Amiga RGB to S Video & composite adapter

[Chartus]

I built this from a schematic I saw over on the English Amiga Board.  I wanted to get S video working on my 600 and 500.  The problem is that S video doesn't work.  A brief flash of a garbled Workbench screen and then the screen goes black.  Same thing on both computers.  Composite works fine.  Anyone have any ideas about what might be going wrong with it.

Links are below.

eab.abime.net/showthread.php?t=30752

www3.telus.net/narmi/schematic.png

[Illuwatar]

I have used the AD724 in my MiniMig and got it working. You can see it in this schematics:

Schematics of a MiniMig

I'm not really familiar in the RGB-output from an Amiga, but the signal going to pin three (FIN) at the AD724, what is that? In my design, it is connected to a PAL (or NTSC) crystal and a parallell capacitor for picture stability adjustment.

I hope you get this working - the AD724 is a rather simple IC to work with.

[rkauer]

 For the A600 you don't even need the board!

 If you are skilled enough, it's simple to route two wires from the Amiga's video encoder to a S-VHS connector!

 Just put a wire on luma (Y) and other to chroma (C) pins of the CXA1645. Simple, huh? :-D

[Chartus]

Yes I know.  Its mostly for the old Amiga 500 that I have.  I wonder if it is a bad cap going to the s video port?  Colors look good coming out of the composite so That means that the RGB inputs are working. (I think)

[adolescent]

Are you sure your s-video jack/cable is hooked up correctly?  Try running just the luma signal and ground to a RCA cable and see if you get a black and white picture.  Also, have you tried another display?

[alexh]

rkauer wrote:
For the A600 you don't even need the board! If you are skilled enough, it's simple to route two wires from the Amiga's video encoder to a S-VHS connector!

D'oh, not fast enough! I was going to say that.

[Wingnut]

Looks like you built the same circuit that I did.  I had the same problem and I found that the output pins to the s-video jacks were reversed.  Composite jack worked although not as clear as the s-video.  Good luck.

Joe

[Chartus]

Read your post and switched the outputs.  I was in a hurry so I used jumpers to switch them. Pulled the cable from the TV to run a quick check. OK everythings connected again.  Pluged it in the 500 and turned the computer on.   .....Nothing.....oops..... I neglected to plug the s video cable back in the TV.  Powered everything down and plugged it in and  IT WORKS.  It's time to heat up the soldering iron.  

I went back to the ADF for the AD724 chip and if I am reading it right they have the schematics wrong for that part of the circuit.

Thanks Wingnut.

[Wingnut]

Read your post and switched the outputs. I was in a hurry so I used jumpers to switch them. Pulled the cable from the TV to run a quick check. OK everythings connected again. Pluged it in the 500 and turned the computer on. .....Nothing.....oops..... I neglected to plug the s video cable back in the TV. Powered everything down and plugged it in and IT WORKS. It's time to heat up the soldering iron.

I went back to the ADF for the AD724 chip and if I am reading it right they have the schematics wrong for that part of the circuit.

Thanks Wingnut.

Your quite welcome and yes I also concluded the leads are reversed from the ad724.  I built the circuit externally so that I could move it to any Amiga and not have to worry about finding an old 15khz monitor.  Mine worked very well with a cheap lcd (Maganovox TV) and A600.