CXA1645 and bad CVBS output

I have this el cheapo rgb encoder board with a CXA1645 compatible chip (don't know if it is a cxa for real or one of the other pin compatible chips bc the top of the chip is sanded off).

Bottom line - the CVBS(composite) video output looks like shite. Rolling pic, rainbow-like coloring in whites...

I originally thought that this was because there was no Y-trap. Now I see that there is a Y-trap similar to what is described in the CXA1645 datasheet, but not exactly. The datasheet says that you should use a capacitor and inductor coil in series to ground on pin 17. The illustration clearly shows: pin 17 ---> 28pF cap -----> 68uH inductor ---> ground

my board has: pin 17 ----> inductor ----> cap. ----> ground

Could placing the inductor before the capacitor cause problems like this?

Also there is much talk in the pdf of isolating Vcc1 from Vcc2, and also GND1 and GND2 to minimize risk of oscillation. They do not seem to be isolated at all on this board, I get complete continuity (no resistence) between Vcc1 and Vcc2, also GND1 and GND2. If they are not isolated I could easily see how unwanted frequencies could crossover from the SC (subcarrier) input section to the video output section. I'm not even sure that the Iref, Vref, or Yclp are connected to anything, i'm still trying to trace everything.

This is the encoder board: http://www.highway.net.au/parts/converters/1865.html

No I did not pay $85USD for it I got it somewhere else much cheaper

If anyone out there with lots of CXA1645 experience could help me a bit with fixing this I'd really appreciate it. Please no "Why don't you just use the s-video?" posts sometimes composite is a necessary evil

cheers,
-DT

I've been building my own encoders with that chip for a while now and I can never get good composite off that chip. And I've tried that exact Y-trap and it didn't do anything for me. I may try again now that it's come up.

I'm thinking about just not using this encoder anymore, save it for some other project. I have all the parts to build an AD725 board w/ external Y-trap (actually enough parts for several). Just lazy I guess, plus now I'd like to know why the composite looks so horrible on this when I've heard sooooo many things about how GREAT! the cxa1645 is. Actually the s-video is not all that hot on this board either.

I suppose if you follow all the strict rules in the datasheet you could get awesome composite and s-video from it. The AD725 is just so much easier!!

-DT

I don't think CV04 uses CXA1645.

I have used these encoder for a long time before I switched to Neobitz for it component output. The S-Video is perfect, in fact is on par with the Neobitz S-Video out and better than Neobitz Composite video.

Recheck your wiring to the encoder. The encoder should not share its gounding with other GND. For Example, on your PSU

AC AC 5V GND 12V -5V GND GND
| | |
To JAMMA ------- ------------------To Encoder

Also, remove the molex and soldering directly on the encoder itself won't do much good, the encoder has a middle layer and it is difficult to "grab" properly. Use the original wired molex supplied with the encoder for it.

One of the best encoder I ever used and best of all, it is cheap!

The AD724/725 are excellent encoders for MVS but shit with many other boards, if you can get MK2 or Raiden to lock on any TV your a better man than I Gunga Din.

All of you are cxa1645 haters, I have a jrok encoder and 2 back ups that I build my self using the 1645 and the composite pic looks good.

doggydodomi said:

I don't think CV04 uses CXA1645.

I have used these encoder for a long time before I switched to Neobitz for it component output. The S-Video is perfect, in fact is on par with the Neobitz S-Video out and better than Neobitz Composite video.

Recheck your wiring to the encoder. The encoder should not share its gounding with other GND. For Example, on your PSU

AC AC 5V GND 12V -5V GND GND
| | |
To JAMMA ------- ------------------To Encoder

Also, remove the molex and soldering directly on the encoder itself won't do much good, the encoder has a middle layer and it is difficult to "grab" properly. Use the original wired molex supplied with the encoder for it.

One of the best encoder I ever used and best of all, it is cheap!

Click to expand...

My JAMMA loom came with the correct RGB+gnd+s connector to match the CV-04 input. What would be the point of removing this??

If you look up the pinout for the cxa1645, then trace each of the pins with a multimeter (I just did this) you will find that each pin matches the pinout/schematic in the datasheet. So it is either a cxa1645 or a pin compatible chip like the Mitsumi MM1268.

As for the s-video being better...yes I am aware. that is exactly why I said don't tell me the s-video is better. Once, I started a thread about how to implement a luma trap, people kept posting "Why bother with a luma trap when you could just use the s-video?" @%$&!!

