Arcade PCB video output at 5Vpp ?

[Level42]

I've read that real arcade video cards put out 5Vpp RGB (and sync) signals, since most use TTL IC's, so there's a TTL level on those outputs.

Now, I've hooked up a TV to my Galaxian PCB and used 390 Ohms resistors in series on the RGB signals, since SCART RGB signal level is normaly 0,7Vpp. However, the picture is now quite dim. I can easily compare it to the on-screen menu's that are very bright and clear.

I think I calculated the resistor values right, so I wonder why the picture is so dim, obviously the values are too high. The SCART is giving a 75 Ohms resistor as impedance (so parallel to gnd) on the signal.

Anyone can help calculate the correct value ? I don't have an oscilloscope to measure this....

[Rickn]

Yes Original Arcade boards that run Standard (CGA) or Mid Res (24.3Kz) run TTL, that means 3 to 5 volts video and sync outputs, terminated at either 390 ohms or 1Kohm

Video Cards typicaly run ,7 volts video and 1 volt sync-this is standard fro VGA etc...

That is one of the reasons we are going to do more testing with our monitors.

If you need more help, I may be able to help you cheat a little depending on the monitor you have??

Rick Nieman
Nieman Video Displays
519-621-1722

[Level42]

Hi Nick, thanks for the reply.

I wonder with what value resistors the inputs on your monitors are terminated ? I know more recent monitors (like some Hantarex) have switches to change the input impedance according to what is needed.

As I mentioned, I'm not actualy using an open frame ("real" arcade) monitor on my Galaxian, but a used TV. Since I live in Europe "real" monitors are both very hard to get and extremely expensive. A regular TV however has a SCART connection with RGB inputs. Following this, the TV acts just like any "real" (arcade) monitor (CGA, 15 Khz). New 19" TV"s are available here for around €100,- (about $125,-)

Re. your tests with mame: I use a real Intervideo (=Hantarex) monitor in my MAME cab with an arcadeVGA card from Ultimarc and their J-pac. The arcadeVGA is a regular PC videocard that has modified firmware on it, so it always generates 15 kHz signals, right from boot-up. The J-pac is for connecting a standard Jamma loon to a PC, but as an extra it has a video amp on board that boosts the video signals from 0,7 to 5V.

However, on my Intervideo monitor I have the feeling that the signal is too strong. It might be that this monitor was configured for lower level input....but I didnt  check it out yet. I'm just not sure exactly what model I have....will check that out asap and let you know.

[blueznl]

Level, is that a 'Hantarex Polo'? I just got my hands on one, but haven't tested it yet. I first have to get it out of the cab it's in, and clean it up. And yes, I'm in europe as well. Ooops. Sorry for hijacking this track 

Re. video levels: why not just empirically change the resistors? On a few attempt's you'll get it right  Hopefully 

[Rickn]

Look at the video inputs for a resistor that goes to ground, usual values 75 ohm for VGA, 390 or 1K for Standard or mid res.

You can play with them, hopefully they work??

Not so sure as there is a big difference between the .7 volts you likely have and the TTL level 3~5 volts the monitor would like to have??

Rick

[Level42]

Level, is that a 'Hantarex Polo'? I just got my hands on one, but haven't tested it yet. I first have to get it out of the cab it's in, and clean it up. And yes, I'm in europe as well. Ooops. Sorry for hijacking this track 

Re. video levels: why not just empirically change the resistors? On a few attempt's you'll get it right  Hopefully 

No, it's a much "older" monitor. It's label actualy says Intervideo, but AFAIK that is the same as Hantarex. I should have some pictures.....I'll check and post here.

Yeah I could use some pots as well

[Level42]

Look at the video inputs for a resistor that goes to ground, usual values 75 ohm for VGA, 390 or 1K for Standard or mid res.

You can play with them, hopefully they work??

Not so sure as there is a big difference between the .7 volts you likely have and the TTL level 3~5 volts the monitor would like to have??

Rick

Yeah, the SCART is always terminated with a 75 ohms on the TV (input) side to ground.

About the voltage levels, 5V is still more than 7 times the expected value at those inputs.

But still, I don't want to blow up my "new" TV. When you check schematics on the TV's with a SCART connector, you can easily see that apart from some small resisitors and diodes the signal goes directly into the video processing IC.

F.I., in one of my TV's there's a Philips TDA8362 that is the "Integrated PAL and PAL/NTSC TV processor". The only thing this still does when using RGB is amplifying the RGB signals based on the contrast and birghtness settings. I checked the datasheet and the absolute maximum on the inputs is specified as 0,8Vpp. The outputs are at a 4Vpp level, so that's actualy less than what I would be inputting ! I bet the TDA8362 will give up sooner or later. (Even though it's a Dutch produce )

On the Intervideo/Hantarex in my MAME cab, I can see that when displaying windows (lots of white), the screen seems over-saturated. So there, it is probably to high levels being input.

I guess I should just check the schematics of that monitor I saw that have switchable input levels because that's actualy doing what I need it to do

I may also have an oscilloscope soon (an oldy, but who cares so then I'm able to measure stuff a bit...

[Level42]

OK, I just "identified" my Intervideo monitor, this is it:

http://www.jomac.net.au/inervideo_vp.jpg

Obviously it is NOT a Hantarex ! The CRT is Videocolor=Philips.

I need schematics !

[Level42]

O well, today I took the plunge and simply removed the serial resistors from the SCART RGB input lines and ......it looks great. There may be just a timy little "overpower" but it's not bad and easily corrected with the TV's brighness and contrast controls.

 I don't have the scope yet, so I put my DVM in Vac and measured the outputs......and the effective value were quite low. So I thought I would take the risk. Picture is great now ! Just need to get rid of the continuous on-screen selected channel number and some fine adjusting of size and position.