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What's wrong with my oscilloscope?

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chris414

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Okay so i got given a *really* old oscilloscope (like seriously, from 1940-something) and at first i thought it was working perfectly. But then every so often the line on the screen gets really shaky and jumps around a lot, as if there's a dodgy connection somewhere (and persists for a good few minutes before returning to normal again). I bought another probe because I thought that there was just a bad connection in it, but that didn't solve the problem. I have yet to open the scope up and look inside, but I would imagine this is a fairly common problem and was wondering what the most likely causes of this would be that i can look for?
 

Sceadwian

Banned
Be careful if you open in to clean it out and take a look, you could jostle whatever's being 'flakey' into being simply broken.
 

tcmtech

Banned
Most Helpful Member
Could be a scratchy pot on the front. I have an old vacuum tube O-scope that does a similar thing and its from the control pots being dirty.
 

tcmtech

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Many Old O-scopes have never been opened and cleaned out since the day there were created! A good dusting can sometimes make all the difference!
 

Sceadwian

Banned
Just be careful. It's not common but let me tell you a nightmare story of mine.
My brother in law doesn't clean his machines out at all and he was having trouble with one of them, so I came over and there was dust inside so thick it was completely matted into an almost cloth like substance. I carefully tried to clear out as much as possible, starting it up afterwards the power supply dead shorted and the smoke came out =) I'm guessing during cleaning a piece of it got jamed in the high voltage section of the power supply and it fried when it powered up.

I have a scope almost as old as me as well, it's a little flakey, turning it off and back on cleans up the trace when it's skippering about and the pots are a little flakey sometimes usually from sitting in the same position, running them back and forth from each detent a few dozen times tends to help smooth out any dust on the pot's or anything.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I carefully tried to clear out as much as possible, starting it up afterwards the power supply dead shorted and the smoke came out =) I'm guessing during cleaning a piece of it got jamed in the high voltage section of the power supply and it fried when it powered up.
I would agree, it's EXTREMELY unlikely that dust causes any problems, and you're far more likely to cause a fault by cleaning it out.

If you do want to make the effort, use a vacuum cleaner and a soft paint brush - hold the nozzle near the board, and gently brush with the paint brush.
 

Sceadwian

Banned
My situation was a bit abnormal, I don't what it was about the air at his place just the right moisture and dirt content (2 kids 2 adults 3 cats) it formed a dense cotton like substance. His last PC just died the CPU from over heating or a bad motherboard because a solid blocking blanket had formed over the heatsink fins. Makes TCM's basement look clean, but only inside the PC's.
 

unclejed613

Well-Known Member
Most Helpful Member
my experience with old oscopes is, vacuum it out, don't blow the dust out, and pull the tubes one at a time and put them back in. tube sockets can get oxidized and cause problems like what you're describing. if the dust contains carbon particles, like soot, it can cause shorts if you try to blow the dust out. that's less likely if you vacuum it out
 
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