Display "Blooming" and "Buckling"?

[CC_333]

Hi,

I have an SE/30 which seems to be experiencing some oddness in the display. At the corners, everything seems to bend in toward the center, which distorts the menubar on top (the bottom isn't noticeably affected, probably because there isn't really anything there except the desktop pattern). Also, the distortion worsens if I turn the brightness up, and the display expands considerably.

I was wondering if there's a reason why this may happen, and what it would take to fix it. I doubt very much this is normal.

Other than that, the display is nice and bright and clear.

My thoughts so far:

1. Voltage issues (possible P/S issue)
   
2. Analog board component level failure (such as a capacitor or ten)

Thank you,

c

 

[trag]

I think it could be either one of those. At the greatest deflection (corners of the screen), the magnets in the yoke are at their highest voltages, in order to change the direction of the stream of electrons the greatest amount. If the high voltage isn't available, then the deflection coils can't supply sufficient voltage to deflect the electrons all the way out to the corners.

I think, but am not certain, that this could be caused either by low supply voltage or by defects in the components on the analog board that process the power before it goes to the yoke.

 

[CC_333]

I think, but am not certain, that this could be caused either by low supply voltage or by defects in the components on the analog board that process the power before it goes to the yoke.

Then, perhaps, I will try readjusting the power supply voltage. Mac Repair & Upgrade Secrets (hereafter MRU&S) says that the SE power supply is auto-adjusting, although there is a voltage pot for manual override.
I'll try that and see what happens (I don't think it'll blow anything up!)

If that doesn't work, then I'll have to look at testing and replacing any components whose impending failure could show this as an early symptom.

c

 

[CC_333]

Hi,

I adjusted the voltage (and the screen brightened up a bit, so maybe there was some under voltage going on), however, it didn't affect the distortions in the display.

I don't know if it's me or not, but I think it did make it a bit sharper though.

I guess I have to fix the analog board. The capacitors look OK, but they're most likely getting old, and it's conceivable that failing capacitors can cause weird things to happen in the display.

Recap time!

c

 

[nvdeynde]

The distortion has to do with misaligment of the magnents around the coil of the yoke. You'll have to fiddle with them to get the picture right but it's best to mark the original position of each one before you start turning them. Be carefull for the high voltage !!

If it's impossible to get the display right after fiddling with the magnets, then there's probably a small short somewhere in the wires of the coil that messes up the display. Then the only option is to replace the Yoke coil.