Further Tektronix 4014 debugging...
derschjo at gmail.com
Fri Apr 3 22:40:49 CDT 2015
So I may have been a bit premature in my declaration earlier this week
that letting the 4014 warm up for a few minutes solves the storage problems.
For the time being, I have it hooked up to a Linux box (so I can 'cat'
various files at it and stare in awe as it draws random things) and it
seems to be performing flawlessly; everything works (including the
discrete plot extensions). But I've noticed that over time as I clear
the screen that garbage starts accruing around the edges of the screen
-- only the middle gets properly erased.
At first power-on, the area that gets cleared is a circle maybe 10" in
diameter; this increases slowly over time and if I let it run for 15-20
minutes *most* of the screen gets cleared but there's always a bit on
the edges that remains.
I went through the portions of the alignment procedure outlined in the
service manual related to storage, and all voltages were within a
percentage point or two even after all these years, so not much required
There are two adjustments for the Collimation that control the size and
shape of the flood that erases the screen; the service manual suggests
adjusting these until the flood covers the screen. Adjusting the pots
all the way counter-clockwise causes the flood to get *slightly* larger
and cover more of the screen, but it's still not enough.
From reading the circuit description for the erase circuits (starting
on page 5-82 of the service manual), I note that the duration of the
flood (as controlled by the Collimation circuits) is controlled by an RC
network and I suppose it's possible that one or more of the capacitors
is out of spec -- but I don't know if the length of the flood has
anything at all to do with the area it covers -- can anyone shed some
light on this?
I suppose it's more likely that the tube's just showing its age. I
suppose I should be happy it works as well as it does.
At any rate, if anyone has any insight here, I'd love to learn more...
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