Oscilloscope

**tom66** · 12-28-2011, 07:04 PM

Re: Oscilloscope

I have two oscilloscopes.

One 100 MHz digital storage scope used for most of my non repair work as it's only 250V maximum input rated and poor single shot capability. (HP 54501A, cost me £150.)

And one 20 MHz analog scope (cost £60), which I have used successfully to repair two plasma TVs; I chose it for 400V inputs and despite what people have said, with care a 20 MHz scope is sufficient for debugging a 720p plasma (and resolved an okay waveform on a 1080p Panasonic) although you are limited in the higher frequency ranges and you have to turn the intensity right up (and lose a bit of focus control). The most common adjustment is the Vsetup and Vsetdn (or Yfr/Yrr) which can be done if you can read 1/5th division.

**PCBONEZ** · 12-28-2011, 09:57 PM

Re: Oscilloscope

Originally posted by TheLaw

I just snagged a 100Mhz Tek 465M for $70 shipped off eBay.

It's sweet.

I used LOTS of those.
Military version of the 465B.
Very good scope but it's analog.
.
Did you get the hard-shell front cover with it?
.

**Peter9DO** · 12-28-2011, 10:47 PM

Re: Oscilloscope

I got the hard shell cover for the front. The original manuals, the manual holder and it's in VERY good condition! I will post a picture of it here in a little while.

**retiredcaps** · 12-28-2011, 11:01 PM

Re: Oscilloscope

Originally posted by Peter9DO

it's in VERY good condition!

From your description in post #36, I'm sure the guy selling takes care of his stuff and probably a little sad to see it go.

**Peter9DO** · 12-28-2011, 11:18 PM

Re: Oscilloscope

Originally posted by PCBONEZ

Yes.
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Here are the specs for the 'stock' probes for that.

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Need to get probes with a compensating range that covers the input capacitance.
.
Need to get probes with the correct input resistance.
.
Both the above are different between 1x and 10x probes.
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You probably want at least one of each of 1x and 10x or one with a 1x-10x switch.
[If you connect to 50v with a 10x probe the scope only sees 5v.]
.
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When you get the probes connect to the test signal and adjust the compensation for a nice square square-wave on the screen.
[That takes out error due to the cable size and length and the probe.]
The adjuster is usually a very small screw. Location varies.
Could be near the connection to the scope or on the probe itself.
.

By the way, thank you for finding this PDF for me! Here are the images of my purchase.

Attached Files

**PCBONEZ** · 12-29-2011, 09:02 AM

Re: Oscilloscope

Looks like a runner.
.
See where it says "Probe Adjust, 500 mV P-P, 1kHz".
That's the port to adjust compensation on the probes I mentioned earlier.
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**Peter9DO** · 12-30-2011, 10:41 PM

Re: Oscilloscope

Yea, I was probing that hole... lol! You know I looked all over the internet today for about an hour and I was not able to come across a digital format of the service manual, however I did find a hard copy someone was trying to sell for $100 (that's a little crazy). Oh well it, is what it is, maybe one day I will be able to come across one. Anyways! To everyone that posted on this thread (especially PCBONEZ & RetiredCAPS) Thank you very very very very very very very very MUCH! For all the help on giving me some information on what to look for when purchasing an oscilloscope! You guys are awesome! I have borrowed some probes from my cousin (until the ones I ordered from eBay come in) and have been playing with this thing for a couple of hours now. Again, thank you for all the help!

Okay, I have one more question, this is on the use of the oscilloscope. When you are testing the circuit of a power supply for a computer should you have the power supply plugged in to the DC outlet or do you keep all flowing current off during testing? Just a little confused? I'm getting a reading when there is no power being put threw it and I'm scared I'm going to mess the oscilloscope up if the power supply is plugged in, so I have not tested it while it has been plugged in.

-Pete

**retiredcaps** · 12-31-2011, 01:15 AM

Re: Oscilloscope

Originally posted by Peter9DO

Y I was not able to come across a digital format of the service manual,

Ask on eevblog.com. Tekfan might have one. He restores old Tek scopes.

