Dim patch on SE/30 screen?

[eharmon]

My SE/30 has developed a dim region on the screen which doesn't match any of the Dead Mac Scrolls diagnostics. I'm getting some occasional flickering, so I definitely think the analog board is due for a recap, but this behavior is curious.

Essentially, about 25% of the left side of the screen is dimmer than the rest, at any brightness level. It doesn't seem to vary as screen contents change, and it's maybe 15% less bright. I'm also having linearity issues, with some stretching in the left 10%, and I think the system got a good knock at some point, because the adjustment magnets on the yoke are slightly out of alignment as well. But that shouldn't cause this.

In short, time for an overhaul. But I'm not sure what to chase on the dim region, any ideas?

 

[Callan]

Dead mac scrolls was written before all these caps went bad. That's a common issue with monitors, and it's usually caused by a bad cap. When was it last capped?

 

[MIST]

Stretching means that the beam runs faster over the stretched area. And that in turn means that less electrons hit the stretched area.

The reduced brightness in that area may just be caused by the stretching.

 

[Byrd]

Can you post up some pics over different backgrounds? It could possibly be a degaussing, missing magnet or bad electron gun issue - either way it doesn't sound very healthy and clearly that knock didn't do it any favours. I'd start looking for another CRT longer term.

 

[croissantking]

Can you post up some pics over different backgrounds? It could possibly be a degaussing, missing magnet or bad electron gun issue - either way it doesn't sound very healthy and clearly that knock didn't do it any favours. I'd start looking for another CRT longer term.

With the popularity of the LCD mod for the SE/30, there should be a surplus of old compact CRTs floating around the community - worth posting a WTB request.

 

[Franklinstein]

It's not discolored, is it? Maybe you got a magnet too close to it. Maybe try to degauss it.

Conversely, maybe one of the internal geometry magnets came loose.

 

[eharmon]

Thanks for the suggestions! It needs a recap anyway so I think I'll give that a go first and see where that leaves me. Overall the CRT seems intact (if a bit tired) despite the slightly jostled geometry magnets. The linearity problem specifically is suggested by the Scrolls as a bad resistor, so I figure the solid baseline of fresh caps well help me narrow it down.

 

[smrieck511]

Full recap of the analog board is pretty easy and cheap compared to other restoration needs. No reason not to do that.