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How to use SCART for our hobby

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Level42:
Geeez.....was working on my Centipede the other day and suddenly realised that I hadn't included the resistors in the RGB lines when you use the schematics.

The thing is, that real Arcade PCBs deliver a TTL level video signal. This can be 5Vtt. A VGA card, will only supply 1V.  Following this, you can use the schematics like indicated with a PC (VGA) connection.

However, if you want to connect a real arcade PCB (OR f.i. a J-Pac) you will need to add a resistor in series with each color signal. I've found 150 Ohms to be a good value.

I will try to re-write everything to make it clear what to do for PC versus arcade PCB situations....but I'm limited in time this week....

Zebidee:
I've done countless VGA-SCART conversions for TVs. 

This includes a couple of JAMMA-SCART setups for arcade cabs, to allow you to take the PC/JPAC out and plug a JAMMA PCB in. The monitors I used were Sony professional video monitors ("broadcast" monitors, used in TV studios).  If you want to do this, you will need to use resistors on the RGB signals (but not the sync).

I tested a few different resistor values, and found that 75ohms seemed to work the best in this instance.  100ohm resistors work fine as well, but the colours were slightly duller (but acceptable).  75ohm resistors gave superior results.  The clients that ended up with these systems were both very happy.

For comparison, I also had another cab running with one of these Sony monitors, but with a straight VGA-SCART cable.

I tested these JAMMA-SCART systems using video output from a JPAC, which boosts the video signals to levels appropriate for an arcade monitor.  In fact, the RGB signals were normally around 1.2-2v from the JPAC (not 5v), but under 1v after applying resistors.

Sync signals from the JPAC came through at about 3.3-3.5v, and there was no need to put a resistor on this signal line (I tried, but it gave inferior results, such as poor sync at the top of the screen).  Note that actual arcade PCB voltages may vary somewhat.

Regarding the 5v input to pin 16 for RGB-AV switching - TVs vary with their need for this.  Mostly, I've done it by just running a short wire from pin 20 (ie sync) to pin 16, and this has worked fine.  I'd recommend to people that they try this method first, because it is much simpler.  However, some TVs are a bit fussier, and I've had to run a separate 5v signal with a resistor on it (much as you've shown in your diagram).  The reason (I believe) is that the sync signal voltage will actually vary a bit, and this variation is unacceptable for certain TVs.  The brands I've needed to do this with tended to be TEAC TVs in particular, although you may find that other individual TVs of any brand may require this.  However, I've never encountered the need to run a separate 5v signal to pin 16 for any LOEWE, SONY or PHILLIPS SCART TVs.  It seems that the better quality TVs are more forgiving.

Regarding the need for a 12v signal to pin 8, there is no consistency here.  I once had a Phillips 29" TV, dead from the dump with failed tuner, but it worked fine as an arcade monitor once I hooked up a cable with a 12v switching signal.  once again, TEAC TVs tend to require this 12v switching signal.  As you can probably guess, I try to avoid TEAC TVs nowadays.  They are a poorer-quality brand anyway.

I apologise for the long post.  I should probably write this up somewhere in a more structured way ....

Zeb.

Level42:
I tried to stick to the standards as they were defined. This because it will work for everyone. I know some TV's accept 5V instead of 3,5 V. But because I wasn't aware of it, I lost a couple of hours on finding out why my next TV I worked on (Which was newer) DIDN"T work....

So, stick to the standards, and you'll be 100% sure it works.
 

Constructacon:
Hi I'm new here and trying to build my first MAME cabinet.

I'm in Australia and fluked getting a TV with a SCART connector. After reading this I consider myself very lucky. I'm trying to make a VGA-SCART cable but am wondering about the SCART pin 21. Where does it get wired to? It says ground so is jumping it accross to pin 18 (0v) an acceptable alternative?

Level42:
Pin 21 is simply the outer shield of the cable and connector. It's the metal edge of the connector.
The purpose is to shield of any signals from outside the cable to interfere.

So far, I haven't bothered to connect it. (Classic) arcade video signals were low-res and cab builders didn't do any shielding of the wires etc. So there's no real need to do it now.

Since you're making VGA to SCART, you could connect the outer shield of the VGA cable to it. Won't harm.

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