Apr 2010
Posts: 73
Location: California
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| Posted: Sat Jul 23, 2011 5:56 pm Post subject: CRT electronic design theory questions |
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This question is more about direct view displays but the electronics for all crts are similar, plus the CRT is "projecting" it's light into your eyes anyway.
On to the topic, I recently obtained a whole bunch of arcde cabinets for extremely cheap but all of them have no monitors or bad monitors. I have already obtained a bunch of crts free off craigslist but only one of them was able to be modified for rgb.
All of the others have no rgb all the way to the neckboards where the signals become rgb at the amplifier so I need to rebuild the neckboards.
Since I have to redesign the neckboards anyway I was thinking of just completely redoing the electronics to be suitable for arcade use and making them tri-mode to support most arcade boards. I've already think I've worked out how the input stages for the horizontal and vertical deflection would work. All of he chip datasheets I've seen seem to have a horizontal oscillator driven by a crystal at the horizontal scanning and syncs to the input horizontal sync through some kind of phase matching circuit. Adjusting that for tri-mode would be as simple as having a microcontroller read the frequency on the input and switch in he proper crystal. What I can seem to find information on is how the actual deflection circuits are designed. I'm assuming they are tuned for the frequency they should be scanning at but I'm not sure what kind of math I need to determine what components are needed.
Any information on CRT electronics design or the deflection circuits themselves would be greatly appreciated. Main reason I want to do this is that I have the means to and the cheapest I can get each screen working for arcade use is $100 per screen and only for a 15khz scanning rate
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tse
Joined: 03 May 2006
Posts: 1014
Location: Sweatbucket, Fl.
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| Posted: Sun Jul 24, 2011 12:03 am Post subject: |
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What frequencys are you wanting to scan? Is it like 640 x 480p or something higher? What is tri-mode?
Scott
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"Were we directed from Washington when to sow and when to reap, we would soon want bread."
Thomas Jefferson
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trebortaergeht
Joined: 14 Apr 2010
Posts: 73
Location: California
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| Posted: Sun Jul 24, 2011 12:54 am Post subject: |
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Tri mode refers to arcade monitors that can scan at all common arcade frequencies:(rounded) 15khz, 25khz, and 31khz. Basically cga, ega and vga
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CasetheCorvetteman
Joined: 09 Nov 2008
Posts: 6326
Location: Australia
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| Posted: Sun Jul 24, 2011 2:15 am Post subject: |
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So there isnt even an RGB where the on screen display goes out of its area?
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trebortaergeht
Joined: 14 Apr 2010
Posts: 73
Location: California
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| Posted: Sun Jul 24, 2011 2:28 am Post subject: |
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The display I have already modified had an osd rgb section but most american market tv's that were made in America(such as all the ones I have) have no rgb in the entire set, any international market sets will usually have rgb somewhere in the set such as the sanyo I have already modified
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CasetheCorvetteman
Joined: 09 Nov 2008
Posts: 6326
Location: Australia
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| Posted: Sun Jul 24, 2011 3:34 am Post subject: |
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Thats unfortunate. What about component? Do they have that? If so, use a NeoBits encoder, thatll do the job, they also have one that does S-video if you need that.
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trebortaergeht
Joined: 14 Apr 2010
Posts: 73
Location: California
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| Posted: Sun Jul 24, 2011 4:03 am Post subject: |
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The tv's that do have component almost always have rgb internals so a transcoder isn't needed. My main reasoning for wanting to do this is that I have a ton of 25" and larger crts that are in great condition but can't use them unless I either spend $100 per tube or modify the electronics to suit my needs.
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CasetheCorvetteman
Joined: 09 Nov 2008
Posts: 6326
Location: Australia
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| Posted: Sun Jul 24, 2011 6:47 am Post subject: |
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Use them on s-video or even compost video. Either that or they go to waste!!
All ya need is a few CXA1645 chips, which wont be dear.
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AnalogRocks
Forum Moderator
Joined: 08 Mar 2006
Posts: 26706
Location: Toronto, Ontario, Canada
TV/Projector: Sony 1252Q, AMPRO 4000G
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| Posted: Sun Jul 24, 2011 6:58 am Post subject: |
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| CasetheCorvetteman wrote: | Use them on s-video or even compost video. Either that or they go to waste!!
All ya need is a few CXA1645 chips, which wont be dear. |
Always recycle
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CRT.
HD done right!
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tse
Joined: 03 May 2006
Posts: 1014
Location: Sweatbucket, Fl.
