Where can I tap a sync signal for s-video?

[lastcallhall]

Please bear w/ me - I'm currently one handed and on a lot of pain meds coming out of shoulder surgery...

Last week I decided to build a s-video/composite circuit out of a CXA1645 like I've done at least a dozen times before, only this time I planned on sticking it into a TG-16. I built the circuit, attached the RGB IN locations on the chip to the RGB OUT locations on the TG-16 EXT connector (23A, 23B, and 23C), along with the SYNC IN on the chip to the SYNC OUT on C22. everything is properly attached to their respective components and grounded. In addition, I tapped the Audio from 1A and 1C, and grounded them to the board, as well. There's also a reset button and region chip installed, as well. I powered the console on in s-video and I get audio just fine but no sync on s-video. I try it with composite, same thing. I test it with my turbo booster and I get good video and audio. So, I figure my problem is with the sync pin. After some researching I find that it's actually labeled composite sync, but that shouldn't make a difference, right? Sync should be sync, as far as I understand it. I'm hesitant to take the system apart again, now that everything is soldered and screwed into place, so is there anywhere on the bottom surface of the board that I can tap into?

Thanks!!!

[SignOfZeta]

The only thing you can get from a PCE is composite sync, and it's not the best example of composite sync out there. If it doesn't work for you...sorry, I have no advice as I've had nothing but trouble with it.

[lastcallhall]

Hm. Ok, thanks for the info. I think i'm going to try and tap directly off of the C6260A and see what happens...

[ogre]

To get a good sync for the CXA use a LM1881N. Put the composite video through this circuit and it will output composite sync.http://www.national.com/images/pf/LM1881/00915001.pdf This is needed as the systems own c-sync does not put out a useable signal.

[lastcallhall]

To get a good sync for the CXA use a LM1881N. Put the composite video through this circuit and it will output composite sync.http://www.national.com/images/pf/LM1881/00915001.pdf This is needed as the systems own c-sync does not put out a useable signal.

Fantastic, thanks!

[Keith Courage]

So does this mean by using the said IC and using that signal along with the typical RGB outs you can run it to an S-Video connection? I have also been wondering how to do this myself for a while now.

[lastcallhall]

That's what I'm hoping for...

[lastcallhall]

So, I have a quick question: I understand the schematic except for the RSET pin. What is it, and what is it used for? More importantly, do I need this pin for what I want to accomplish? Thanks!

[bust3dstr8]

Rset=Reset 

[lastcallhall]

Rset=Reset 

That's what I thought, but I never assume anything in electronics, LOL.

Also, I was looking through the data sheet and saw that there's an application circuit diagram below the connection diagram. I'm thinking I should use the app circuit instead of the connection circuit?

Reference: http://www.ti.com/lit/ds/symlink/lm1881.pdf

[grahf]

The connection diagram on page 2 is all you need. I used this chip for my Svideo boards I was making a few years ago. Also, you didn't mention anything about the 3.579 MHz frequency input the CXA1645 needs. I guess you picked up an oscillator? If you don't have that hooked up the circuit won't work. They are available in half size dip packages, like this:

[SignOfZeta]

Question: if I have a JROK or NeoBitz s-video encoder can I just wire that directly to the internal RGB in a PCE or does it need amplification?

[thesteve]

the sync on the TG/PCE is a good signal, its just weak (needs amplification)
i use it on the ad722/ad724 chips for my TE/GT screen mods

[lastcallhall]

The connection diagram on page 2 is all you need. I used this chip for my Svideo boards I was making a few years ago. Also, you didn't mention anything about the 3.579 MHz frequency input the CXA1645 needs. I guess you picked up an oscillator? If you don't have that hooked up the circuit won't work. They are available in half size dip packages, like this:



Yeah I have a half can oscillator on there.

Thanks for clearing the diagram up - I was going crazy trying to find a bi-polar 510pF capacitor.

[lastcallhall]

An update...

This is crossposted from Sega-16.com, so I apologize in advance for any repeats in information.

Long and short of it is, is that I bought a Duo-R a couple months back to replace my TG-16/Turbobooster combo I've had for a little over a year. Well, the Duo is in need of a CD lens replacement, so in the mean time I thought I'd try and mod the TG-16 for s-video and audio out, and see what comes of it.  I was able to look at the documentation shown over at GameSX.com, and from there took the proper signals and fed them into the CXA chip, composite signal included, on top of adding a region chip (Obey chip from BlueBMW and TheSteve from pcenginefx) and reset button. Once I had everything hooked up, I powered it on and got this:


As you can see, the sync signal seems to be trashed. I've done a little research and found the following:

1) The sync signal from C23 on the EXT port is labeled composite sync, as is pin 44 on the 6260 CPU of the TG-16
2) Knowing this, I purchased a LM1881 Video sync seperator, and fed the a) the composite signal from the EXT port, b) the composite sync signal from the EXT port, and c) the composite sync signal from the 6260 into the chip (all at different times, obviously), hoping to get a clean sync signal out of any one of them, but no such luck. This was actually suggested by someone over on the PCEFX forums.
3) I have several 4558D OP AMPs lying around from an earlier CCAM mod attempt, but I'm not sure if I can use them to amplify this type of signal. even so, I don't have the slightest clue as to how to get it done.  

I'd really like to get this up and running (and sold...), but I seem to have hit a wall on this. I'm half tempted to take it to school so I can look at it all in a lab with proper test equipment, but if I could solve it prior to that, it would be even better. So what do you all think? Any help is always appreciated. Thanks!