@mitu that make sense .. thanks for the help.

@DJMoss Adding active cooling eliminated the slowdowns I encountered while running some MAME or NeoGeo games.

​Solved. Bad VGA cable.

here's a couple projects I've done with an LED matrix marquee

RetroPie based ==>https://www.instructables.com/id/Vertical-Bartop-Arcade-With-Integrated-PIXEL-LED-D/

PC Based ==>https://www.instructables.com/id/Arcade-Machine-With-Changing-LED-Marquee/

Here's a guide for setting up this LED marquee and RetroPie ==>http://ledpixelart.com/files/retropie/ .

Runcommand onstart and onend is used here. When a new game is launched, a script runs which passes the rom name to the LED marquee software (http://pixelcade.org) which is then displayed on the panels. Both still image PNGs and GIF animations can be displayed by game.

This project also includes artwork that has been manually re-mastered for 128x32 for that classic 8-bit look. Disclaimer, I'm the creator for this project and sell these as kits.

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I was kind of giving up hope I would get my Howler working on my Pi3. Is there a retro pi image that I can download that will have everything set up? I'm really new to all of this, and I'm also dyslexic so the amount of reading I have to do is pretty daunting.

I'd love to find an image I can just put on my SD card and start going.

Adding this line to Mednafen VB.cfg:

video_refresh_rate = “50.0”

Fixes the timing issue, hope this post helps anyone with the same issue. Runs great now!

( btw, definitely lower the audio_out_rate to around 33200 or something like that, and sample fidelity to lower and add some audio time skew, no framedrops or sound skips now that I could notice even when playing in 3d )

I tested this with success. But I had to set dtoverlay=dpi24 and dpi_output_format=6 to fix some incorrect colors and use the below NTSC 320x240 timing line:

hdmi_timings=320 1 23 30 34 240 1 4 3 15 0 0 0 60 0 6400000 1

@sonpluck

Not a problem.

No one have any idea? Something to do with hdmi timings maybe? How do I solve this?

Now, finally I found another image from the retropie facebook grp... tried it and BAM, no more color problems!!! Wth?
Guess I need to compare the configs since this last one was pre-configured for crt.

Awesome! :) Who would have thought-.. Thanks all!

@nitrogen_widget yeah if you set the pi to 320x240 i believe it will display in 480i. Ugh...

Great, many thanks for the answer! :D I am going to hook up my RPi with HDMI -> VGA and VGA -> Scart so I got scared as I already ordered proper adapters and haven't even thought about it :P
I will try to give some update as soon as I got some time to test it (it would need additional RPi settings to be changed so probably it will take me some time).

@melvin-fox The diagram is on the original post but I will link it here in case you missed it:
http://www.geocities.ws/podernixie/htpc/vga2euro.gif
Anyway you just don't join the Hsync and Vsync together, you must put a 1k resistor on each line before combining them together.