"rolling screen" when starting a core : long-term harm for CRT ?

Discussion about displays and related hardware including MiSTer filters and video settings.
Airbag
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"rolling screen" when starting a core : long-term harm for CRT ?

Unread post by Airbag »

Hello,

I'm using mainly a CRT TV with my MiSTer and I usually get a "rolling screen" for a few seconds each time I start a new core. (For example : if it's the Neogeo core, the screen shows at this moment "Kbd mode : Joystick 1")
I would like to understand what happens at this time, what triggers this effect.
I guess my CRT receives a signal that it's not supposed to have, maybe 31 kHz instead of 15 khz. (Assumption 1)

I read sometimes that unsuitable signal can damage the CRT.
You may say it's only for a few seconds. But what if I use the (excellent) Super Attract Mode ? Every 2min I will get again the unsuitable signal on the CRT.
Am I slowly but surely damaging it ? (Assumption 2)
Should I avoid Super Attract Mode for this reason ?

If a MiSTer dev could confirm/explain 'Assumption 1', I would be very happy :)
Thanks

Edit : for the record my (fairly standard ?) MiSTer.ini : https://pastebin.com/jNZusKXS

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Re: "rolling screen" when starting a core : long-term harm for CRT ?

Unread post by LamerDeluxe »

I use SAM as well on my CRT monitor and I think it is just a temporary loss of sync, while cores are switching. I don't expect this to be harmful.

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Re: "rolling screen" when starting a core : long-term harm for CRT ?

Unread post by Airbag »

Can you explain what you mean with "loss of sync" ? I think there is a signal coming (since I can read "Kbd mode : Joystick 1" while the rolling effect is effective)
My question is : what are the properties of this signal ? (see "assumption 1" in 1st post)

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Re: "rolling screen" when starting a core : long-term harm for CRT ?

Unread post by retrodroid »

The CRT is an analog device, so it has an imperfect mechanism for locking the incoming signal, which can result in the "rolling screen" effect you are seeing. This won't hurt your monitor, so long as the incoming frequency is within spec for the monitor. You may be able to adjust your monitor to lock in to the frequency faster, though sometimes you need different monitor adjustments for slightly different frequencies, which can be tedious because a "perfect" config for one game will cause another to continue to roll the screen forever.

If you are using a low res. arcade monitor, then you'll want to ensure your cores are all outputting around 15Khz freq., and certainly not 31Khz, but if that were the case it wouldn't result in a few seconds of rolling and then a proper lock, things would be very messed up.

I'm not familiar with SAM, but perhaps there is a way to configure it to only run cores that output frequencies that your CRT can handle.

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Re: "rolling screen" when starting a core : long-term harm for CRT ?

Unread post by Airbag »

Thanks for your feedback. Still, it does not explain whats happens.
My MiSTer "core menu" outputs 15 kHz, the cores I use also all outputs 15 kHz. (I don't use ao486 on this CRT TV)
So why the rolling effect for a few seconds ?
=> It's not like going from 240p to 480i : this change happens in less than 1 second, without rolling effect. (example : boot sequence on playstation core)
=> it does not look either like a loss of signal (because something is displayed)

Moreover, another interesting test :
=> if I plug to my CRT a SNES, a Genesis, and a PC (which outputs a suitable signal) and switch (with a SCART switch) "on the fly" between these 3 inputs (+ MiSTer FPGA input) : I don't have a rolling effect.

Still hoping that a MiSTer dev could answer and debunk all our user assumptions :)

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Re: "rolling screen" when starting a core : long-term harm for CRT ?

Unread post by FoxbatStargazer »

15khz is the horizontal refresh, the vertical refresh can vary. Most NTSC consoles are around 59.97 but not exactly, with the SNES being slightly above and the Genesis being slightly below, for example. Arcade cores can deviate more and anything PAL will be down to 50.

The Mister is also going to drop signal at least very briefly when you switch a core, it needs time to flash the core before getting the video running, even if you can't tell easily with the rolling going on. So its not like switching signals between three consoles that are kept on.

240p is like a trick/extension of 480i, an analogue TV effectively won't even notice a difference, its the same format.

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Re: "rolling screen" when starting a core : long-term harm for CRT ?

Unread post by Airbag »

New interesting theories, let's see that.

FoxbatStargazer wrote: Tue Feb 13, 2024 4:05 am

15khz is the horizontal refresh, the vertical refresh can vary. Most NTSC consoles are around 59.97 but not exactly, with the SNES being slightly above and the Genesis being slightly below, for example. Arcade cores can deviate more and anything PAL will be down to 50.