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| Posted: Sun Jul 24, 2011 3:40 pm Post subject: |
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If I understand correctly the goal is to convert 15kHz CRT displays to run at 31kHz? The biggest dificulty will be modifying the horizontal deflection output stage. Because 31kHz is essentially half the time of 15kHz it will take twice the voltage that is applied to the deflection yoke to get the beam to sweep full screen. Once the beam has deflected from one side to the other it has to get back to the start side. Because the retrace time is short (about 25%) of the total line time the voltage required is very high. With 15kHz it might be 1000V or more. With the shorter time needed at 31kHz the switch will have to handle alot more, maybe 2000V. Alot of redesign will have go into that.
There used to be video scalers that could convert VGA to NTSC. Something like that might be alot easier to deal with.
Scott
_________________
"Were we directed from Washington when to sow and when to reap, we would soon want bread."
Thomas Jefferson
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Sun Jul 24, 2011 4:59 pm Post subject: |
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Whats your screen size or sizes your trying to display?
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trebortaergeht
Joined: 14 Apr 2010
Posts: 73
Location: California
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| Posted: Sun Jul 24, 2011 9:02 pm Post subject: |
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| macgyver655 wrote: | | Whats your screen size or sizes your trying to display? |
The screen sizes I am working with are 25", 27", and a couple of 30-34 tv's(these are the most common arcade screen sizes from the late 80' and on). If you meant resolution, then I want to design a board that can handle from 480i-480p and the resolutions in between.
| tse wrote: | If I understand correctly the goal is to convert 15kHz CRT displays to run at 31kHz? The biggest dificulty will be modifying the horizontal deflection output stage. Because 31kHz is essentially half the time of 15kHz it will take twice the voltage that is applied to the deflection yoke to get the beam to sweep full screen. Once the beam has deflected from one side to the other it has to get back to the start side. Because the retrace time is short (about 25%) of the total line time the voltage required is very high. With 15kHz it might be 1000V or more. With the shorter time needed at 31kHz the switch will have to handle alot more, maybe 2000V. Alot of redesign will have go into that.
There used to be video scalers that could convert VGA to NTSC. Something like that might be alot easier to deal with.
Scott |
Thank for the insight on the horizontal deflection issue. I've since found several design documents and aplication notes detailing horizontal deflection design, but these were all for tv's and made no note on input frequencies or ranges.
Where I am at now is trying to determine how deflection design is modified depending on the input frequency and how it can work with multiple frequencys. I know that the marquee can do 15khz to 130khz and that it uses a low and high range deflection circuit to do this but besides that, I don't know how it acomplishes the multiple frequencys in those ranges.
As for the actuall electronics design portion I've done similar things before. Those design documents seem very similar to the solid state tesla coil I built a few years ago.
| CasetheCorvetteman wrote: | Use them on s-video or even compost video. Either that or they go to waste!!
All ya need is a few CXA1645 chips, which wont be dear. |
They won't go to waste, I will at least get them working with 15khz rgb, wont bother with composite(lol compost) I hate it, and s-video isn't good enough, doesn't have that clean arcade look to it.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Sun Jul 24, 2011 9:18 pm Post subject: |
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Why not just pickup some CRT computer monitors in the sizes you need. 27, 32 and 36 inch monitors are still floating around and they already scan to at least 48khz, usually. Just have to adapt your game board output to the monitors input.
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trebortaergeht
Joined: 14 Apr 2010
Posts: 73
Location: California
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| Posted: Sun Jul 24, 2011 9:28 pm Post subject: |
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| macgyver655 wrote: | | Why not just pickup some CRT computer monitors in the sizes you need. 27, 32 and 36 inch monitors are still floating around and they already scan to at least 48khz, usually. Just have to adapt your game board output to the monitors input. |
That would be an option for newer games with VGA or higher, but won't work with the cga/480i(but I can mod a standard tv for these)or ega/320p games and I don't think I've ever seen a CRT computer monitor larger than 24".
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tse
Joined: 03 May 2006
Posts: 1014
Location: Sweatbucket, Fl.
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| Posted: Sun Jul 24, 2011 11:53 pm Post subject: |
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| trebortaergeht wrote: |
Thank for the insight on the horizontal deflection issue. I've since found several design documents and aplication notes detailing horizontal deflection design, but these were all for tv's and made no note on input frequencies or ranges.
Where I am at now is trying to determine how deflection design is modified depending on the input frequency and how it can work with multiple frequencys. I know that the marquee can do 15khz to 130khz and that it uses a low and high range deflection circuit to do this but besides that, I don't know how it acomplishes the multiple frequencys in those ranges.
