Author Topic: Idiot-proof Beginner Oscilloscope for Audio and TV repair and fun  (Read 2325 times)

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Online NE666

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Re: Idiot-proof Beginner Oscilloscope for Audio and TV repair and fun
« Reply #25 on: December 17, 2024, 07:23:20 pm »
The best scope to probe things like this is an old Philips/Fluke scopemeter

I'll offer a +1 for that suggestion. Whenever I've needed to diagnose the operation of a suspect SMPS, my old Fluke 867B "Graphical Multimeter' has been sufficient. It samples at just 5M points/sec, and manages just 4 screen updates per second. Still tells me everything I need to know but it does so whilst also being CATIII rated at 1000v and not electrically grounded. And that's Fluke CATIII, not ali express CATIII.
 

Offline timeandfrequency

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Re: Idiot-proof Beginner Oscilloscope for Audio and TV repair and fun
« Reply #26 on: December 17, 2024, 11:47:44 pm »
Hello achugh,

All of the explanations and hints given by @tggzzz, @KungFuJosh, @Conrad Hoffman, @Fungus, @AVGresponding and @NE666 are wise and of great value.

If you need to probe on live circuits and really want to use an oscilloscope, today's safest method is using :
1) a truly isolated scope
or
2) differential probes + non isolated scope.

Or use a good CAT III multimeter.

Everything else is much less safe, or worse, it gives you a false sense of safety.

You may read this thread : When (where) is it safe to measure with oscilloscope and follow the links in the different posts.
« Last Edit: December 18, 2024, 12:00:07 am by timeandfrequency »
 
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Offline J-R

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Re: Idiot-proof Beginner Oscilloscope for Audio and TV repair and fun
« Reply #27 on: December 19, 2024, 06:41:45 am »
I'm all for buying new gear, but perhaps knowledge is the more powerful asset...
 
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Offline wasedadoc

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Re: Idiot-proof Beginner Oscilloscope for Audio and TV repair and fun
« Reply #28 on: December 19, 2024, 10:15:31 am »
I'm all for buying new gear, but perhaps knowledge is the more powerful asset...
Just as writing it on a whizzo word processor does not guarantee your novel will be a best seller.
« Last Edit: December 19, 2024, 10:31:50 am by wasedadoc »
 

Online Aldo22

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Re: Idiot-proof Beginner Oscilloscope for Audio and TV repair and fun
« Reply #29 on: December 19, 2024, 02:32:41 pm »
Thanks to everyone who has answered my question here:-+

My question was a bit vague. I was in the context of “two channels with invert-and-add” and I should have been more specific. My point was not to float the scope.

Now I've played with that a bit.

First of all, on a DSO, Math: subtraction is probably easier than invert+add. That amounts to the same thing, doesn't it?

Then I played with my FY3200. It doesn't come with a 3-wire cable. I made one myself, whereby I can switch the PE on/off.

If it is grounded, then the 2nd channel is of course without signal. So this method is useless.



If it is not grounded, then there is so much voltage on it (90Vrms) that you can hardly see the signal.



However, it works really well with a battery-powered signal generator.
« Last Edit: December 19, 2024, 02:36:49 pm by Aldo22 »
 

Offline achughTopic starter

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Re: Idiot-proof Beginner Oscilloscope for Audio and TV repair and fun
« Reply #30 on: December 27, 2024, 12:02:00 am »
Thank you AVGresponding for sharing Tek THS7xx series.

Thank you tggzzz for responding to me specific questions. If you have some time, can you please look into my subwoofer amp humming issue at https://www.eevblog.com/forum/repair/repair-help-dayton-audio-sa1000-subwoofer-amp-emitting-ac-hum/ and share some pointers for me?

Thank you to all who have contributed so far. I am reading all the valuable and important information shared. It will take me few days to go through the plethora of information already shared.
 

Offline Alex Eisenhut

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Re: Idiot-proof Beginner Oscilloscope for Audio and TV repair and fun
« Reply #31 on: December 27, 2024, 01:42:25 am »
Also read the specs of your probes, there is a voltage derating curve with frequency that's quite surprising.

I once thought I'd tool around inside trashed TVs for fun, I have a 100X 120MHz probe rated for 1.5KV (P6009), so no problem right?

I decided to probe some HV point in the TV and I heard a squeal and a pop and saw smoke come out the compensation box of the probe.

Hm, that high voltage rating goes down real fast after 1 MHz or so.

I fixed the probe but my pride is still hurt.

I leave TVs in the trash now. (Unless it's an awesome CRT set)
Hoarder of 8-bit Commodore relics and 1960s Tektronix 500-series stuff. Unconventional interior decorator.
 
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