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

[vince_6]

Is it a pal/ntsc problem perhaps?

[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.

[vince_6]

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

[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.

[vince_6]

I use vinegar to clean the corrosion, a drop of WD40 and then alcohol to clean everything :-/

[magnetic]

SEnd it to Acill in usa he will fix it for you. For sure its acid damage.

[paul1981]

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.

I use lemon juice, then clean up with IPA. Small boards you can get under the tap and rinse with water and a soft brush. And yes, it's normal that circuit boards get eaten by leaking batteries and capacitors unfortunately (both alkaline leakages).

[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 :-).

[Acill]

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

[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.

[paul1981]

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.

The top of the keyboard connector unclips and lifts off, giving you a bit more room to get at those particular caps. Then use Kapton tape to heat shield the keyboard connector and the phono sockets. You should then be able to work quite liberally in that area.

[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.

[vince_6]

Great news!!!