Test Equipment: Oscillocopes

[MileHigh]

It certainly is strange.  It possible it's related to the flyback blanking interval again but that's just a guess.  If the trigger level is set just at the upper or lower threshold of the square wave that might cause some horizontal jitter if you are right at the edge.  However, that can't explain the loopy "noise" waveform.  You should try changing the trigger level just the same and then leave it at around zero volts.

Something is loopy for sure.  For me the next step would be to exercise every single function of the scope for the internal square wave and for an external signal to get a full sense of the scope's health.  However I realize that would be next to impossible for you because you are a newbie.

The "noise" waveform is exponential in nature.  That's not a surprise in itself but it might be a clue.

TK mentioned thermal issues also.  The advice from me would be to chill the scope down just a bit (you don't want condensation) and then run it and see if the scope works fine for 10 minutes before the problem starts happening.  Then like TK said you may have a single failed semiconductor component.  Finding that is not too difficult if you know what you are doing.  I would not advise you to do this yourself.

[MarkE]

https://www.youtube.com/watch?v=C8WUWgIVG0A

says it will be done uploading in about 6 minutes.
Hopefully it's just some noise off the input.  It wasn't there before, though.


AHHH!  Now it's all just getting worse!!  I have a curved line on the screen when there is no input into it, and that noise wont go away. I tried different clip leads, different wire into the input jack, and even a probe.       I hate my life sometimes....

Your brightness is set way too high.  Youare going to burn the screen with settings like that.  Put the same signal on channel B and see what you see.

[TinselKoala]

Heck, I think Brian can handle it. The tantalum caps are easy to recognize on the boards, and simple to test by unsoldering one leg and testing for resistance with the DMM, or a capacitance meter that he could probably borrow if he doesn't want to buy one. Check the PS voltages in the low voltage supplies at the test points indicated on the schematic with a DMM, following the troubleshooting chart in the SM for the power supplies. I'll bet a cheezburger that there is an off-voltage supply and that the cause is a bad tantalum or foil electrolytic capacitor or two.

[Brian516]

I have a few things I have to get done today, but hopefully later this evening I'll be able to do some more troubleshooting, test channel 2, and run thru the tests you both suggested while recording it all on vid.  it would be nice if I had an actual vid cam and tripod for this but I'll see if I can borrow an extra set of hands for a few min so I can get it done quicker. 

You sure using a refrigerant chill spray in something like this won't cause any additional problems?? what am I saying, of course you are,  you must be.. you know a whole lot more about this than I do.....

I was thinking about possibly opening it back up and finishing the cleaning by removing the trigger boards so I can access the time/div drum and finger contacts properly, and clean it all up really good with IPA.... just in case there is some sort of fuzz in there crossing some contacts, and so we can get an entirely accurate picture of what could be wrong while knowing it isn't a switch contact or dust issue.  then I could leave the case off for the testing to get a visual with power on, and also check the voltages.  do you think this is worth doing first, or should I just leave it as-is and continue troubleshooting?

[Brian516]

Your brightness is set way too high.  Youare going to burn the screen with settings like that.  Put the same signal on channel B and see what you see.

that is an effect of the camera.  the brightness was only up just high enough to where the vertical traces are slightly visible.  the illumination was also down all the way.  I don't know why the camera does that.  maybe I have it on low light setting or something.