Mac SE retrace lines, faint normal image

[SpocksBeer]

Hi everyone,

I have an SE that came to me with a destroyed tube - the end of the neck had snapped off. It spent a little time powered on and arcing spectacularly before I'd realised what was wrong with the tube. After sourcing a replacement tube, it's now looking like this:



The machine boots normally, but the image is just so. Strong retrace lines, but if you look closely (in person) you can *just* make out a perfectly normal, albeit very low contrast, image of the desktop.

Before I get too deep into component level troubleshooting, has anyone seen this before?

Cheers!

 

[jmacz]

The analog board (left side of the Mac) should have an adjustable pot for brightness/cutoff, alongside the focus, width, height ones. Try turning that down. The service manual for the SE near the end should have more descriptions/pictures of the process.

 

[zigzagjoe]

You may have blown transistors on the neckboard. A fellow with one of my grayscale kits had a similar failure and I found the arcing had immediately destroyed several of the drive transistors on the NB.

 

[SpocksBeer]

The analog board (left side of the Mac) should have an adjustable pot for brightness/cutoff, alongside the focus, width, height ones. Try turning that down. The service manual for the SE near the end should have more descriptions/pictures of the process.

Thanks, forgot to mention that it responds normally to brightness controls (in that the image gets brighter and darker as it should), both via the front pot, and the sub-brightness adjustment on the AB, but the retrace lines do not change.

 

[SpocksBeer]

You may have blown transistors on the neckboard. A fellow with one of my grayscale kits had a similar failure and I found the arcing had immediately destroyed several of the drive transistors on the NB.

Thanks, I'll check that first. Would make sense that something on the neckboard got damaged due to the arcing.

 

[SpocksBeer]

And winner winner chicken dinner, it was the 2n3904 transistor on the neckboard. Now have a nice usable image (please ignore the tilt).

Thanks so much for the tip, zigzagjoe

 

[zigzagjoe]

Fantastic. Glad that sorted it for you