I use my SNES and Genesis both with PAL refresh rate and NTSC refresh rate (yes they are "tweaked", I can switch "on the fly" by long-pressing the "reset" button). Never had rolling effect when switching 50 Hz <=> 60 Hz, it's instant.
So let's rule out vertical refresh change : my CRT syncs very quickly when it's modified.

FoxbatStargazer wrote: Tue Feb 13, 2024 4:05 am

240p is like a trick/extension of 480i, an analogue TV effectively won't even notice a difference, its the same format.

Not exactly the same format, some scalers do have problems with that kind of 240p <=> 480i switch but that's not my point of interest for this thread. (And I don't use scalers in this setup).

FoxbatStargazer wrote: Tue Feb 13, 2024 4:05 am

The Mister is also going to drop signal at least very briefly when you switch a core, it needs time to flash the core before getting the video running, even if you can't tell easily with the rolling going on. So its not like switching signals between three consoles that are kept on.

I'm not sure it's about the time to load the core, it feels it's almost instant. (see second point below)
To summarize :

  • before the rolling effect, I have 15kHz "CRT TV compliant" signal, after the rolling effect, I have 15 kHz "CRT TV compliant" signal
  • during the rolling effect (about 2 seconds), a core is already loaded and the signal is not dropped (because I see the message "Kbd mode..." on the screen. But I can't tell if it's from the "targeted" core or MiSTer main menu core !)

So the question remains : what is happening exactly with this video signal during the rolling effect, before the console/arcade/computer core menu is displayed ?

As the MiSTer "main menu" core's behavior could be something to investigate, maybe I should ask the question directly on Sorgelig's patreon. But I'm afraid of being swiftly dismissed :D

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Re: "rolling screen" when starting a core : long-term harm for CRT ?

Unread post by FoxbatStargazer »

I'm not saying the signal is down for 2 seconds. But that the period it is down (and it has to be down for at least a bit) might cause the TV sync to go weird and it takes 2 seconds to recover. Not that anything is necessarily wrong with the video signal during this period (although it might be), but rather that your TV gets in some state during the dropped signal that takes a bit to recover from once a decent signal is sent.

Your connection type might play into this. In general Mister has been very solid for me with RGBHV. With component people have had issues with dropped sync in certain scenes on some TVs. And the composite/s-video support is somewhat fresh so there may be additional issues.

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Re: "rolling screen" when starting a core : long-term harm for CRT ?

Unread post by retrodroid »

This won't damage your CRT. You could try playing with your vertical hold adjustment on your CRT to see if you can improve things (or make them worse). :)

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Re: "rolling screen" when starting a core : long-term harm for CRT ?

Unread post by Airbag »

retrodroid wrote: Thu Feb 15, 2024 4:59 pm

This won't damage your CRT. You could try playing with your vertical hold adjustment on your CRT to see if you can improve things (or make them worse). :)

I respect your opinion, but what is your justification ? How can you justify that without knowing the signal output ?

FoxbatStargazer wrote: Thu Feb 15, 2024 2:17 pm

I'm not saying the signal is down for 2 seconds. But that the period it is down (and it has to be down for at least a bit) might cause the TV sync to go weird and it takes 2 seconds to recover. Not that anything is necessarily wrong with the video signal during this period (although it might be), but rather that your TV gets in some state during the dropped signal that takes a bit to recover from once a decent signal is sent.

Your connection type might play into this. In general Mister has been very solid for me with RGBHV. With component people have had issues with dropped sync in certain scenes on some TVs. And the composite/s-video support is somewhat fresh so there may be additional issues.

I also use RGB : VGA to SCART cables, some with composite sync forced, some without (and composite_sync=1 in MiSTer.ini).

I suddenly realize that I should have begun with this very basic question : do you have the rolling effect when you load a core ? What do you see ?

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Re: "rolling screen" when starting a core : long-term harm for CRT ?

Unread post by retrodroid »

Airbag wrote: Thu Feb 15, 2024 6:51 pm
retrodroid wrote: Thu Feb 15, 2024 4:59 pm

This won't damage your CRT. You could try playing with your vertical hold adjustment on your CRT to see if you can improve things (or make them worse). :)

I respect your opinion, but what is your justification ? How can you justify that without knowing the signal output ?

40 years of experience? :D You wouldn't see a mostly formed image of the screen that happens to roll vertically a few times before settling in if the frequency was completely out of range. Like I said, you can play with the vertical hold adjustment on your monitor if you want and it might lock it in immediately instead of rolling a bit first.

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Re: "rolling screen" when starting a core : long-term harm for CRT ?

