BenQ BL702A Problem - YUV/RGB mode

[dingsbums]

So I finally bought a BenQ BL702A LCD. It has a 5:4 aspect ratio and is multisync (15/24/31 khz) and has nearly zero input lag = perfect for me .
I bought it to connect my retro consoles with RGB.
It is really a great screen (especially for the price) and I'm happy with it except for one thing => see more below.
The screen only has one VGA Input so I connect my consoles with the Sync Strike http://arcadeforge.net/Scaler-and-Strik ... ::15.html​
All the Sync Strike does is adapting Scart RGB to RGBHV as VGA Pinout - so no external scaling .


The BenQ BL702A registers the input through the colour palette as RGB or YUV input and here is where my problem begins .


On the MD1/2 and the PS1/2 the Benq BL702A starts in the YUV mode (although the consoles are connected through RGB) and it results in a redish picture . I can switch them manually in the BenQ BL702A menu to RGB but as soon as a level on a game ends and the screen goes black for a split second it switches back to YUV .

My questions are (info is very hard to find on this): Is the RGB and YUV signal both transmitted through Scart ? Why is the screen switching to YUV when it is a RGB signal ? How does the screen decipher if it switches to RGB or YUV ? And why is this only on the MD 1/2 and the PS1/2 the case ? (the consoles give a RGB picture on all other screens with the same cables) - is the RGB signal on these two consoles different ? I really doubt that.
Could this be a case of 75Ohm and TTL Level signals ?


The pictures to all of this:

MD1/2 (screen starts at YUV although connected through RGB)

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MD 1/2 (manually switched to RGB - this is how it should be from the start)

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PS1/2 (screen starts at YUV although connected through RGB)

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PS1/2 (manually switched to RGB - this is how it should be from the start)


As example two consoles where it works without a problem (PCE & SAT)



And what confuse me the most Mega Drive 1 (screen starts in YUV mode) and Master System 1 using the same AV pinout and RGB cable => I would have bet everything that the screen with the Master System 1 would also start in the YUV mode but to my surprise the screen starts in the RGB mode => complete confusion .

​
If anybody knows something (VGA Pin that does the switching between RGB and YUV mode maybe ???) please help. Googling about this issue didnt help at all.

[Guspaz]

VGA does not support YPbPr, so there's no pin for indicating that (meaning using YPbPr over VGA is a non-standard extension that some devices do). Since YPbPr and RGB are electrically identical, I'm not sure how the monitor could detect which it's being fed, unless maybe it uses the presence of sync on Green/Luma to indicate YPbPr? The PS2's RGB output is RGsB (at least in North America), but the Megadrive and PS1 aren't, to my knowledge...

Maybe try changing the DDC/CI setting in the SYSTEM menu to the opposite of whatever it is now. That may change the auto-detect behaviour.

If the problem somehow is RGsB signals, I don't think the Sync Strike can convert RGsB into RGBS (at least there is no mention of it), it seems to be about converting RGBS into RGBSV while stripping composite video from the csync. As such, I think that if you feed an RGsB signal to a sync strike, you would get RGsB out, and maybe your monitor is seeing sync on green and thinking it is probably component with sync on luma? I'm speculating, really, no idea.

[Fudoh]

The PS2's RGB output is RGsB (at least in North America)

only for 480p. For 15khz (240p and 480i) it's RGBs.

[Xyga]

If preventing the automatic detection with a resistor could work you'd have to find on which pin and what impedence indeed (do we know the threshold anyway?)

I've experienced a similar problem with the DVDO VP30, when feeding an XRGB-2 to the RGBHV input, it would occasionally start as YUV.
Powering the DVDO after the XRGB somewhat helped but not always: you could try that (I mean turning the monitor on last) if it works at least it will be less bothersome than going through the menus every time to switch manually.
(of course that's not a viable solution when you're in the middle of playing a game >>)

[dingsbums]

VGA does not support YPbPr, so there's no pin for indicating that (meaning using YPbPr over VGA is a non-standard extension that some devices do). Since YPbPr and RGB are electrically identical, I'm not sure how the monitor could detect which it's being fed, unless maybe it uses the presence of sync on Green/Luma to indicate YPbPr? The PS2's RGB output is RGsB (at least in North America), but the Megadrive and PS1 aren't, to my knowledge...

Maybe try changing the DDC/CI setting in the SYSTEM menu to the opposite of whatever it is now. That may change the auto-detect behaviour.

