Was the focus properly adjusted? Did you played around with time/div to see if there is a signal on top of tsquare wave? If you ground the channel is the line slim?
Alexander.
Looks like a focus issue to me.
Pull out the "Trig View" button. This engages the bandwidth limiter. The scope may be picking up high-frequency noise.
The trace appears on a CRT because an electron beam is striking a phosphor coating on the inside of the tube. The amount of light emitted by the phosphor depends on the speed at which the beam is moving. The slower the beams moves, the more light that is emitted. Notice that as you turn the sweep speed up, the trace gets dimmer. So for a square wave, during the rising and falling edge, the beam is moving very very fast, therefore very little light will be emitted. It is normal and expected that a square wave will look like two separate broken/dashed lines on an analog scope.
With a grounded, flat trace, adjust the intensity so the beam is just easily visible in your ambient light conditions. Adjust the focus for sharpest trace. You will need to re-adjust the intensity if you change sweep speeds, but the focus should need little or no further adjustment.
Edit: @robrenz, yea same thing but you have numbers!
Edit @ModemHead, your post came in while I was posting this. Sorry but we are saying the same thing.
I am no expert but this may help you.
All you experts: I am intentionally simplifying some aspects of this description, don't crucify me.
This is the way an analog scope is supposed to behave. For a given intensity setting, trace brightness is roughly proportional to beam speed. On the horizontal portion of a trace the beam speed is equal to the horizontal sweep speed. But the approximately vertical portions of the trace the beam speed is a function of the volts per division setting and the rise time of the scope and signal.
That roughly vertical beam speed can easily be hundreds of thousands times faster than the horizontal speed. That is why the rising and falling edges are very faint or not visible at all.
Example: 1ms/div sweep speed equals 1cm/ms beam speed on the horizontal parts of the trace. apply a square wave with a 10ns rise and fall time (includes rise time of scope) and adjust v/div to have signal 1 division high. The beam speed on the rising and falling edges are 1cm/10ns or 100000cm/ms. 100000 times faster beam speed, no wonder it disappears
In general:
Adjust focus for the finest trace and leave it alone.
Adjust intensity for a comfortably visible trace on the sweep speed you are using and leave it alone.
Realize you are never going to get the rising and falling edges to be as bright as the horizontal part of the trace.
Brightnes related to time what beam activates phosphor is feature what they very hard try copycat also to digital oscolloscopes. In expensive high-end digital oscilloscopes it works well but not still ads good as in analog. But also this is disadvantage in analog when need capture fast things. If people have lot of experience with analog osciloscope he can use this brightness differencies also as information. This feature have pros and cons. With very fast single shot things more just cons. But with repetitive signals it may also give big advantage over entry-level or middle level digital oscilloscope.
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Focus.
Use sinewave. Around 6 div high and speed so that cycle is 2 or 3 divs.
Then adjust brightness so that it is not dim and not too bright!
Then adjust together focus and astic (in front panel) for best overall sharpness. (focus and astic affect different direction of focus)
This need be well focused in x and y axis. Also you can use square but there is problem due to risetime and top and bottom is easy too bright and edges barely visible or you need adjust brightnes too bright. For Focus/astic together adjustmet it is better use sine so that signal brightness is nearly same every place.
I do not remember if in this model is also separate "focus" for highest brightness or other compensation.
Also you can easy find full service manual and there is full detailed paragraph about adjustments. Follow it in order.
There is also exact procedure for display (service) adjustments. All display related adjustments need be adjusted and values measured as service manual tell. Tektronix service manuals are very good and every word need take serious, also there are things what need do in order stated in manual.
Basically it looks in pictures like there is not bad problem.
Here you find service manual: http://bama.edebris.com/download/tek/465(2)/465.pdf
Paragraph 6 start with power supply check but adjust ONLY in extremely need becouse it affects to many things.
Look table 6-1 about adjustment interactions.
Then display and z-axis. Do not go inside adjustments if you have not experience and knowledge about High Voltage working. There you need example measure and adjust over 2kV .
For best focus - astic adjustment you can also use X-Y mode and dim dot (not too bright!) near center screen. Adjust both together for best dot.
Has anyone mentioned CRT aging? That is always a fear when buying any old scopes.
Specially ageing maybe problem if tube is used very special way (and tube is also littlebit "special"). Some kind of example is HP8568 spectrum and other similar or nearly similar. There is one beam and it is used for drawing all. Signal trace of course and also then data txt etc but then also scale lines. It need large dynamic becouse different things draw with different speed and different current. (driving circuits are extremely complex) After tube have extremely high power on hours there can see problem so that thin scale lines, txt and sweeped trace can not focus together. There is special way to stretch lifetime but it need special knowledge and skills to do it. I do not know power on hours where this problem come clearly visible so that inside service adjustments can not anymore help. Tube dynamic change. Overrall these very expensive special tubes are very good.
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3n2323, I have the same scope... and this is just the way things are.
as someone alluded to earlier, its the amount of time that the electron beam dwells on that particular spot on the phosphorescent screen. when viewing a sine wave it looks nice and continuous because its a steady rate at which the beam moves. on a square wave the beam has to jump VERY rapidly in the Y direction, so the time it is able to dwell on a particular point on the screen is minimal. Hence the dimmer appearance of the waveform on the vertical axis. Generally I adjust it such that the horizontal portions are at a "comfortable" setting for me, and ignore the vertical lines because I know they are there anyway!
There are two things that can affect the scope trace if it is out of focus.. first is "FOCUS" and the other is a small pot called "ASTIG" (adjusted with a non conducting screwdriver) short for astigmatism. ASTIG helps adjust the beam to compensate for the shape of the screen, once set, you generally dont touch it again until you notice a beam that is sharper in the center than it is on the sides. After this adjustment "FOCUS" sharpens or blurs the entire image and is the only one you touch on a daily basis.