What's wrong with my oscilloscope? - Electronic Circuits Projects Diagrams Free

chris414 · 25th May 2009, 08:49 PM

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?

blueroomelectronics · 25th May 2009, 08:53 PM

Probably corrosion. Do you live near salt water?

Sceadwian · 25th May 2009, 09:02 PM

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 · 25th May 2009, 09:03 PM

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.

chris414 · 25th May 2009, 09:03 PM

hmmm... corroded where? so would you say don't open it at all?

tcmtech · 25th May 2009, 09:05 PM

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 · 25th May 2009, 09:26 PM

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** · 25th May 2009, 09:36 PM

Quote:

Originally Posted by Sceadwian

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 · 25th May 2009, 09:54 PM

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 · 25th May 2009, 10:35 PM

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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25th May 2009, 08:49 PM	#1
chris414	What's wrong with my oscilloscope? 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?

25th May 2009, 08:53 PM	#2
blueroomelectronics	Probably corrosion. Do you live near salt water? __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com/

25th May 2009, 09:02 PM	#3
Sceadwian	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. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."

25th May 2009, 09:03 PM	#4
tcmtech	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. __________________ "Issue a general safety warning. Then look the other way and allow stupidity the chance to eliminate itself." -- tcmtech "Those who can, Will. Those who can't, will achieve positions of power over those who can and then promptly stop them." -- tcmtech "Your impossibility may just be my day to day routine." -- tcmtech

25th May 2009, 09:05 PM	#6
tcmtech	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! __________________ "Issue a general safety warning. Then look the other way and allow stupidity the chance to eliminate itself." -- tcmtech "Those who can, Will. Those who can't, will achieve positions of power over those who can and then promptly stop them." -- tcmtech "Your impossibility may just be my day to day routine." -- tcmtech

25th May 2009, 09:26 PM	#7
Sceadwian	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. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."

25th May 2009, 09:54 PM	#9
Sceadwian	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. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."

25th May 2009, 10:35 PM	#10
unclejed613	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 __________________ .................................................. .................................................. . E=mc² (+/-1dB) "If a curl of smoke is seen, the technician will soon experience the cause of difficulty"........ CTX arcade game rgb monitor service manual 1985 DC-to-Daylight Blog (on this forum): http://www.electro-tech-online.com/blogs/unclejed613/