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Old Oscilloscope

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large_ghostman

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I have a Old oscilloscope that has never really worked, its pretty crappy and i cant read the name on it. The bandwidth is low, I cant remember off hand but its around 2 or 10Mghz, I would like to fix it as I am building a component tester, so would be great to use that scope for it, that way I can leave it semi permanent connected.
The problems are probably many but its a basic machine and old, so shouldn't be too complicated, also its purely analogue, the main problem is the dot is a splodge! no definition to it, you can tweak all you like but it dosnt change, also when I put a signal in nothing happens, it does however sweep across the screen, so what section should I look at first? and is it likely I will have to mess with the tube and the very High voltage stuff?? (answer no to last question ;) )
 
Not a lot of info there LG, my crystal ball is failing.

I suggest for a start that you check all the supply voltages (difficult when you dont know what they should be), and that includes the BIG ZIGGIES, mind your fingers!

JimB
 
is it likely I will have to mess with the tube and the very High voltage stuff?? (answer no to last question ;) )
No you would get a faded dot or no dot if the HV was falling.
Because its a blob I would say the focus needs to be adjusted.
Look up CRT focus adjustment to give you an idea.
 
Faded is almost a description of it :(, sorry lack of information, I dont have it handy. I will give as much information as I can tomorrow. I am thinking input circuit might be iffy, but that should be simple on this scope, I very much doubt there are ASICS to worry about or special chips.
 
Hiya LG--

I had a scope from the '70s that had a similar problem. There was just a big green blob on the screen. While some photos of your scope would be very helpful, I can tell you that the problem I had with mine was a blown (and I mean BLOWN) capacitor on the timebase board. The entire area was corroded, but after cleaning it up, laying new traces, and replacing the capacitor it worked good as new. Some images of the front end of the scope (the screen) would be helpful, as would be photos of the inside. Do you know approximately what decade it's from? That would help us determine whether it might be (for example) a tube, a capacitor, or an IC.
 
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I would say roughly 70's or maybe 80's its hard to tell, I am waiting for dad to bring camera home from his office, with luck will be tomorrow
 
Sounds good. Are you able to take it apart though? You can always do a visual inspection to see if there are any obvious issues (this, of course, is only to be done if you have tried adjusting the focus and everything first and it didn't work). For example, when I opened my scope (after tweaking the knobs and everything to make sure it wasn't a problem with the settings) I caught a very string whiff of burnt electronics. That's your first sign that something is wrong with the components.

However, being from the '70s or '80s means it is a CRT, and that there are high voltages present. If you do open it up, don't touch anything. There could still be a nasty charge stored there. You should still be able to look over the boards and smell them.

Regards,
Matt
 
thanks for the link :D most useful!
 
Check all of the electrolytic capacitors. Caps that old are bound to be bad in ESR, leakage, value. For that matter get a newer scope on eBay instead. They are plentiful and good ones sell for very low prices if you are diligent in looking and patient for a good deal to come along.
 
Oscopes not so cheap in uk! I have seen loads on ebay in the states that are cheap, but by the time you pay postage and customs fee's (most wont post as a gift or lie about value), then you havnt saved a thing!
and it kind of defeats the object, I wont to get this one working because its crap and old, so would be perfect for my component tester project :D
 
I have repaired 'scopes from the 70's for people, the favorite is high resistance switch contacts and as mentioned electrolytics.
Buy yourself a can of servisol 10, unless you allready have one and douse the switches.
Telequipment liked using sockets for transistors, they have caused me trouble before, I just solder the trannys direct in the pcb, probably not 'best practice', but if it means you get wiggly lines instead of a shelf ornament so be it.
I had a philips that had a 'dot' half the size of the screen, that turned out to be a power supply cap.
 
What would you expect from a little ghost.
 
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