Using the CXA-1145 as a RGB Amplifier

[RARusk]

After reading the "Source for CXA1645 or CXA2075 chips" topic, I felt I should come forward with my work on the 1145. After many attempts to get a strong transistor based amplifier to work in my N64 without success, I decided to look at my Sega Master Systems since they had a very strong RGB signal. When I opened it up and went backward from the AV plug, I found the CXA-1145 chip. I ended up fragging both my SMS's doing research on it. I eventually found a Sega Genesis model 1 unit and cut a section of motherboard that contained a CXA-1145 and, after studying the traces and wiring it up, got it to work as an amplifier. This chip finally brightened the N64 to the level I desired even though it still looked a little dingy on my MultiSync 3D.

One of my original RGB box "motherboards" can be found here http://xcssa.org/photos/misc-2003-09-15/. The "This is a Playstation to VGA hack....." still hasn't been changed even though the "Playstation" in the picture is my N64. Since those pictures were taken, the box has undergone changes. The pots have been removed (one of them flaked out) and I replaced my 4583 sync chip with the new EL1883 chip (I will have more info on that in another topic). I also restudied the datasheet and fine tuned the 1145.

Go here (http://labwww.csv.cmich.edu/luke/videogames/General/CXA1145.pdf) to get a copy of the CXA1145 datasheet. Go to page 8 to see the hook-up diagram.

The following is how I hooked up the chip to use it as a amplifier:

For the RGB lines, you'll need .1uf caps on the ingoing and 470uf caps plus 75ohms on the outgoing (the 75ohms to ground is an option since I don't have my outgoing lines connected to ground and I have no problems).

Hook up pins 1 and 24 to ground and pins 12 and 19 to +5VDC.

Use a 27k ohm resistor to connect pin 13 to ground (the 10uf cap is optional).

Finally, you will need to connect either composite or horizontal sync to pin 10 to get the chip to work.

Ignore pins 5, 6, 7, 8, 9, 11, 14, 15, 16, 17, 18, and 20.

If you are using composite or horizontal sync from a sync chip (like the 1881) it should be noted that the ingoing composite video to the sync chip should NOT be attached to ground (either with a capacitor or resistor). Doing so can result in interference (ranging from shimmering on the PS2 DVD playback to screen shaking on the TG-16) when using the Commodore 1084 monitor.

The chip can also be multiplexed. I now have another CXA-1145 setup inside my N64 which makes the picture even brighter on both of my monitors when used in conjunction with my RGB box. Of course, this does the same thing to my Genesis and SMS units.

This chip also works on all my other consoles including my SNES and Atari Jaguar.

I also found that it is cheaper to go to a thrift store and acquire Genesis units and hack the chip out than it is to go online and acquire the chips that way.

I have to go now (it is getting late here in Texas) but I will be more than happy to answer any questions you guys may have on how I did this and other RGB hacks.......

[matt]

Nice to see that somebody else has figured this out too

First stumbled across the idea after I put together the S-Video TG16 system mentioned in the other thread.  It turned out that not only did the S-Video look pretty good, but that the RGB just happened to be boosted to exactly the right level and looked much sharper than any other video amps I'd tried.  I figured the CXA1145 ought to do the job just as well as far as the RGB amplification part went, and it did.

I've usually desoldered the chip from the Genny motherboard, cut off the pins, and soldered the components directly to it.  That way you can cover the whole thing in heat-shrink and it's easy to install in areas without a lot of space.

I've found that in most cases, a 100uF decoupling capacitor is necessary in order to avoid corrupted colours or bleeding.

[RARusk]

Where do you put the 100uf decoupling capacitor?

[matt]

Between +5v and ground.

But if your circuit is working fine, there's no reason to fix it.

[RARusk]

Oh yeah, that's right. Duh!

I have a 100uf cap connecting my power trace, which provides power to the 1145 and my EL1883 sync chip, to ground. Works good.

[Endymion]

Robert, dumb q of the day and I hope you don't mind my bumping this one up--ignore pin 11? C-sync out? Was that an oops or isn't this needed... you didn't split c-sync did you?

[RARusk]

Pin 11 is not needed. Just tap into the Composite or Horizontal Sync from either a sync chip or from the console itself and attach to pin 10. Yeah, you can split a line from the sync line to the CXA-1145. That's what I did with the composite sync from the EL1883.

[Guest_RyleFury]

Hello, i have done this amp with Duo-RX, when I start the console, the colours stay 2 seconds and black screen. When i remove 0,1uF caps black screen immediately, please help  

[bigsanta]

Can this be checked for me for any errors,especially the orientation of the polarised caps,also,if using the alternative IC ,the MB3514 http://gamesx.com/temp/e428020.pdf ,would it mostly be the same way to wire it as the sony IC ,except for pin 13 and 14 ?
And as it's for the pc engine(other  consoles aswell ) ,before CSYNC goes to the RGB amp IC ,would it have to be re routed so one way connects to your console's din socket,then to the IC's sync pin (pin 10) ? so your tv ( EURO land )can get the needed C signal along with the RGB lines and the RGB mode voltage  .

Basically to make this more clear,how would i get my needed csync/video signal for my tv /commodore 1084 monitor ,as the above guide only states using the sync  input on pin 10 ,but it doesn't state using an output for the csync/video from the IC, which is needed for RGB to work.

[bigsanta]

Answered my own question by reading the comment above
Just feed the ic the csync/hsync to get the ic to work ,but also have the original csync etc coming from the console source and going straight to the required csync pin on your tv/monitor //

[l_oliveira]

Well I believe that the CXA1145 datasheet mention that it has an DC level restoration circuitry (Aka clamper) built in on the RGB inputs so the outputs are going to be clamped as well. 
But for that clamper to work, you need to feed the chip with CSYNC.

Also special attention need to be given to the CSYNC input of all SONY video encoder chips as it will lose sync and the image will "crap out" if the signal gets past the 2.0v boundary.
(I believe this has to do with the clamper circuitry not operating properly so that's why I am mentioning this detail)


Anyway, the CXA1145 is one of the best video encoders out there. I see no point replacing with the Fujitsu MB3514 or even using one separated from an MB3514 while the 3514 should do the same job.  The only problem with the CXA1145 is that it's annoying to rig properly (you need a ton of analog parts connected to it) but if the circuit is done right the video signal  quality is better than what you could get from the MB3514.

<small hijack, please forgive me lol>
This is the video I got from a self built RGB to S-Video adapter based on the CXA1145 chip:


The only image artifact is a faint dot crawl caused by the chroma carrier oscilator. If I remove the chroma clock the image is SHARP as if it was tied straight to the TV tube but monochrome.
Sorry to hijack the thread a little bit, but... If anyone have an idea how to hide that artifact a bit it would make me really happy...

I also made one with the CXA1645 which is simpler to use as it has no need for an external delay line for the chroma with inductors and capacitors.
That one has the usual "edgy jaggies" from consoles like SEGA as the chroma burst is an square wave as I used an 74LSxx chip to clock the chroma burst  (so the dot crawl artifacts on this one are more like jaggies on edges of red screen sections...) Anyone who plays on composite or S-Video leads know what I am talking about.  Any ideas ?