Are these things I should consider bad

[TinCanAlley]

Originally Posted by N2IXK

But some scopes can automatically detect the probe setting, and adjust the vertical scale range to reflect the probe attenuation and prevent confusion. This requires both a scope and a probe that support this feature. Do yours?

If your scope is doing this, then the scale really is 5 volts/division. If your scope or your probe doesn't do this for you, then the scale is actually 50 volts/division. This makes all the difference in the world when trying to interpret the waveforms as ripple on a power supply rail.

I have a Tektronix 465M. No auto settings for the probe.

I've been thinking about the waveform. It's a 240V source, so the 5V/Div would be too low to show it and the 10x probe would make it 50V/Div and it would cover almost 5 divisions. What I got was way under that. I'm going to use the DMM to go all the way back to the boost diode and when I find the point it's 240V, I'm going to scope it. With a setting of 5V/Div and the probe in 10x, I should get a form that covers over 4 divisions, right?

[N2IXK]

Originally Posted by TinCanAlley

I have a Tektronix 465M. No auto settings for the probe.

I've been thinking about the waveform. It's a 240V source, so the 5V/Div would be too low to show it and the 10x probe would make it 50V/Div and it would cover almost 5 divisions. What I got was way under that. I'm going to use the DMM to go all the way back to the boost diode and when I find the point it's 240V, I'm going to scope it. With a setting of 5V/Div and the probe in 10x, I should get a form that covers over 4 divisions, right?

Where is your baseline set? Are you operating the scope AC or DC coupled?

Typically, for checking ripple on a power supply, you would operate AC coupled, so you only see the AC component of the signal, and ignore the DC. If you are running DC coupled, the baseline should rise a bit less than 5 divisions (250V) from zero, with ripple superimposed on it. You can do a quick sanity check with a DMM, by measuring the 240V supply twice, both in DCV range (should show ~240V), and in ACV (should show close to zero if no significant ripple is present).

From what you are telling us (5 V/div with a 10:1 probe and no auto priobe ranging), the scope is actually showing you 50V per division, or a waveform of ~75 Vpp. This is WAY too much noise on a supply rail, and would easily explain the jailbars.

You really need to learn how to use a scope effectively in order to get useful information from it. Take a couple hours and watch this GREAT YouTube training session:

http://www.youtube.com/watch?v=8ZKMrzTGxLQ

[TinCanAlley]

Originally Posted by N2IXK

Where is your baseline set? Are you operating the scope AC or DC coupled?

Typically, for checking ripple on a power supply, you would operate AC coupled, so you only see the AC component of the signal, and ignore the DC. If you are running DC coupled, the baseline should rise a bit less than 5 divisions (250V) from zero, with ripple superimposed on it. You can do a quick sanity check with a DMM, by measuring the 240V supply twice, both in DCV range (should show ~240V), and in ACV (should show close to zero if no significant ripple is present).

From what you are telling us (5 V/div with a 10:1 probe and no auto priobe ranging), the scope is actually showing you 50V per division, or a waveform of ~75 Vpp. This is WAY too much noise on a supply rail, and would easily explain the jailbars.

You really need to learn how to use a scope effectively in order to get useful information from it. Take a couple hours and watch this GREAT YouTube training session:

http://www.youtube.com/watch?v=8ZKMrzTGxLQ

Gonna get some popcorn and watch that video.

Okay, just did a scope of the 240V line just after it comes off of the resistor into the main feed (where the capacitor is and the where the 240V gets distributed). I had the scope set to AC coupling, V/D set at .5, the T/D set to 20us and probe at 1x. The rippled waveform covered 1.75 divisions peak to peak. So that would make the AC less than a volt, correct?

[N2IXK]

.5 V/div and a 10:1 probe is 5 V/div. A signal 1.75 divisions high would be 1.75 x 5, or 8.75 Vpp.

[TinCanAlley]

Originally Posted by N2IXK

.5 V/div and a 10:1 probe is 5 V/div. A signal 1.75 divisions high would be 1.75 x 5, or 8.75 Vpp.

Sorry, forgot to mention it was in 1x setting on the probe.

[andy]

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[TinCanAlley]

Originally Posted by andy

It's best to keep the probe in X10 mode unless you're looking at very low level signals. A x10 probe provides a higher input impedance 10M, instead of 1M), so it won't load down the signal as much. It also provides some over voltage protection to the scope since there is a 9 meg resistor in series with the signal. If you forget it's in X1 mode and accidentally touch something with a high voltage on it, you could easily damage the scope. In 10X mode, the worst that's likely to happen is damaging the probe.

Anything 40V and over I use the 10x.

I just about drove myself crazy wondering why I could see the ripple of AC on the DC lines, but couldn't see the DC. I thought I had all the settings correct, but still couldn't see a waveform. After realizing I wasn't going to figure it out on my own, I search the net. I figured out how to measure the voltage of DC, but still can't get a waveform. So does the DC on the B+ have a waveform? If so, how do I see it? What would be the settings other than DC coupling?

Thanks