Test Equipment: Oscillocopes

[MileHigh]

Well I hope the scope is on X-Y but I am highly suspicious.   You have a dot in the center and you can see two pale filament curves going towards the bottom of the screen.  I am suspecting that perhaps the the scope is not on X-Y and the horizontal timebase is not working.  The explanation for the two pale filament curves is that normally the beam is pulled off the screen below the bottom of the display during the horizontal flyback.  If this is the case, as the timebase knob is switched to lower speeds you might see the two pale filament curves start to flicker.

If we assume that I am correct and there is no timebase sweep, and you see varying flickering speeds when you change the timebase, then that would be telling you that the horizontal timebase oscillator is most likely still working.  I think there is a good chance that it could then just be a mechanical contact problem somewhere inside the scope.  The next step would be to try whacking the side of the scope just like an old TV.  Do this very lightly at first and do not do it hard and do it at your own risk.  Try a light whack for different timebase settings.  If after a whack you see the beam do a normal horizontal deflection, even it it is just for a fraction of a second, then stop whacking and you are 90% of the way towards the solution.

The whacking made a failed electrical contact between the horizontal timebase oscillator and the horizontal deflection amplifier connect for a short time.  So then the next step would be to open up the scope and clean all of the contacts associated with the rotary timebase selector switch with Q-tips and WD40.

Here is a "big secret:"  Just put a very tiny tiny amount of WD40 on each contact point, then cover the opened up scope with something to prevent dust coming in and then just wait about two days.  The WD40 will do it's magic over the two days.

I learned this from this guy's channel:  https://www.youtube.com/user/AllAmericanFiveRadio

I have watched clips were he does just that.  Takes a tiny tiny amount of WD40, applies it to the bad contacts, waits two days, and then everything works fine.  When you do this instead of spraying you do not contaminate the inside of the scope with excess contact cleaner.

CAREFUL if you take my advice and whack the side of your scope.  Perhaps opening up the scope and just tapping on the rotary switch for the timebase selector with a piece of wood would be better.   All of my suggestions and advice are at your own risk.

MileHigh

P.S.:  Whenever you see a static dot on your scope display you should immediately turn the intensity way way down to protect the screen phosphor.

[TinselKoala]

Please read the SM from the link above about cleaning the switches and other contacts.  Sorry, but the SM specifically warns against things like Q-tips (they leave fibers behind which can cause intermittent contacts) and petroleum based solutions (they degrade certain circuit board materials used in the scope.)

I do agree with the gentle whacking, and the rest of the stuff in your post. The behavior of the scope has changed since Brian has cleaned it, so it's almost certain that he's managed to knock something loose,  disconnected or broken a wire,  or fouled a switch contact or something like that.

The first thing, though, is to get it out of X-Y mode if that's where it is, and see if any kind of trace makes sense. The fact that the display has the really bright spot on it is a little disconcerting, I don't know if the Intensity control is fouled or what.  I think at this point that there definitely is a problem inside, but also that the controls aren't set properly to produce an interpretable trace.

[MileHigh]

No Q-tips makes sense.  In that guy's channel that I linked to, he may have just put a tiny tiny drop of WD40 on the dirty contacts with the tip of a needle or a jeweler's screwdriver, and then he just touches the contact point.  When I saw that I was somewhat surprised and embarrassed because I have cleaned the pots in old 1970s amplifiers with very messy "brute force spraying."   

That's a great segue into some classic advice:  You want a good sound system for your main computer?   In the springtime go out to some garage sales and get a nice 1970s integrated amplifier or stereo receiver for $30 or less.  Clean the volume control knob and the input selector switch.  Get a decent set of stereo speakers and then you will be in computer sound system heaven.   It's getting pretty late now, so old amplifiers and receivers are probably getting scarce!

[Brian516]

AHA!! we have liftoff!!   still some kinks to work out it seems, but progress! 

I don't know if it was just be being dumb and not having the proper settings, but the only real difference between the settings before and the settings now is the coupling is set to AC instead of DC, and the input is also set to AC. oh, and the time/div to 1ms instead of X-Y... which must have been the major issue I suppose??
I did change the coupling to AC and input to AC before when I was trying to get it working, but not the time/div.  If not, maybe the gremlins inside the case fixed it while I was attempting to fix this 1000W amp unit.

One other thing that is different, which I mention in the vid, is where exactly I had the power plugged into.  before I had it plugged into an extension cord that also had a lamp plugged into it.  Now I have it plugged directly into the wall outlet, but it's the same outlet that I had the ext cord plugged into.

I'm going to go with the story that the tube gremlins fixed it....  so I don't feel so stupid! 
There are still a few kinks that those gremlins need to wrench on, though, such as the brightness of my vertical lines, the bad illumination bulb at the bottom of the CRT, and the pot noise.... haha

https://www.youtube.com/watch?v=M9slPe8A3lw

Thanks !!

[TinselKoala]

The video shows up as "private" so you have to put us on the list specifically by username. Or you could change it to "unlisted", then anyone with the URL can see it but it still won't appear on searches.

There is a difference between "Trigger coupling" and "input coupling". The input coupling is the one under the channel vertical scale knob. The Trigger coupling is over on the right in the trigger/timebase section. Also the trigger source should "not" be set to "line".

There is still something wrong because even the X-Y display should not look like that; with no inputs to the channels it should produce a single dot, that can be finely focussed to a point, without tails or bright blooming.