As for the actuall electronics design portion I've done similar things before. Those design documents seem very similar to the solid state tesla coil I built a few years ago.
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When a multi freq scan system is designed one starts at the highest frequency and selects a deflection yoke that will do what is wanted with reasonable voltages. The voltages just decrease with lower freqs. Other things like linearity problems start to show up if going low enough. That is why the Marquee starts with the two horizontal windings (in each yoke) in parallel at the higher frequencies and connects them in series for the lower freqs.
If you can find monitor yokes that will fit the neck size of the CRTs that you want to mod it might be feasable to come up with something to scan higher freqs.
Scott
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"Were we directed from Washington when to sow and when to reap, we would soon want bread."
Thomas Jefferson
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Mon Jul 25, 2011 12:25 am Post subject: |
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| trebortaergeht wrote: | | I don't think I've ever seen a CRT computer monitor larger than 24". |
I've owned and repaired 27", 32" and 36" crt monitors.
Not sure how well the focus grid of a 480i tube would handle higher beam current. It was never designed for that volume of electrons. For that matter, not sure if the gun assy is capable of producing the volume of electrons required for higher scan rates.
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CasetheCorvetteman
Joined: 09 Nov 2008
Posts: 6326
Location: Australia
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| Posted: Mon Jul 25, 2011 7:28 am Post subject: |
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If its a 15kHz arcade machine, it will be VERY UNLIKELY that it will be 480i. Ive got a few here, and not a single one is 480i. The output is almost always 240p, or somewhere close to that. Almost all the ones ive worked on or owned have put out progressive scan images.
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trebortaergeht
Joined: 14 Apr 2010
Posts: 73
Location: California
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| Posted: Mon Jul 25, 2011 8:26 am Post subject: |
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| CasetheCorvetteman wrote: | | If its a 15kHz arcade machine, it will be VERY UNLIKELY that it will be 480i. Ive got a few here, and not a single one is 480i. The output is almost always 240p, or somewhere close to that. Almost all the ones ive worked on or owned have put out progressive scan images. |
I did specify both cga(240p) and 480i which have the same scan requirements and will work on a standard tv as long as you can get it to work with rgb, I've already got a second tv working with rgb at 240p.
| macgyver655 wrote: | I've owned and repaired 27", 32" and 36" crt monitors.
Not sure how well the focus grid of a 480i tube would handle higher beam current. It was never designed for that volume of electrons. For that matter, not sure if the gun assy is capable of producing the volume of electrons required for higher scan rates. |
I"ll keep an eye on craigslist incase any pop up. I've found several commercially made arcade monitor chassis that sync to all three frequencies and they claim it works with most crts as long as they arent too old and you match the impedance of the deflection yoke to the circuit.
| tse wrote: | When a multi freq scan system is designed one starts at the highest frequency and selects a deflection yoke that will do what is wanted with reasonable voltages. The voltages just decrease with lower freqs. Other things like linearity problems start to show up if going low enough. That is why the Marquee starts with the two horizontal windings (in each yoke) in parallel at the higher frequencies and connects them in series for the lower freqs.
If you can find monitor yokes that will fit the neck size of the CRTs that you want to mod it might be feasable to come up with something to scan higher freqs.
Scott |
Thanks for the info, I've got about 3 pallets of computer monitors to experiment with(none suitable as is because the largest ones I have are 21" and none will scan below 30khz). I'll also try a few of the tv's I have and see if I can get them to work with higher frequencies
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CasetheCorvetteman
Joined: 09 Nov 2008
Posts: 6326
Location: Australia
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| Posted: Mon Jul 25, 2011 9:09 am Post subject: |
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Yes i know you did, but in order to be sure everyone else knows that is a requirement, i posted it.
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macgyver655
Joined: 22 Aug 2007
Posts: 8508
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| Posted: Mon Jul 25, 2011 1:47 pm Post subject: |
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| trebortaergeht wrote: |
I'll also try a few of the tv's I have and see if I can get them to work with higher frequencies |
Another thing you have to remember is that a standard tv picture tube has a shadow mask (except Sony) which would limit the display resolution cause the mask has limited pixels as to what it was designed for(480i). It may still produce a picture at a higher resolution but would probably loose clarity at higher rates if the beam was slightly missing it's color phosphor spot.
A pc monitor uses an aperture grill (a few use a shadow mask) that is designed with more available pixels spots.
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