Neo Geo CD Front Loader CSYNC Mod

Dr No

n00b
Joined
Sep 2, 2002
Posts
25
Hey Guys,

I recently installed the Furrtek SD Loader on my NGCD front-loader (it was sitting in storage for years!) and discovered that the unit suffers from the same lack of csync when using its RGB output that is described and fixed here: https://retro.supermegabyte.com/2019/03/25/fixing-rgb-output-on-the-neo-geo-cd/

Unfortunately, the pcb layout of my front loader is different than the layout pictured in this tutorial (which was for a top loader). Can anyone point me in the right direction for instructions on how to perform the csync mod on a front loader? I've confirmed that the OSSC can't establish sync with this unit (in its stock form) when connected via an Insurrection Industries RGB SCART cable.

Thanks!
 

Burning Fight!!

NIS America fan & Rent Free tenant
10 Year Member
Joined
Jan 12, 2014
Posts
4,340
You need to find the video encoder chip, look at the chip's datasheet to see which pin gives CSYNC out, and wire that to the appropriate pin on the connector. Nothing too complicated. But do you really need that for your setup? On my NGCD I only had problems trying to tap CSYNC directly, I ended up having to tap S-Video Luma at the end like the article described, which actually might be easier to do.
 

Neo Alec

Ned's Ninja Academy Dropout
20 Year Member
Joined
Dec 7, 2000
Posts
11,929
The guide you linked ends up with sync-on-luma, not csync. I'm not sure if csync or sync-on-luma will actually fix your problem. The more common issue with Neo Geo on the OSSC is that the TV won't accept the sync rate, not how clean the signal is.

No one has figured out why the original csync mod doesn't work right. You might get lucky and your upscaler will do fine with the irregular sync it outputs (my Framemeister worked fine with it). But then I connected it to my CRT and had the same problem others have reported where the video comes and goes (my result was identical to the one shown in the video from that guide).

I ended up having to switch both my toploader and CDZ I modded to sync-on-luma.

If anyone can figure out what is going on with the csync on these systems, I'd love to know.
 

Dr No

n00b
Joined
Sep 2, 2002
Posts
25
Thanks guys. Yes I intended to do the mod using the sync-on luma method, sorry for the misstatement about csync. My issue is figuring out which traces on the NGCD front-loader pcb to cut, as the pcb circuitry on the front loader is different than what's pictured in the posted tutorials. And I did try the recommended adjustments on the OSSC for the neo geo odd sync rate -- it works fine with my MVS output but not with the NGCD.

If useful I can post a picture of the front-loader pcb if that will help figuring out which traces to cut.
 

Dr No

n00b
Joined
Sep 2, 2002
Posts
25
Here’s a pic of the relevant part of the pcb — you can see that the traces run differently than shown in the linked tutorial. I just want to be sure before I start cutting traces!
 

Attachments

  • 42CEB869-1576-4A34-A9C2-E359A9AF5CCB.jpeg
    42CEB869-1576-4A34-A9C2-E359A9AF5CCB.jpeg
    1.1 MB · Views: 4

maki

Edo Express Delivery Guy
Joined
Jan 1, 2022
Posts
332
You can restore CSYNC on Font/Toploaders with 2 Resistors and one Cap.

Pin 10 of the CXA -> 10K R in Series, then a 1830 R to GND, from the 10K to a 470uF cap (positive leg), negative leg to Pin 7 of the AV Port.
I cut the leg of Pin 7, so I do not need to reroute the Compsite Video signal, works for Front and Toploaders.

That will yield a clean CSYNC with 0.6Vpp.
PXL_20230106_105625041.jpg

Screen Shot 2023-01-21 at 1.28.24 pm.png

Thats the CSYNC "Mod" done to MVS btw. when consoling them or building a super gun for 75Ohm equipment (consumer TVs), take TTL CSYNC and just add attenuation.


No need for Sync On Luma at all, when there is plain old CSYNC around.
 
Last edited:

Neo Alec

Ned's Ninja Academy Dropout
20 Year Member
Joined
Dec 7, 2000
Posts
11,929
You can restore CSYNC on Font/Toploaders with 2 Resistors and one Cap.

Pin 10 of the CXA -> 10K R in Series, then a 1830 R to GND, from the 10K to a 470uF cap (positive leg), negative leg to Pin 7 of the AV Port.
I cut the leg of Pin 7, so I do not need to reroute the Compsite Video signal, works for Front and Toploaders.

That will yield a clean CSYNC with 0.6Vpp.
View attachment 62638

View attachment 62639

Thats the CSYNC "Mod" done to MVS btw. when consoling them or building a super gun for 75Ohm equipment (consumer TVs), take TTL CSYNC and just add attenuation.