If the problem somehow is RGsB signals, I don't think the Sync Strike can convert RGsB into RGBS (at least there is no mention of it), it seems to be about converting RGBS into RGBSV while stripping composite video from the csync. As such, I think that if you feed an RGsB signal to a sync strike, you would get RGsB out, and maybe your monitor is seeing sync on green and thinking it is probably component with sync on luma? I'm speculating, really, no idea.

Thanks for your answer / suggestions.
I have wired all my consoles RGB cables using composite as sync since the Sync Strike is stripping it anyway. So there's no pssibility it has to do with sync on green / sync on luma.
There is going RGBS in the Sync Strike and it does output RGBHV.
Just for shits & giggles I wired up the secondary output with the screw terminals on the sync strike. There I tried sync on green (to see if it fixes the issue) but it turns out the BenQ BL702A accepts sync on green without any problem but the screen behaves exactly the same with sync on green => the MD1/2 & PS1/2 start in the (redish) YUV mode.

I just tried changing the DDC/CI setting (it was on, changed it to off) but that didn't change anything sadly .

[Guspaz]

The PS2's RGB output is RGsB (at least in North America)

only for 480p. For 15khz (240p and 480i) it's RGBs.

In which case, if everything is being fed to the monitor as RGBSV, all that's left that the monitor could try to use to determine that automatically is 15khz vs 31khz... I'm not sure it's actually possible to tell RGB and YPbPr apart...

[dingsbums]

If preventing the automatic detection with a resistor could work you'd have to find on which pin and what impedence indeed (do we know the threshold anyway?)

I've experienced a similar problem with the DVDO VP30, when feeding an XRGB-2 to the RGBHV input, it would occasionally start as YUV.
Powering the DVDO after the XRGB somewhat helped but not always: you could try that (I mean turning the monitor on last) if it works at least it will be less bothersome than going through the menus every time to switch manually.
(of course that's not a viable solution when you're in the middle of playing a game >>)

I already tried powering the monitor last => didn't help
Which pin would you suggest putting a resistor - the RGB lines or the sync lines ? Or all of them ?

The PS2's RGB output is RGsB (at least in North America)

only for 480p. For 15khz (240p and 480i) it's RGBs.

In which case, if everything is being fed to the monitor as RGBSV, all that's left that the monitor could try to use to determine that automatically is 15khz vs 31khz... I'm not sure it's actually possible to tell RGB and YPbPr apart...

Actually all I'm feding the monitor at the moment are 15khz RGB consoles (PS1/2, MD1/2, SFC, SAT, FC, PCE, N64, MS1).

[Guspaz]

Every one of those would have slightly different timing, though, so it's possible that some of them trigger the monitor's logic and others don't.

[Ikaruga11]

So I finally bought a BenQ BL702A LCD. It has a 5:4 aspect ratio and is multisync (15/24/31 khz) and has nearly zero input lag = perfect for me

How can an LCD be multi-sync? They're fixed pixel displays, and thus have one native resolution.

[Xyga]

How can an LCD be multi-sync? They're fixed pixel displays, and thus have one native resolution.

It's not exactly 'multisync' but rather 'not giving a damn about sync' if the theory's right.
That's what you'd commonly find on old non-widescreen pre-HD flat panel displays, as some suggest fixed matrix displays wouldn't need the sync info to work so they only take the portion of the signal they need and render frames with only the pixel upscaling done.
I don't know how it's supposed to work exactly but it was the standard behaviour before the industry got in line with the modern digital broadcast and video standards, where built-in I/O-scalers boards only manage a defined, limited array of resolutions and refreshes.
This is also what makes people think G-Sync and FreeSync are more or less marketing bullshit...

[dingsbums]

It does work with 15/24/31 khz signals => I'm calling it multisync That's probably the wrong term but I don't care .
PS: This LCD is not old => it's from 2014/15 and you can buy it new from Amazon .

PPS: Yesterday I measured the voltage signals from the RGB & Sync lines from the consoles the screen does work with, then MD1/2 & PS 1/2. I came to conclusion that you have to remove the caps (PS 1/2) / the resistors (MD 1/2) => that did change the voltage levels on the RGB lines but sadly the problem didn't change at all .

I'm out of ideas .

[Xyga]

The product doesn't have to be old, it's the built-in electronics design that is (same as early lcd monitors).
Several manufacturers seem to have kept it for that particular segment/category (5:4) which again would probably be wrong to call multi-sync, but rather free-sync (yes!) or sync-free or even broad-sync...anyway whatever it's called is not really important.

What's too bad is that this aging tech actually fits our retrogaming needs better, but there's no way manufacturers would go back and include it to the broader consumer mass market (current widescreen monitors and tvs).
Although I still suspect this is almost exactly what AMD's FreeSync actually is.