Tektronix terminals

Rick Bensene rickb at bensene.com
Sun Feb 11 10:22:10 CST 2007


Christian wrote:

>Another unrelated question: The 4010 I got needs an awfully long time 
>until it will fully erase the screen (at least 20 minutes). When it's
cold 
>it will only erase the center in the shape of a (distorted) circle, the

>corners won't be erased. Is this a typical sign of a used CRT? I know
the 
>main heater and cathode (for the writing beam) are fine, I suspect the 
>collimation electrodes or the flood gun. Does anyone have experiences
with 
>that problem, is there any cure (e.g. a longer flooding time) ?

I used a lot of 4010s and 4014s in my days at Tektronix, and saw this
type of problem on numerous occasions.  The primary terminals for the
Control Data Cyber 73 (and later, an added Cyber 175), and Vax 11/780
(VMS during the day, BSD 4.x Unix at night (for the hacks to play with),
intermittently) were 4010s and 4014s.  There were user areas with a
bunch of these terminals grouped together.  These user area terminals
were very heavily used.  Most people didn't have terminals at their desk
in those days. The flood system that erases the screen has a limited
lifetime.  I know there was some adjustment inside both of the terminals
(but you'd need a service manual...perhaps bitsavers?) that would adjust
the flood current.
However, if adjusting this didn't work, they'd check a couple of test
points on one of the circuit boards, and if all the numbers came back
right, the factory service guys would not fuss with it anymore, and
start right away on replacing the tube.   A good factory service person
could replace the tube in a 4010 (took longer for a 4014) in about 20
minutes.

My guess would be that, given the many, many years this terminal has
been around, that the tube is just plain worn out.  It is a possibility
that some of the components in the flood drive circuitry have changed
characteristics over the many years...resistors and capacitors can do
this, as well as active components due to heat and power cycling.  I'm
sure that there's service documentation or schematics online somewhere.
If bitsavers doesn't have it, I know that there is a website dedicated
to Tektronix equipment, and has scans of lots of manuals and such, but
can't recall the URL (don't have it bookmarked).  Such material would at
least let you know if the tube is tired, or if perhaps something else in
the flood drive circuitry has gone astray that might be repairable.

Rick Bensene
The Old Calculator Web Museum
http://oldcalculatormuseum.com







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