STFM VIDEO SYNC FAULT

[czietz]

Coincidentally I ordered the 1 µF ceramic cap that you mentioned just today. So when it arrives and it find the time to change it, I can report if this makes matters better or worse for my STFM. Another information to add: I had some freezer spray to play around. When I sprayed the transistor, the problem reappeared. It went away again when the transistor heated up again to room temperature. That's no big surprise, though, given that such a drastic change in temperatur modify the DC bias and the base-emitter voltage drop. But it means that a warmer transistor (after the computer is on for some time) is better, at least in my case.

In the STFM you worked on today, did you also replace the 33 µF capacitor by 1 µF? Maybe that's too small for some reason? Also I don't have any idea what would cause flickering bars. Vertical instead of horizontal sync issues now? But why?

EDIT: Saw your edit now. So with the larger capacitor everything is fine? With or without changed/added resistors?

[exxos]

Coincidentally I ordered the 1 µF ceramic cap that you mentioned just today. So when it arrives and it find the time to change it, I can report if this makes matters better or worse for my STFM. Another information to add: I had some freezer spray to play around. When I sprayed the transistor, the problem reappeared. It went away again when the transistor heated up again to room temperature. That's no big surprise, though, given that such a drastic change in temperatur modify the DC bias and the base-emitter voltage drop. But it means that a warmer transistor (after the computer is on for some time) is better, at least in my case.

In the STFM you worked on today, did you also replace the 33 µF capacitor by 1 µF? Maybe that's too small for some reason? Also I don't have any idea what would cause flickering bars. Vertical instead of horizontal sync issues now? But why?

EDIT: Saw your edit now. So with the larger capacitor everything is fine? With or without changed/added resistors?

1uF is to low it seems I might have used 2.2uF before, cant remember, I've cheated and just put a new 47uF in there instead. I have the 2.7K on pin 8 as before and everything looks perfect now. I've also changed the 470uF on the composite line, might help with something aswell not sure

[exxos]

I've put current information up on my site. So people can try the mods themselves. This mod is the one which worked best on my machines. There could be other things "wrong" aswell.. but one step at a time.. At least this page is a working start.

http://www.exxoshost.co.uk/atari/last/S ... /index.htm