68kMLA Classic Interface
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| Mac SE retrace lines, faint normal image | |
| Posted by: SpocksBeer on 2025-02-10 17:43:21 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! | |
| Posted by: jmacz on 2025-02-10 21:25:06 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. | |
| Posted by: zigzagjoe on 2025-02-10 22:04:43 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. | |
Posted by: SpocksBeer on 2025-02-10 23:37:55The 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. | |
Posted by: SpocksBeer on 2025-02-10 23:38:55You 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. | |
| Posted by: SpocksBeer on 2025-02-11 02:42:03 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  | |
| Posted by: zigzagjoe on 2025-02-11 05:32:05 Fantastic. Glad that sorted it for you 🙂 | |
| Posted by: obsolete on 2026-03-28 16:47:52 Great info, thank you @zigzagjoe. This one's not in The Dead Mac Scrolls. I repaired an SE/30 neck board that suffered the same fate as @SpocksBeer, and the system displayed exactly this failure mode. New 2N3904 at Q1 and it's as good as new. I only wish I'd found this thread sooner, before I'd swapped every other part in the system besides the neck board 🙄 | |
| Posted by: SpocksBeer on 2026-03-30 16:14:54 Nice one @obsolete I've just landed another odd one, an SE/30 where the R1 resistor on the neckboard (big 3w 1kOhm guy) gets super hot when powered on. Symptoms of this one are a very dim image, messed up possibly with retrace lines (I don't run it long enough to really get a good look). Hoping it's the Q1 transistor again, but with a different failure mode (like failing short). Will investigate and report back for future search engine value! | |
| Posted by: SpocksBeer on 2026-04-01 20:54:48 Narrator: it wasn't Q1. Started another thread 🙂 | |
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