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.

 

[Mark_W]

Horizontal width is controlled by the width coil, not potentiometer.

I assume you are talking about the vertical height of the image, in that case clean the height adjustment potentiometer with contact cleaner, make sure it's not damaged and is actually turning, you should see the wiper arm rotating from the component side of the analog board when you turn it. There are only 2 components in the height adjustment circuit iirc, so should be easy to identify the cause.

Also for the other board with horizontal line, reflow the yoke connector first if you haven't done so. Also when swapping analog boards I always swap the yoke with it, since all adjustments are specific to the yoke it paired with originally.

Btw you can find replacements on aliexpress for like $1 each, bought a lot before and haven't got any issue, but keep in mind many chips on aliexpress are used/recycled

 

[iantm]

I think the two problems have been a mixed up a bit. But yeah: one board either needs the deflector chip (tda1170n) replaced or the yoke reflowed because the raster has collapsed to a horizontal line.
The working analog board might need to be retuned, as I have no idea which board pairs with which yoke.
Hopefully I can adjust the width coil on that one. The height, brightness and focus work fine on that board. I have to figure out why I can’t adjust the width.