Sometimes I only have access to a TV with composite inputs and the composite out on this encoder sucks...whole point of the thread. That and I would like to learn how to fix it.

I do have the board on it's own ground although that won't do much good because it is still grounded to the MVS board through the RGB connector. Also, it looked the same in the first supergun I built. Completely different power supply. The scrolling/bad coloring/etc. applies to all boards I own mvs, soul edge, cps2, even red clash.

cheers and sorry about the rant above,
-DT

ttooddddyy said:

The AD724/725 are excellent encoders for MVS but shit with many other boards, if you can get MK2 or Raiden to lock on any TV your a better man than I Gunga Din.

Click to expand...

Heh, I was about to suggest adding the c-sync after the 724/5. But I believe that won't even be possible because the 724/5 needs the sync signal for color burst timing, etc.

Have you tried splitting the c-sync into separate H and V sync before adding to 724/5? Fairly easy to do if you have a lm1881 and a couple of gates laying around. Just a shot in the dark, i've never used a 724/5 with split sync before.

cheers,
-DT

Already tried seperating C Sync to H V, still no go.

I got another theory to get the AD725 to work on more board, I post result when done.

dogtoy said:

My JAMMA loom came with the correct RGB+gnd+s connector to match the CV-04 input. What would be the point of removing this??

If you look up the pinout for the cxa1645, then trace each of the pins with a multimeter (I just did this) you will find that each pin matches the pinout/schematic in the datasheet. So it is either a cxa1645 or a pin compatible chip like the Mitsumi MM1268.

As for the s-video being better...yes I am aware. that is exactly why I said don't tell me the s-video is better. Once, I started a thread about how to implement a luma trap, people kept posting "Why bother with a luma trap when you could just use the s-video?" @%$&!!

Sometimes I only have access to a TV with composite inputs and the composite out on this encoder sucks...whole point of the thread. That and I would like to learn how to fix it.

I do have the board on it's own ground although that won't do much good because it is still grounded to the MVS board through the RGB connector. Also, it looked the same in the first supergun I built. Completely different power supply. The scrolling/bad coloring/etc. applies to all boards I own mvs, soul edge, cps2, even red clash.

cheers and sorry about the rant above,
-DT

Click to expand...

Well, the only reason the S-Video was mentioned is that you mentioned that "it wasn't even that great". To which I would have also said that CXA1645 gives me great S-Video too! But horrible composite.

Regarding the sync signal for the AD724/5 chips, this is something I have covered here before with the NeoBitz. Separating the sync signal makes the AD chips work much better with some JAMMA boards. But interestingly, the AD works perfectly with Atomiswave while the CXA chips do not.

D-Lite said:

Well, the only reason the S-Video was mentioned is that you mentioned that "it wasn't even that great". To which I would have also said that CXA1645 gives me great S-Video too! But horrible composite.

Click to expand...

The S-video is good with this board, but it's not eye poppingly great. It could be better, and I think the very minor problems with the s-video have to do with the board design and not the cxa1645.

Regarding the sync signal for the AD724/5 chips, this is something I have covered here before with the NeoBitz. Separating the sync signal makes the AD chips work much better with some JAMMA boards. But interestingly, the AD works perfectly with Atomiswave while the CXA chips do not.

Click to expand...

Guess I'll have to order an lm1881 then Does jameco have these?? I need to order some eproms, i'll try to get an lm1881 with this order. So i'm gonna build the 725 encoder this week. Wish me luck!

thanks all!
-DT

Some questions off topic since that RGB to VIDEO board was mentioned...

how about using this board http://www.arcademvs.com/accesseriors/A-22.jpg to convert the RGB from a PCE (Turbo DUO) to S-Video.. Would I get a nice clean pic?

I've also tried to connect the Turbo DUO RGB with a RGB amp I built:
http://members.core.com/~drtooth/CONSOLES/DUO_RX/DUORX_RGB4.jpg

to a Gauntlet Dark Legacy cabinet arcade monitor Neotec
http://www.neotecgraphic.com/detail.asp?TABLENAME=OSD_TRISYNC&ID=2

500DX series monitor with no success. The monitor will not sync. Do I need a sync separator?

US SNES console works fine with the Composite Sync pin. But the DUO does not show any picture. Its funny when I conect the duo to this other sony RGB 19" monitor via RGB it works fine:
http://members.core.com/3D/FE/drtooth/CONSOLES/SONY/PVM2RGB/PVM-20N5U.jpg

Sony PVM20N5U with RGB added.

Thanks for any suggestions.