A1200 video problem

[spaceman88]

Well I got my Scala issue sorted, now things are looking serious. I have no composite video out. RGB works, sound works, A520 video works. I would just use the A520 but with what I'm an doing I need a monitor connected to the RGB output. Is there a common part? Bad capacitors? Ideas?
Thanks

[spaceman88]

Is it a pal/ntsc problem perhaps?

Doesn't appear to be. I booted into both modes and tried a TV that will display NTSC and PAL but no results.

[spaceman88]

Once, I had an A1200 model that it could display from RGB PAL signal but from the composite output was just b/w :-/

If your running PAL on NTSC or vice versa sometimes you will get a b/w picture. I'm going to try and find some A1200 schematics and trace the signal with my scope. I also ordered some caps from Cosno.

[spaceman88]

I finally took my 1200 apart and traced the video signal with my scope to the "-" side of C237 but not on R2340. My Ohm meter confirms the trace is open. I don't see the trace, maybe it runs in the middle of the board, which brings me to C236, a nearby surface mounted cap that was leaking (of course). I removed it and by one of the pads it looks like there is a hole in the board. Does this stuff usually eat right into the board? I can fix the video with a jumper. What should I put on the board to stop the corrosion? So far I just cleaned it with Iso-alcohol.

[spaceman88]

I have used vinegar before on an A4000 battery issue, but I was unsure of the capacitors chemistry. I dug out a bino-microscope (eyes not what they used to be), it appears the liquid ran down a VIA and did damage on the underside of the board. I repaired the board with a small wire. I'll try to attach a before and after picture and yes I know the pictures are VERY bad :-).

[spaceman88]

You need to cover that new trace up with some conformal coating or clear nail polish even. It will corrode badly if not.

Yeah, I had some "stuff" from my TV fixing days in the 90's, but it dried up :-). I repaired a lot of broken boards back then, people were always dropping their TV's for some reason!! The traces were much larger on TV's back then than on a 1200 and my eyes were better. I started removing the other caps (two soldering iron method), but I'm not sure how I'm going to get the one beside the keyboard connector, very close to the socket.

[spaceman88]

Just to close out the thread, I was able to fix the video problem and replace the caps, so I should be good for another 20 years :-). Thanks to everyone who gave suggestions.