Probing random things with my scope

[Stonent]

I was probing around a wireless router last night and found a point that generated about a 1 inch solid strip on my scope. I kept adjusting the time until I could just barely see the wave form. Then I pulled my X5 magnification button and got two overlaying sine waves that were sort of flickering. I found about a range of 2mm or so on my trigger knob that could almost get me a clear waveform (here). Since I was having such a hard time isolating that trace, I was thinking that I might be at the limit or possibly exceeding the range of my scope (20MHz)



So my brain isn't doing a very good job right now and I'm trying to figure out the frequency.

I'm on .2 uS/Div and x5 magnification so that's .04uS/Div, right? From what I can tell, I'm just about getting 1 complete wave per division at this scale so what frequency does that look like to you?

Also found this on the output of what I thought was a voltage regulator.



What I was interested in is that it looks like a square wave but the top is 1.5 divisions and the bottom is 2 divisions.  Is it more likely that the wave is being generated that way or that there's something going on with my scope? I'm at 2uS per division on this wave with no magnification.  The 10K test signal on the scope is pretty much spot on. Also interesting is that this device has 12VDC going in and what I thought were pins with 5V and 8V. Turns out the 8V is really 9VAC but the cheap volt meter I was using didn't seem to care all that much.

[c4757p]

First one looks like a failure to trigger. 25 MHz (1/40ns) on a 20 MHz scope - a bit surprising, but not entirely uncommon depending on the scope, that it couldn't trigger.

Edit: just under 50 MHz actually, I see almost two complete cycles per division. Less surprising now. My old 20 MHz wouldn't trigger on a 50 MHz wave either.

Second probably is the output of a voltage "regulator" - a DC/DC converter, before it goes off to the rest of the circuit.

[Stonent]

First one looks like a failure to trigger. 25 MHz (1/40ns) on a 20 MHz scope - a bit surprising, but not entirely uncommon depending on the scope, that it couldn't trigger.

Edit: just under 50 MHz actually, I see almost two complete cycles per division. Less surprising now. My old 20 MHz wouldn't trigger on a 50 MHz wave either.

Second probably is the output of a voltage "regulator" - a DC/DC converter, before it goes off to the rest of the circuit.

You are absolutely correct. I just now happened to find a picture of the circuit board and it was this:

http://www.diodes.com/datasheets/AP1506.pdf

A 1506 150KHz, 3A PWM BUCK DC/DC CONVERTER.  The PWM would explain the inconsistency in the wave size.

And here it is in circuit.



Just like the example, a coil, schottky, some resistors and some capacitors.

There is a 16MHz crystal elsewhere so maybe something is tripling the clock which would make it around 48MHz in that case?