No need for Sync On Luma at all, when there is plain old CSYNC around.
The 1830 resistor to ground is a new addition, so I might try that if I can find time. Thanks!
 

maki

Edo Express Delivery Guy
Joined
Jan 1, 2022
Posts
332
The 1830 resistor to ground is a new addition, so I might try that if I can find time. Thanks!
I had two resistors here, 1.5k and 330.

I've measured the signal under load to determine the value 1.8k-ish against ground, its to reduce the voltage to 0.6Vpp

The 10k Ohm I've stolen from other peoples design for MVS ( https://oshpark.com/shared_projects/R8NJ9UQ4 its R1 there, 9.53kOhm), it limits how much current can flow, so to not drag the TTL CSYNC down too much.

A simple resistor network, one value taken from a known good design, the other one I've measured out with a resistor decade and an oscilloscope.
 

Dr No

n00b
Joined
Sep 2, 2002
Posts
25
Maki, that's very helpful. If I'm understanding this correctly (sorry if this comes across as newbie-ish), you are running a 10K Ohm resistor from pin 10 of the CXA to the positive leg of a 470uf cap (any particular voltage required for that cap?), and then from that same positive leg you ran two resistors (in series I assume?), 1.5K ohms and 330 ohms, to ground. And the negative leg of the capacitor was connected to pin 7 of the AV port, which you cut. (I love the idea of cutting pin 7 rather than cutting the traces to that pin, especially on the front loader pcb where there are other thin traces very close to what I would need to cut!)

Your post says you used two resistors (1.5K and 330) from the cap to ground but I only see one in your pic (and the value is obscured) -- is the second resistor not pictured or maybe I'm missing it?

Lastly, is there any advantage to using csync (which requires adding the 3 resistors and the capacitor) rather than just stealing the sync on luma with a single wire to pin 7?
 

GohanX

Horrible Goose
20 Year Member
Joined
Sep 28, 2001
Posts
12,490
Before you start hacking up the system, do you have a setup that actually needs csync over grabbing sync from composite video, or are you just doing it because the usual gang of idiots online says it's better? It doesn't matter in most setups, and it's easier to rewire a RGB cable than modify a system.
 

Dr No

n00b
Joined
Sep 2, 2002
Posts
25
Good question. I tried running the stock NGCD AV port output to my OSSC using an Insurrection Industries Neo Geo RGB cable and couldn't get sync (using the same OSSC settings as I use for my MVS board thru a HAS supergun, which worked fine). I also tried the same NGCD output through a Framemeister (and a Euro RGB to JP21 adapter) and got a garbled picture. From everything I've read, this mod is necessary for the OSSC to get sync from the NGCD, which seems to be borne out by my results. Make sense?

BTW, the S-Video output of the NGCD looked surprisingly good, even on an 85" QLED screen. I just figured I'd get even better performance with RGB output.
 

Neo Alec

Ned's Ninja Academy Dropout
20 Year Member
Joined
Dec 7, 2000
Posts
11,929
You should be getting a picture on the Framemeister with sync-on-composite. It sounds like there's a different problem.

Did you try setting the sync mode on the Framemeister to Off?
 

Dr No

n00b
Joined
Sep 2, 2002
Posts
25
I'm pretty sure I did. I did get a picture but it was full of video noise and the colors were way off. This may well not have been a sync issue but something else -- a Framemeister setting that needed to be tweaked, or maybe an issue with the RGB to JP21 adapter. Right now my NGCD is in pieces while I finish recapping it so I can't test it out again right away. But in any event I'm most interested in getting the unit to work with my OSSC (so it can integrate with the rest of my rig) so unless someone has another way to do that I'm assuming I need to do one of the sync mods?
 

maki

Edo Express Delivery Guy
Joined
Jan 1, 2022
Posts
332
I tried running the stock NGCD AV port output to my OSSC using an Insurrection Industries Neo Geo RGB cable and couldn't get sync (using the same OSSC settings as I use for my MVS board thru a HAS supergun, which worked fine).
That is not related to CSYNC or not, thats the "hiccup" in the Sync Signal of all NGCD and some MVS, a CRT doens't care about that hiccup, the OSSC can't sync on it though, unless you change the config slightly.

Try these settings in the OSSC Sync menu:
HSync tolerance >= 10us
H-PLL pre coast >= 3
H-PLL post >= 3

The 1.5kOhm + 330 Ohms is how I got the 1830Ohm, I'm sure a 1800Ohm will do just fine.
 

Dr No

n00b
Joined
Sep 2, 2002
Posts
25
Thanks -- I hadn't heard about that "hiccup" issue before. I'll give those OSSC settings a try when everything is reassembled and report back.
 