Unread post by Newsdee »

Airbag wrote: Wed Feb 14, 2024 12:45 am
  • during the rolling effect (about 2 seconds), a core is already loaded and the signal is not dropped (because I see the message "Kbd mode..." on the screen. But I can't tell if it's from the "targeted" core or MiSTer main menu core !)

If I understand you correctly, you are seeing a stable box with the OSD saying "'kbd mode... (etc)" but the rest of the video is rolling?

The HDMI and VGA porte on MiSTer are wired directly to the FPGA. Once you select a core in the main menu all video goes through the core.

So if you are seeing a stable message box (but with garbled background) that means the core is running 15khz video as expected. Its the "internal" core video that is having issues.

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Re: "rolling screen" when starting a core : long-term harm for CRT ?

Unread post by Newsdee »

Looking at your INI file, why is this commented out?

Code: Select all

;video_mode=0

Are you using an analog IO board (or equivalent), or are you using direct video? In the latter case you will need to check any settings that can affect the HDMI signal

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Re: "rolling screen" when starting a core : long-term harm for CRT ?

Unread post by Airbag »

Newsdee wrote: Fri Feb 16, 2024 5:19 am
Airbag wrote: Wed Feb 14, 2024 12:45 am
  • during the rolling effect (about 2 seconds), a core is already loaded and the signal is not dropped (because I see the message "Kbd mode..." on the screen. But I can't tell if it's from the "targeted" core or MiSTer main menu core !)

If I understand you correctly, you are seeing a stable box with the OSD saying "'kbd mode... (etc)" but the rest of the video is rolling?

The HDMI and VGA porte on MiSTer are wired directly to the FPGA. Once you select a core in the main menu all video goes through the core.

So if you are seeing a stable message box (but with garbled background) that means the core is running 15khz video as expected. Its the "internal" core video that is having issues.

No, the whole screen has the rolling the effect, including the part where I can read the msg box.
Do you use a CRT and do you have a rolling effect when you load a core ?

Newsdee wrote: Fri Feb 16, 2024 5:25 am

Looking at your INI file, why is this commented out?

Code: Select all

;video_mode=0

Are you using an analog IO board (or equivalent), or are you using direct video? In the latter case you will need to check any settings that can affect the HDMI signal

Can't use Direct Video with a VGA-to-SCART cable :)
It's an Analog IO board from Antonio Villena
Do you use a CRT and do you have a rolling effect when you load a core ?

By the way, guys, if you don't know what happens with the signal : please don't try to guess. (We already did)
=> I'm interested by answers of someone who knows and understand what the cores are really doing with the signal :)

Meanwhile, if you are not a core dev (but just a CRT user like me), I'm still very interested by what you see (I wrongly assumed that every CRT user had the rolling effect). Please state what you see and what you use :

  • rolling effect yes/no (if yes : when, for how long)
  • brand/model of the CRT
  • if you can : details about hardware used : Digital board (with direct video) + type of cable / Analog board + type of cable (manufacturer ?)

Thanks again for your contributions

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Re: "rolling screen" when starting a core : long-term harm for CRT ?

Unread post by annette »

Airbag wrote: Fri Feb 16, 2024 5:50 pm

It's an Analog IO board from Antonio Villena

Why do you not ask Antonio Villena if this is expected behaviour for his custom designed IO board?

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Re: "rolling screen" when starting a core : long-term harm for CRT ?

Unread post by paulbnl »

You are getting a rolling screen because your TV needs composite sync.

When a core starts it is outputting H/V sync by default until the MiSTer Main software tells the core to output composite sync which takes a short while.

This means your TV is not receiving a Vsync signal during that time so it will generate its own Vsync and this results in the rolling screen.

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Re: "rolling screen" when starting a core : long-term harm for CRT ?

Unread post by FoxbatStargazer »

paulbnl wrote: Fri Feb 16, 2024 7:09 pm

You are getting a rolling screen because your TV needs composite sync.

When a core starts it is outputting H/V sync by default until the MiSTer Main software tells the core to output composite sync which takes a short while.

This means your TV is not receiving a Vsync signal during that time so it will generate its own Vsync and this results in the rolling screen.

Interesting. I've never had to use composite sync, only HV, or else SoG, which is handled with a hardware switch. Might be why I've never seen the issue!

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Re: "rolling screen" when starting a core : long-term harm for CRT ?

Unread post by Newsdee »

I noticed this video had "rolling" effect when loadinfg a core from menu. Is that what you experienced?
https://youtu.be/r-chjXlvb8g?si=sCrT_z7SECfk_g5Z

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