Need Some Oscope Pointers

[Phoenixcolt]

Sup everyone, got a pocket oscope a while back and am starting my installation, ran all the wires, just need a bit more time to get everything situated.

Today I was measuring for headunit clipping as step 1, and even though I shut off all of the signal processing and evened out all of the attenuation, I couldn't get my 50 Hz signal wave to look like a normal wave. It seemed to be jumping around and not giving me any kind of steady wave.-Why would this happen?

Next I tried measuring for 8V voltage at the line driver output, and I couldn't get any kind of ac voltage read with the dmm or oscope.-Should I attach a signal cable and see if I can get a read off of that versus the line driver signal output? Or am I just doing something wrong?

Hope someone can give me a hand, I am sure I will have more questions as I try to get deeper into this.

Thanks.-Mike

[Eric D]

Off hand it sounds like you might have a ground problem.

What kind of cables are you using for the o-scope?

[zztunnell]

Off hand it sounds like you might have a ground problem.

What kind of cables are you using for the o-scope?

What kind should we be using? The old school scope I picked up a few ago didnt have any. The guy at radioshack said to use regular test probe leads. I was thinking I needed sheilded ones or something idk. Im an oscope newbie and have no idea what all the knobs and hook ups are for.

Sorry to kinda hijack this thread but figured it was better than starting a new one.
added pic

[ttocs]

You need a probe, and a ground. A lot of probes will have a spot on it for ground to make it easy but if not, that is why you have the ground input on the bottom as well.

[ttocs]

also some probes will provide an amplifying/resistive effect so that they show 10x what the reading is, or shows 1/10 what the reading is just in case you are reading a high/low voltage. They will normally say on the probe somewhere if they do this.

[Phoenixcolt]

Sweet! Thanks for the replies guys, I am away from home tonight but I will take a couple pics tomorrow and post, glad you guys can help : ), i need it.

[ttocs]

looking at the scope it looks like you have the hor sweep set up to high if you are trying to measure 50 hz as well as with the sync set to ext I think its looking for some type of external triggering device to set up its sweep/sync rate. It also looks like you have it set up to read DC voltage rather then ac if that pic of the scope was after you tried to use it.

[zztunnell]

That pic was the 1 copied from craigslist before i bought it.I havent plugged it in since i bought it. I been trying to figure out how to use it online when I have extra time.

Still working on building my work bench.

[zztunnell]

You need a probe, and a ground. A lot of probes will have a spot on it for ground to make it easy but if not, that is why you have the ground input on the bottom as well.

Anyone know a good place to source the correct cables?

[ttocs]

Not for that one. Most of them use a BNC connector I think not sure about with banana clips.

[Phoenixcolt]

Off hand it sounds like you might have a ground problem.

What kind of cables are you using for the o-scope?

Here is what I have, DSO201 Nano. I was clipping the banana clip to the outside of my signal cable, and I used the probe to touch the male part of the signal cable. Not sure how else to go about it. Should I have grounded to a completely separate ground?

[Phoenixcolt]

Another question, do I need to convert the realm of excursion test tones from mp3 or should those be ok as they are?

[Eric D]

That probe and the way you were connecting it should be fine.

If you start with a 60Hz tone out of the head unit, at about half volume, you should play with the settings on the o-scope until you get a clean signal displayed.

You may have the trigger set out of the range of the signal, so the scope cannot track it. I would keep playing around until you see something good and then make note of what you did. The nano should be simple enough with its settings to get something displayed without too much effort.

If the input jack of the nano is a mini jack for example, I suggest you get a mini to RCA adapter, as it would make life easier to just plug the nano into your RCA outputs and not have to hold the probe on the connection.

[Phoenixcolt]

Seriously can't get much better a read than the below and that won't get me a consistent frequency read, I don't get it. Could it have anything to do with the full range speakers remaining hooked up? Initially I disconnected the positive on each speaker lead from the headunit and got a similar result so I am not sure it has anything to do with the speaker leads.

[Eric D]

Are you measuring the speaker outputs of the head unit, or the RCA jacks? If you have speakers connected to the head unit, you should disconnect them, as sine waves can kill them. And, with the RCA cables disconnected, you should not have any other speakers playing as well.

[Phoenixcolt]

Are you measuring the speaker outputs of the head unit, or the RCA jacks? If you have speakers connected to the head unit, you should disconnect them, as sine waves can kill them. And, with the RCA cables disconnected, you should not have any other speakers playing as well.

I was measuring the headunit sub preout (sub rca).

If I cut an old rca, and then strip it, maybe I can get a better read if I connect the pos and neg oscope leads to the stripped rca leads, and if that doesn't get me a better read, I dunno what's going on.

Hopefully it will work at the amp speaker outputs if nothing else.

[ttocs]

what are the cross over settings that you have for the subwoofer output? IE you don't have it crossed over at 50 hz or below do you?

[Phoenixcolt]

what are the cross over settings that you have for the subwoofer output? IE you don't have it crossed over at 50 hz or below do you?

Funny, with that question I just realized I don't have a low pass filter on this deck, it's the Alpine INA-W910.

There is however a bass center frequency and width adjustment. I wonder if the center frequency set at 63Hz, even though it isn't boosted, is causing my problems.

So I will try again this afternoon, this time I will bump the bass center frequency up to like 200 or so and see if I can get a steady wave.

[ttocs]

you should have all the setting for bass/treble set to 0 before tuning.

[Eric D]

The signal shown on the display looks a lot more like music than it does a sine wave. Are you sure you are playing a tone of a single frequency, and not some into music track or something?

[Phoenixcolt]

you should have all the setting for bass/treble set to 0 before tuning.

I do all of that but I am wondering if even though I have the bass center frequency at 63, with 0 db of boost, if it is still throwing off the signal. There is a bass width adjustment as well, so perhaps I need to confirm that is at it's widest setting as well.

[Phoenixcolt]

The signal shown on the display looks a lot more like music than it does a sine wave. Are you sure you are playing a tone of a single frequency, and not some into music track or something?

Pretty sure since when I play it with the speakers still connected (I know I shouldn't), I can hear the 50 Hz signal. Could it have anything to do with it being an mp3 file? I got it from realm of excursion but it's in mp3 at 0dB so I thought it would be ok.

[ttocs]

I don't understand it either it says it is a 54 hz signal which is close but doesn't look like one.

[Phoenixcolt]

I can't get a clean wave on the oscope no matter what I do, maybe I changed a range at some point and can't get back to ground zero, I am so frustrated.


Then to top it off, I tried at least adjust the gain with a DMM and I couldn't get a read off the amp speaker terminals, the amp kept popping into a safety mode, giving me a blinking blue light. I have never had that happen to me before. Any ideas why I could be seeing this happen?

[trickyricky]

The scope might be faulty, only way to check it would be with another scope (to verify that its either your scope or your head unit not been able to pick up/play sine waves).