CRT width

[iantm]

This seems basic, but one of my analog board TDA1170N chips seems to have failed, so I swapped out a different analog board. The geometry was way off. I can adjust the height, the focus, brightness, and the yoke magnets. But the width won't change. Is the pot for the width broken?

I've ordered a couple of replacement TDA1170N chips and a set of CRT universal adjustment tools… I'm hoping that's all it is.

 

[jonschultz]

I'm not too familiar with the TDA1170N, but it looks like it's a vertical deflection IC, similar to other ones that I've seen. I don't think any of the horizontal deflection functions are handled by this IC, so it wouldn't have any effect on the width of the raster (though, a caveat would be that it might have some influence on the pincushion correction, which does modulate width). In any case, I think it's more likely that something else broke in the process of swapping the part. Is the width currently in sort of a normal state, or is it way off?

 

[iantm]

It’s not too far off, but I can’t adjust it at all with the analog board pot.

According to the dead Mac scrolls, 1170n controls horizontal deflection and when it fails you get nothing but a flat bright horizontal line.

That’s why I swapped analog boards. But the new one can’t be adjusted horizontally for some reason.

 

[jonschultz]

I see, but a bright, horizontal line means that vertical deflection has failed. Horizontal deflection is still working just fine in that case. Failure of horizontal deflection almost always results in absolutely nothing on the CRT functioning because a lot of the circuitry depends on the flyback being driven by the horizontal deflection.

 

[iantm]

oooh. I’m mixing up axes then. Either way the dead Mac scrolls pointed to this particular chip when it’s a horizontal line. Hoping replacing it fixes that.