Neo Alec

Ned's Ninja Academy Dropout
20 Year Member
Joined
Dec 7, 2000
Posts
11,929
I'm pretty sure I did. I did get a picture but it was full of video noise and the colors were way off. This may well not have been a sync issue but something else -- a Framemeister setting that needed to be tweaked, or maybe an issue with the RGB to JP21 adapter. Right now my NGCD is in pieces while I finish recapping it so I can't test it out again right away. But in any event I'm most interested in getting the unit to work with my OSSC (so it can integrate with the rest of my rig) so unless someone has another way to do that I'm assuming I need to do one of the sync mods?
CSYNC probably won't help for that. All CSYNC is good for is reducing noise from an impure sync signal.
 

maki

Edo Express Delivery Guy
Joined
Jan 1, 2022
Posts
332
Thanks -- I hadn't heard about that "hiccup" issue before. I'll give those OSSC settings a try when everything is reassembled and report back.
its documented here:

without these setttings, no pics on the OSSC

CSYNC itself is really just a cleaner Sync signal that won't pollute the RGB channels like Composite Video does (jailbars etc.), also CSYNC is required by some pro-gear (Extron Crossmatrix switchers etc.) and some PVM/BVM.
 
Last edited:

Dr No

n00b
Joined
Sep 2, 2002
Posts
25
I thought I’d report back that, as you all suggested, applying the OSSC settings recommended above enabled me to sync with the OSSC using the unmodified NGCD RGB output. Seems like there’s a lot of misinformation out there on the need to perform the sync mod, at least when using an OSSC. Glad I checked here first before modding the unit.

I will say, however, that while the RGB image is certainly sharper I’m not sure it’s visually more pleasing than the s-video output, at least on my very large QLED screen. Next step is to dig into the OSSC settings to see if I can improve the image.
 

Neo Alec

Ned's Ninja Academy Dropout
20 Year Member
Joined
Dec 7, 2000
Posts
11,929
Thanks for the update! Glad you got it working. It's a shame that people are suggesting the CSYNC mod for the OSSC when it's not needed.

What's the problem with the image though? Did you dowload the suggested profile for the timing for Neo Geo? It should look better with the correct pixel integer scale. If the image is noisy or has jailbars, the CSYNC mod, or a sync stripper in the pipeline might help with that.

I still want to try maki's suggestion for my already modded system to see if I can get CSYNC. If so, retrorgb's page is badly in need of an update.
 

Dr No

n00b
Joined
Sep 2, 2002
Posts
25
Hey, sorry for the long delay in responding (I’m having some issues with getting notifications of new posts)!

To answer your question about my problem with the image, because the RGB image is so much sharper it makes the image (at least on an 85” screen) very blocky. I’m pretty sure I used Firebrand X’s Neo Geo settings for the OSSC, but will double check those settings and, if necessary, will see if I can add some sort of smoothing to make the picture more pleasing (haven’t gotten around to that yet). Or maybe I just need to go with a smaller screen :-)
 

maki

Edo Express Delivery Guy
Joined
Jan 1, 2022
Posts
332
@Dr No the "hard" pixels are normal with the OSSC, the RetroTink 5 has better filters for softening, using old arcade HW or consoles on modern TVs requires compromises, and a CRT will soften the picture by itself, thus improving it, 240p really isn't that good if you can see every pixel on a modern TV/LCD.

If your TV can manage, you can try the passthrough option on the OSSC, no pic improvement/sharpening, just passes it through.
My Dell can manage that, not sure about your TV, its a really weird resolution, but if it works, it looks quite soft.
Easiest way to soften the pic on a OSSC is to turn the LPF on the signals to 9 MHz IME.
 

Neo Alec

Ned's Ninja Academy Dropout
20 Year Member
Joined
Dec 7, 2000
Posts
11,929
Hey, sorry for the long delay in responding (I’m having some issues with getting notifications of new posts)!

To answer your question about my problem with the image, because the RGB image is so much sharper it makes the image (at least on an 85” screen) very blocky. I’m pretty sure I used Firebrand X’s Neo Geo settings for the OSSC, but will double check those settings and, if necessary, will see if I can add some sort of smoothing to make the picture more pleasing (haven’t gotten around to that yet). Or maybe I just need to go with a smaller screen :-)
Those razor sharp pixels are what you buy the OSSC for.

May I suggest smearing Vaseline on the screen?
 

Dr No

n00b
Joined
Sep 2, 2002
Posts
25
Got some funny looks from the sales clerk at CVS when I tried to buy enough Vaseline, but unfortunately they didn’t have enough in stock 😁

So looks like I’ll be giving Maki’s suggestions a shot and I’ll report back!
 

maki

Edo Express Delivery Guy
Joined
Jan 1, 2022
Posts
332
the OSSC is know for its "hard pixels", if you really want a smoother picture, try the RetroTink 5 Pro
 
Top