gbs-control VGA 640x480p60 source downscaled to 15khz

I just got one of these boards built and trying to downscale a VGA source 640x480p60 to 15khz in an arcade cabinet. This is what I end up with (video):

https://www.dropbox.com/s/mfsxjr30ulgk7wr/PXL_20210219_054200629.mp4?dl=0

The board builder told me that downscale only works with 480i which I confirmed by inserting a GBS-8100 480p to CGA 480i conversion PCB into the chain. The image is very washed out (white) even with the lowest of gains in the gbscontrol board. I rather not use the GBS-8100.

Any ideas?

Feb 19 '21 19:02 datamattsson

I'm having the same issue and I think is the same as in https://github.com/ramapcsx2/gbs-control/issues/128

and the same problem solved on input here: https://github.com/ramapcsx2/gbs-control/issues/152

As you can see for 480p it seems you have to convert RGBHV to RGBS on the input.

I will try to add the XOR sync combiner but I think this may be the solution

Mar 15 '21 07:03 radabass

Thanks! This looks promising. Any "over-the-counter" solutions for RGBHV to RGBS? All I find is schematics.

Mar 15 '21 14:03 datamattsson

Hi @datamattsson,

It is confirmed, I've tried yesterday on a livestream to implement the sync combiner circuit and it works flawlessly.

The source was a 480p Dreamcast providing RGBHV and the gbs-control was downscaling to 15kHz 240p

As you can see from the live event screenshot without the sync combiner I have the same problem as you:

And after implementing the XOR Sync Combiner https://www.epanorama.net/circuits/syncbox.gif

Everything works as expected, I am using an OSSC because I don't have a crt on my minilab but the ossc clearly states it is a 15kHz signal progressive outputting from gbs.

Mar 16 '21 08:03 radabass

Would love to see an image of how you wired it up. It's usually easier to tell than by just looking at a schematic.

Mar 16 '21 21:03 Danexmurder

Seems like this would potentially do the trick using the parts mentioned in the schematic.

https://oshpark.com/profiles/Gcharlie84

Mar 16 '21 21:03 Danexmurder

Here you have the wiring, I put this board inside a DB15 female connector and used the P11 header.

sync_combiner_bb

3.2V/3.3V sync with these values.

Mar 18 '21 13:03 radabass

Someone build me one of these! :-)

Mar 18 '21 17:03 datamattsson

@radabass I'm getting the components together for the diagram you have posted above, but having trouble finding the exact measurement capacitors. any guidance or part numbers? can I go more or less? on which numbers? i'm a bit of a noob.

i have done a bunch of build but always of kits with components ready to go, as well as a bunch of console modding and fixing. and of course the GBS build.

thanks!

Mar 18 '21 21:03 gingerbeardman

@gingerbeardman, sorry for the delay, for the input resistors and caps I can see on the other schematics 2.2k and 22uF 10v (Electrolytic), I've tried these values too and it works flawlessly, don't forget to add the output resistor to lower 5v output level! In my case I've used 470ohm.

I will try to upload some pics from the temporary build until the custom PCB arrives.

I've compared the 240p outputting from the Dreamcast via scart and the gbscontrol 480p to 240p and it seems like the black lines between scanlines are a lot thicker than expected, also some text is not readable, I can see in the menu options for scanlines (I suppose by scanlines they reffer to the black lines between real scanlines)

Is there any way to disable the black "scanlines" completely in 240p?

(this comparison was done on a 15kHz TV with scart input, the GBS-control output to an UMSA from ArcadeForge )

Mar 22 '21 11:03 radabass

I have some pictures of the temporary setup, this works as intended.

The only problem I see are the big fat black lines between scanlines, is it possible to change them somehow?

Mar 25 '21 10:03 radabass

I wanted to report back that I didn't have any luck using this board.

https://oshpark.com/profiles/Gcharlie84

There was no BOM listed so I set it up using all the parts from this.

https://www.epanorama.net/faq/vga2rgb/vga2rgbs_ttl.gif

Any advice would be much appreciated.

Apr 08 '21 05:04 Danexmurder

@Danexmurder this adapter seems to deliver power from DSUB pin 9. Most of the devices don't use this pin at all and also don't deliver/consume power on that pin.

Apr 08 '21 08:04 necroware

I think @necroware is right, @Danexmurder you can try cutting the trace of pin 9 and soldering the 5v from the GBS to the chip VCC (or 3.3v, check your IC manual), I think some attenuation for the output of the IC may be good using a resistor on the 13th pin VGA output, I lowered the output to around 3.3v just in case but maybe it is not required for this board.

Apr 08 '21 08:04 radabass

Hello, I have compile some configuracion for XBOX 360 and Dreamcast using the some information on web, I share with you please give me feedback

arcade-project.xlsx gbscontrol.zip

May 27 '21 01:05 mmartinezespichan

@mmartinezespichan I have no idea what your files are trying to show. can you please explain?

May 28 '21 10:05 gingerbeardman

Yes, I'm building a case for the GBSControl, I'll use for xbox 360 and dreamcast, for that I need to downscaled to 15hz and rescale to 240p.

In order to set the goal, I have read that I need to first have another input for RGBHV in order to support it in the GBS-8200.

Also, I need and output for my arcade Sega Astro City, I did the following schema, but I don't know If It is only the way to get it or if I have an issue with the schema that I need to consider.

imagen

For the base, I had modified a 3d base for GBSControl model, I'll share in other to understand the distribution for the db15 input ouputs. Also, If it works for your projects.

imagen gbscontrol8200-basev2.zip