I recently rescued two oscilloscopes from being scrapped at work. They are BK Precision 2120Cs, both of which have display problems. They were likely bought around the same time and have been used by the calibration group, which really doesn't change the settings very often, if ever. For the most part I'm willing to bet the only control they ever touched was the power button.
These scopes are probably left on all day every day and only turned off when the work day ends. The scopes have the following problems:
Scope #1:
The first scope I picked up reportedly had no trace. However, when I brought it home and powered it up a trace did eventually appear, though it took a while and was extremely dim:
I opened up the case and performed the sniff test and a visual inspection, but I cannot seem to find anything out of place. I did notice that the coil wound around the tube was loose and I re-secured it with epoxy, but that did not seem to make any difference. I fiddled with the intensity knob and trimmer pot but could not seem to make the trace any brighter - only dimmer. The other controls appear to work as expected - just the trace is dim, and that's the case for both channels.
Scope #2:
The second scope I picked up had a nice bright trace, but its behavior was a bit funky. When I first powered it up it seemed to work just fine, with the exception of a little burning on the left hand side of the screen (the image makes it look worse than it really is). However, after letting it sit for a few seconds eventually the trace became very wide (1/4-3/8 inch or so?) and would not respond to the intensity control. It was also difficult to tell whether or not the focus control was making any difference.
After initial power-up:
After a few seconds:
The trace would come in and out - sometimes it would be clean and focused, sometimes it would get thick and blotchy again.
Does anyone have any ideas of what might be up with these scopes? Again, being that they were probably purchased around the same time and used for roughly the same purpose for the same number of years, I wouldn't be surprised if the problems were related and possibly a known issue with these scopes....?
Thanks