> I realize that this subject undoubtedly has come up before but, since
> we are on the topic of fixing SE/30 CRTs I wonder if anyone could give
> me some advice on how to fix an issue I have with my SE/30. When I
> turn the computer on the screen shakes, not unusably yet annoyingly.
> It seems to shake most when the machine is first turned on, but lessens
> as the computer warms. It may however return after the computer has
> been on for a while. I suspect that I have some problem with my analog
> board, perhaps a leaky capacitor or perhaps it is having a problem
> getting a steady current from my power supply. Does anyone have a
> better explanation perhaps?
There are a few common sources of this problem, roughly in order of frequency of
occurrence, starting with the most likely and working down from there:
1) Bad solder joints: The four-wire crt yoke connector is particularly susceptible.
Follow the (there's only one) 4-wire connector from the crt yoke to the analog board.
Carefully (to avoid the hiss of death) unplug the connector and inspect
the pins on both connector halves. If there's a flaky joint, it often produces
overheating that seriously tarnishes one or more contacts (in extreme cases, the
connector housing even melts). If you see this, the only reliable fix is
replacement of the connector (a bit of pain and expense), or merely hardwiring around
the connector (ugly, but simple and reliable).
Reconnect the connector. Even if you didn't see a problem, resolder (with fresh
solder; don't merely reheat) all four pins on the foil side of the analog board.
Often, the problem is a hairline crack that may be nigh impossible to see, and
this operation will fix it. Don't solder without the connector hooked back up,
otherwise the heat may cause distortion of the connector shape, and you'll have a
tough time reconnecting things later.
Those aren't the only solder joints that could cause the trouble, but they're the most
likely ones.
2) Bad coupling capacitor: You didn't specify if the shaking was primarily in one
direction or another, but I'm betting it is in the horizontal direction. If so,
another likely candidate is a large *nonpolar* capacitor (usually 3.9uF or 4.7uF)
in series with the horizontal winding of the yoke. It's on the analog board, often
secured to it with a mound of hot glue (don't mistake it for capacitor guts). You can
usually see if there's bulging at the top or bottom of the capacitor. If
so, replace it. If you have trouble finding the capacitor, feel free to take four or
five 1uF ceramic capacitors (50V is a good choice) and wire them in parallel. This
combination is actually electrically superior to the original electrolytic.
3) If the shakiness is both horizontal and vertical, then the high-voltage ("flyback")
transformer may be the problem. Nothing you can do in that case but to replace it.
However, just as with the yoke connections, the solder joints sometimes
degrade over time, and so it doesn't hurt to resolder all of those, too, while you're
in there.
4) Power supply instability: I've never seen this as a source of shakiness, but it's a
possible cause. You can't test for this with a voltmeter, as suggested by somebody,
though. A typical voltmeter responds so slowly that it will report only
an average value, so you won't see short-term voltage instability. You'd need an
oscilloscope. But even after looking at it with a scope, you'd probably still do what
you would have done without one anyway: Unplug all connectors, reseat them,
then hope for the best. :-)
Good luck!
--Cheers,
Tom
--
Prof. Thomas H. Lee
Center for Integrated Systems, CIS-205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu
650-725-3709 voice, -3383 fax
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