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My SE was working fine until I took it apart to clean it, and after reassembly the tube won't turn on, what could cause this? enter link description here

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    I assuming you are familiar with electronics and specifically CRT's. Be careful around that CRT voltage - it can kill you dead as a door nail. – Geo... Oct 6 at 17:46
  • The video loaded too slow to view - can you describe what happens? Is there an orange glow inside the tube neck? Any sign of EHT (eg. crackling at turn on/off)? – Bruce Abbott Oct 7 at 6:52
  • The orange glow is barely visible in daylight. Should be checked when it's dark around. From the video it seems that all connections to the tube have been properly reapplied. Did you check the brightness control knob? Maybe it's just set too dark. – PoC Oct 7 at 8:10
  • @Geo... The residue EHT from B&W CRTs cannot kill a healthy human being. The inner and outer coating in the tube form a capacitor of a few nF, charged to the EHT of about 16 kV (and getting less over hours). This equates to just a few joule of energy. Touching the EHT connection knob at the tube cone and also the outer coating will hurt badly and teach anyone a lesson (to use two screwdrivers crossed to discharge this cap before handling the tube). – PoC Oct 7 at 8:18
  • @PoC Bingo it was the brightness control – yanagibashi Oct 7 at 23:13
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Without any other information, my first likely response has to be for you to verify the reassembly. Since I don't know what you actually took apart/disconnected, any errors made putting it back the way it started need to be eliminated first.

If I assume that you did a minimal disassembly of the internals, or have verified everything is back in its proper place (and connected properly and with proper polarity, etc.), then the next thing to check should be the most common causes of a blank screen on compact Macs.

From my experience, the most common cause of this symptom for a previously working machine is a cracked solder joint on the analog board. One of the "features" of these machines was they have good convective cooling because heat generated at the bottom of the machine is allowed to rise and escape through the top, like the cute little chimney that is the original Mac. This subjects the analog board on the left side of the machine to thermal gradients and after so many cycles the solder joints tend to crack from the extra strain, and this can disrupt the video signals.

I've fixed several machines by going over the solder side of the analog board with a magnifying glass to identify any suspect looking joints and reflowing them. You can easily do this with just the case removed and moving the white mylar (or cardboard) sheet that covers the solder side out of your way.

  • Cracked solder joints on the SE and SE/30 (identical analog boards) happen most likely at the connector to the deflection yoke. So one can see a very bright horizontal or vertical line which is sensitive to slapping at the case. – PoC Oct 7 at 8:32
  • This was helpful but it turns out I'm just an idiot and the brightness was set too low – yanagibashi Oct 7 at 23:14

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