EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: necroscope on October 20, 2012, 01:05:03 am
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Ok since getting my first scope last week A rigol DS1102E,
I have what may seem a very silly question,most of my test gear for pcb's and ic's like comparator/logic probe and an old 80's bk precision in-curcuit ic tester require the the pcb to be powered on to perform a test, now i have noticed that the ic's still give a signal to the scope even with the power switched off, Why is this?
and when checking digital ic's whilst powered on especially some 256k rams on modern boards the 100mhz scope seems to max out the bandwidth settings without being able to get a decent visible waveform is this because a 100mhz just doesnt cut it or would i be doing something wrong the boards in question are running occilators of around 13,333mhz for logic and 3.57 for audio,The scope seems to work fine for 80's pcb's but i am having troubles once playing with the mid to late 90's gear.
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My best guess is that the signal it's picking up is EMI from the power lines, etc. Touch the probe with your fingertip and you should get a huge response. The 'scope is a hell of a lot more sensitive than your logic probe.
Not too sure about the second problem. Can you elaborate a bit?
Oh, and not to be rude, but can you please try to use separate, complete sentences? I did my best to figure out your post and help, but it was pretty hard to read.
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Sorry about that i seperated the questions.
In regards to the second question,I guess it may have to do with the auto button on the scope but when i try and aqquire a signal off of a 90's era pcb then i have difficuly in tuning the signal in to get a large image on the screen that i can see clearly before the scope says max/power or time Div,
And if i use the auto feature to find the signal it will come up on screen with max bandwidth and the waveform looks no bigger than a fat line with a few blocks sticking out of it,
Does this mean i need alarger bandwith to view these waveforms properly or would it be because i do not know how to use the scope correctly yet?
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Sounds like you need to learn about triggering. Forget that auto button exists. Watch at least the first several videos by w2aew in this thread.
https://www.eevblog.com/forum/beginners/oscilloscope-training-class-(long)/msg50100/#msg50100 (https://www.eevblog.com/forum/beginners/oscilloscope-training-class-(long)/msg50100/#msg50100)
Or go to his YT channel https://www.youtube.com/w2aew (https://www.youtube.com/w2aew)
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i try and aqquire a signal off of a 90's era pcb
Does this mean i need alarger bandwith to view these waveforms properly or would it be because i do not know how to use the scope correctly yet?
the 1102 (even the modded 1052) has no trouble probing 200MHz except a bit attenuated. what you need is to give more info about your question, such as pictures? or circuit or voltage level you are probing? is the BW limit for the channel turned on? if yes, turn it off.