Caution when using an Emotia + Scanline Generator

[matrigs]

I would like to address some concerns that i have when using an Extron Emotia together with a Scanline Generator based on the 74HC74 and 74HC125 chips. So this includes all DIY Scanline Generators as well as Toodles and the Mini-SLG.

I tried to make a setup for comparing the picture quality between a Naomi Universal screen and a CRT TV. I used a Xbox 360 set to 640x480, connected it to an Extron Emotia, connected the BNC outputs to my CRT TV and the VGA through to my Naomi. I then proceeded with connecting my self built Scanline Generator in between the Naomi and the Extron Emotia.

Suddenly something happened with the output on my CRT TV, which got significantly darker. I disconnected the Scanline Generator and the picture went back to normal, but i realised that my XBOX 360 has crashed. Sadly, it doesn't boot up anymore and it looks like this small experiment burned some mosfets on the output stage of the console.

Something similar happens when i connect my PC to the whole setup, the CRT screen darkens but my graphics card doesn't crap out. I would assume it has much more sophisticated safety measures which doesn't allow the voltage to travel back.

It has been addressed several times in various topics that it is unclear if those scanline generators can do any harm to your hardware. Keep in mind that the construction based on the 74HC74 and 74HC125 chips simply grounds the RGB lines of the VGA output without any additional protection, which is against any common sense for anyone having some basic electronic knowledge.

I don't want to start some panic, as this is a very specific setup, contains DIY stuff and was done without any safety precautions, yet i would like to point out that his has happened to me.

Also, due to what i mentioned earlier, this setup doesn't even do what it is supposed to (maybe someone can shed some light, why the Extron darkens out the CRT picture) so it isn't necessary for anyone to redo it.

[fagin]

I'm confused slightly...... isn't the Emotia being used as a scan convertor and if so, why would you want to be connecting out to a CRT TV and a 31khz device?

[Crafty+Mech]

It has been addressed several times in various topics that it is unclear if those scanline generators can do any harm to your hardware. Keep in mind that the construction based on the 74HC74 and 74HC125 chips simply grounds the RGB lines of the VGA output without any additional protection, which is against any common sense for anyone having some basic electronic knowledge.

The mini SLG does not use the 74HC125, it is a single-chip design, and has nothing to do with your DIY device.

You connected a "self-built" SLG to your equipment and damaged your hardware. My bet is there is a short in your SLG wiring, and when connected in the manner you described with your equipment, poof went your Xbox.

I've sold 240 mini SLG units, and I've never had a case of an SLG damaging anyone's equipment.

I'm also confused that if "grounding" the RGB lines with a 74HC125 is "against any common sense", why did you build your SLG that way?

[matrigs]

The mini SLG does not use the 74HC125, it is a single-chip design, and has nothing to do with your DIY device.

I have to apologise for mentioning your device, then. I was convinced that it uses the same chips. I didn't mention the SLG3000 as i know it has a totally different approach. In fact, if you allow i will order one from you asap.

You connected a "self-built" SLG to your equipment and damaged your hardware. My bet is there is a short in your SLG wiring, and when connected in the manner you described with your equipment, poof went your Xbox.

Yes that is certainly true. The sad part is that i never had any other issues with my homebuilt boxes apart from this certain setup, and it poofed immediately.

I've sold 240 mini SLG units, and I've never had a case of an SLG damaging anyone's equipment.

Actually, i have never heard of any damage with any commercial scanline generator.

I'm also confused that if "grounding" the RGB lines with a 74HC125 is "against any common sense", why did you build your SLG that way?

I didn't invent the wiring. It was posted several months ago here: http://www.mmmonkey.co.uk/console/other ... nlines.htm
I know that Toodles generator uses the same scheme, and as i mentioned before was convinced yours too.

As to the "against common sense" phrase: I used it because whatever the odds, it worked (also in commercial products, see above). And it worked pretty darn good. I think a few guys
on this board and several others built them too without any problems whatsoever, so i gave it a go.

Either way i will go for your product.

I'm confused slightly...... isn't the Emotia being used as a scan convertor and if so, why would you want to be connecting out to a CRT TV and a 31khz device?

The "Monitor" port on the Extron passes through the VGA input unaltered, so still 31 khz. So i connected my Naomi screen to this one. The idea was to compare the two outputs at once.

Lesson learned. I actually just got my Xbox back from repair two weeks ago after a reball and a broken HANA chip.

[Fudoh]

Moosmann onced warned me about this and pointed to the design on the mmmonkey page, but this was a long time ago, around the time when the SLG3000 was introduced.

[matrigs]

Moosmann onced warned me about this and pointed to the design on the mmmonkey page, but this was a long time ago, around the time when the SLG3000 was introduced.

Well the design was inspired by the SLG3000 and invented by some korean guy:

http://sharksym.egloos.com/4930096

So the mmmonkey scheme comes from there.

As i mentioned it is generally considered to be bad design when a device connects anything directly to ground.

I have to admit again, that when i look at Toodles or Brunofreitas RetroVga, i can in fact see some additional diodes, which may make the device safer.

[Crafty+Mech]

RGB signal lines are terminated at the source end typically by 75 ohm resistors, so there is some implicit short protection. To short proof the 74125 design, placing a current limiting resistor (say 100ohms) in series with the grounded inputs of the 125 would do the trick. Depending on the value used the scanlines would not be straight black, but generally that doesn't seem to be desirable anyway.

If your interested in the mini, send me a PM about the setup you would like to use it with. I recommend that the mini is placed at the very end of the video chain, connected directly on one end to the monitor.

[matrigs]

send me a PM about the setup you would like to use it with.

Right - i read your site today and saw that you are selling two different versions, one for mame one for arcade games. Could you elaborate a little on what the difference is between the two?

[Crafty+Mech]

The "PC" version has a slight design tweak that solved a compatibility problem with NVidia and Radeon video cards.

I'm actually just about out of boards, so I've taken the opportunity to upgrade the design to be universal for both MAME/PC, console, and arcade hardware. So I've actually been telling everyone that I would wait a couple weeks to order until I release version 2. That way if you ever want to throw it on a PC setup, you don't have to order a second unit.