@Carrington How much spray did you use to cover the inside of the scope?
Nice paint job!
Did you fix your adapter board? Or did you get new boards from Aidatek?
Your final results after the changing of two boards and your works with the spay shielding is marvelous.
Your gnd-noise level of 28mVp-p isn't with a loop cycle of probe cable but with the straight. If you measure it again like as we have said, I am very sure that you'll have under 20mVp-p.
Your test with FFT and the small radio was "all the money"!
The next one for all our forum company is to make a good fw for this oscilloscope and change the label as "AWLtB" (As We Like to Be)"
- Note the peak over 106.5MHz, i.e. internal FM receiver Osc. to get 10.75MHz IF.
Well, now there is not much difference.
The effect of the radio on the FFT is interesting. With the shielding on the cabinet I assume the radiation is coming through the probe cable. Did you try moving the radio further away to see when the effect decreased?
Great work Carrington! I agree with lemon, the demonstration with FFT and radio is really great.
Anyway, I did the backlight mod and it got rid of the peaks in its area. Results are same as lemon's.
I've also changed resistors for the comparator pin of the MC 34063A, but that gave no improvement to the duty cycle issue. It' still changing all the time. I took some time and probed around the PSU and I've noticed that the whole +8.4 V rail is contaminated with noise. I'm not sure from where it could be coming. It doesn't look to me as if the main source could be coming from the MC. I've probed the comparator pin on MC and results are attached. I also removed the capacitors that were going from the resistors to ground at the sense pin. This made the noise a bit clearer to see.
Basically the noise is cyclic and here's how cycle looks like: First, there's the quiet period seen on the left side of the picture. Here we have the usual switching noise from the MC. Then near the trigger point, comes the first wave of the noise. Then there's a short quiet period (10 microseconds here). After it comes the second noise noise wave. After comes the long quiet period. I'm also not sure how to actually trigger on this event. I captured it by repeatedly pressing the single button.
The probing was done with the oscilloscope running on battery.
If I understand how this PSU works, when on battery, everything south of D8 should be off. This means that the only two ICs running are the MC34063A and the LM324. The LM shouldn't do anything smart when the PSU is running on the battery. My idea is to try replacing it and see if anything happens. I'll also see if I can re-trace the board and make a schematic of the area near the LM. In my version of the PSU, all four op-amps are in use.
If this doesn't help, I'll see if I can run the PSU without both the MC and the LM.
The effect of the radio on the FFT is interesting. With the shielding on the cabinet I assume the radiation is coming through the probe cable. Did you try moving the radio further away to see when the effect decreased?
Obviously that's what happens.
- "Radio Osc" -> 106.5MHz + 10.75MHz. Away from gnd loop ~1cm.
- "Cadena Ser" -> 106.5MHz FM. Away from gnd loop ~1Km.
As far as I know, you are right in all the assumptions about how the circuit works. I assume you are doing all testing in the no-electronics room, so we can assume there is no external interference. I doubt that the LM can cause any trouble here, but you can probe the output pins to see if there are any oscillations. The noise in the 8.4V rail may be causing the MC to misbehave, there are not very many other suspects, since I think you have replaced just about every component in that area. There may be something wrong with the battery itself, or its protection circuits. Have you tried a ferrite on the battery cable to see if this reduces the noise on the 8.4V rail?
I added a ferrite to the battery lead, but it did not help. I also removed the PSU from the scope and did some measurements with it connected only by cables. The Z-plate is still full of noise spikes and I think that the noise could be coming from the Z-plate to the PSU. The type of noise I previously described to me seems a bit stronger on the Z-plate than on the PSU ground. That should be expected, since I have ferrite on PSU to adapter board cable.
A few things to try out:
I have a linear PSU which should be capable of outputting up to 2 A. If that's enough I could try running the scope from that and another battery (for negative voltage) and see the amount of noise inside the scope. This should allow me to see how much noise is generated by the adapter board and the main board by themselves.
Next, I could run the PSU with a dummy load and see how it behaves. If the previous step works out fine, I could easily test that out, otherwise I'd have to wait for access to another scope.
Yes, I get the new boards from Aidetek, but this was not easy. Owon don't want selling directly to me the adapter board. Why? I don't know.
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Without the shield and using the short gnd probe cable the noise was around 50 mV.
Well, now there is not much difference.Looks like 5mVpp better!
When the GND noise is that low a few millivolts less are hard to achieve. With the ferrites on my probes my noise is still a little higher than that. However, the position of the probe cables in respect to the scope don't have much of an effect.
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Anyway, I did the backlight mod and it got rid of the peaks in its area. Results are same as lemon's.
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How can I save to external usb stick or to pc via Oscilloscope software a record waveform?
For example go Save->Type-Record->Mode-Record and click to Operate-Play, when you want to stop press simple the Click.
If you want to see what you have record follow the Mode-Playback->Operate-Play. With the Playmode-Loop the capture waveform plays without stop.
Just fine until now, but I can't find how this captured waveform can to export.
How can I save to external usb stick or to pc via Oscilloscope software a record waveform?
For example go Save->Type-Record->Mode-Record and click to Operate-Play, when you want to stop press simple the Click.
If you want to see what you have record follow the Mode-Playback->Operate-Play. With the Playmode-Loop the capture waveform plays without stop.
Just fine until now, but I can't find how this captured waveform can to export.As far as I can see, you can only save to internal memory. I don't see any way of exporting to USB stick or PC.
I also noticed that when I use this function it interferes with the AC trigger. Once I use it, AC trigger don't seem to work until I change to DC trigger. Then, when I change to AC trigger again it works OK.
Also, I noticed that the Record Function is only to view the waveform to loop or at once, not to stop this and zoom with Time button. If you try this you'll laugh a lot of...