SE/30 Jittery video

[BusError]

I recapped my SE/30, reflowed the big connector on the analog board. Deoxed the trim pots...

Machine is stable, but the video isn't! The video 'jitters' a bit left/right -- not necessarily the whole screen, it can be the center of the video while the border stay in place... but it varies a bit... Image is otherwise sharp, and there's no vertical jitter...

Any idea? I haven't recapped the analog board obviously!

 

[Kai Robinson]

This is a job for.... @techknight !

 

[Garrett]

Try replacing the horizonal output transistor!

https://www.digikey.com/en/products/detail/onsemi/BU406G/918378

 

[smrieck511]

If it were me, I'd start by redoing or reflowing the solder joints on the analog board. Then do an analog board and maybe PSU recap.

That way you're at least getting the preventative maintenance out of the way. That normally fixes jittery screens for me but if not, you can dive into testing individual components.

 

[techknight]

Try replacing the horizonal output transistor!

https://www.digikey.com/en/products/detail/onsemi/BU406G/918378

This

 

[BusError]

So, I got my replacement transistors... is there a schematic or a hint on *which* transistor to change, for someone who doesn't know the layout or gory details of how the analog board works?

 

[BusError]

Well that was fun. Anode wire broke in the cup as I pulled the cup out... I thought I was screwed, but I managed to remove the cable from the cup, the glue was pretty weak with age! Cleaned the clip, removed 1cm of extra insulation and reassembled it. As good as new, I hope.

 

[BusError]

In other news, Q2, that famous transistor, was also replaced. Can't test right now as my wife's on a conf call and not going to like if I smoke/trip the place up

 

[BusError]

Ok tested. And that transistor WAS the problem; video is nice and stable now, so the fixed anode cable worked fine...

I probably need to work a bit more on that board, the 4 pin connector is burned as many are, and it could use a new fan, but at least the video is great!

 

[BusError]

Oops didn't last. 10 minutes of stable video and the problem came back :-/

 

[BusError]

So, having replaced the PSU with another, and still having the wavy video issue, that narrowed down the problem to the analog board proper. So I recapped it. I also changed the 4 pin connector housing/plug that was completely perished. I didn't find any obvious 'bad cap' -- definitely not according my Peaks Electronics tester; but after recap, cleanup and new connector, the problem appears to have been fixed!

 

[Bolkonskij]

Hasn't this kind of problem with compact Macs been lamented ever since? I vaguely recall reading about it the first time back in the early 90's in some MacUser (or else) issue. My SE suffers from the same problem. Video jitters for a few seconds and goes back to normal for another few minutes. I'm not as much bothered by it to repair an otherwise perfectly working system yet. Crossing fingers @BusError your fix solved the issue for you