**Agent24** · 12-31-2011, 02:49 AM

Re: Oscilloscope

Originally posted by Peter9DO

Okay, I have one more question, this is on the use of the oscilloscope. When you are testing the circuit of a power supply for a computer should you have the power supply plugged in to the DC outlet or do you keep all flowing current off during testing? Just a little confused? I'm getting a reading when there is no power being put threw it and I'm scared I'm going to mess the oscilloscope up if the power supply is plugged in, so I have not tested it while it has been plugged in.

-Pete

Measuring the PSU while unloaded won't tell you much, you need to load the PSU if you want to know what kind of ripple\noise is going to be coming out when it's under normal conditions.

You won't damage anything by having it powering something or not, but I think if it's connected to a motherboard you might get extra noise coming FROM the motherboard etc and that can affect your reading.

**Th3_uN1Qu3** · 12-31-2011, 06:28 AM

Re: Oscilloscope

Um, of course you plug it in. If there's no power to the thing there will be no electrical signals to view obviously. You also use dummy loads to load up the PSU and simulate a real computer, because hooking up a motherboard will affect the readings just like Agent24 said, and you are interested in what's coming from the PSU alone.

The power supply needs to be plugged in AND connected via an isolation transformer to the mains. If you do not have an isolation transformer then DO NOT attempt to probe anything in the PRIMARY section, otherwise you'll blow up the power supply, the scope, or yourself. An alternative to an isolation transformer is to use an inverter or an UPS on battery power to feed the PSU under test. Some people have those lying around.

**Peter9DO** · 12-31-2011, 02:23 PM

Re: Oscilloscope

I felt kind of stupid for asking that, I didn't understand why I was getting a signal off of it when it wasn't plugged in. The only thing I can think of is that the caps have not been fully discharged and I'm getting something off of them. Please keep in mind, I currently have no clue how to use this and I'm just starting my learning process now that I have one to learn on. I know I'm not going to learn it over night, but I just need somewhere to start, I had a broken power supply sitting there so I just took it apart and started messing with it. If you guys have an idea of something that would be more on the beginner level, I have tons of stuff here. computer parts, a bunch of laptops, Plasma TVs, LCD monitors and the list goes on.

**Peter9DO** · 12-31-2011, 02:24 PM

Re: Oscilloscope

Originally posted by retiredcaps

Ask on eevblog.com. Tekfan might have one. He restores old Tek scopes.

Thank you! I posted on the forum! I will check it later to see if I got any response!

Thanks again,
Peter

**PCBONEZ** · 12-31-2011, 02:29 PM

Re: Oscilloscope

For an experience builder use a good PSU and measure the Ripple on each of the outputs.
Don't even need to pull the PSU apart for that.
Will help you get the hang of what the knobs on the scope do.
.

**godin** · 12-31-2011, 02:42 PM

Re: Oscilloscope

"If you do not have an isolation transformer then DO NOT attempt to probe anything in the PRIMARY section, otherwise you'll blow up the power supply, the scope, or yourself"

Is this true???

**PCBONEZ** · 12-31-2011, 02:55 PM

Re: Oscilloscope

#11, #16 and some others.
http://www.allaboutcircuits.com/worksheets/scope1.html

**Peter9DO** · 12-31-2011, 02:57 PM

Re: Oscilloscope

Originally posted by PCBONEZ

For an experience builder use a good PSU and measure the Ripple on each of the outputs.
Don't even need to pull the PSU apart for that.
Will help you get the hang of what the knobs on the scope do.
.

Thanks, I will take a look at it now!

**godin** · 12-31-2011, 03:10 PM

Re: Oscilloscope

Great link, thanks.
I think I am correct in my understanding that the ground clip if it is connected to ground is safe and the best way to measure in the examples given would be with 2 channels both grounded by their clips?

**PCBONEZ** · 12-31-2011, 03:36 PM

Re: Oscilloscope

Originally posted by godin

Great link, thanks.
I think I am correct in my understanding that the ground clip if it is connected to ground is safe ...

No, that's the possible problem.
Depends on what you are calling 'ground' too.
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The clip on the probe is connected to the scope's chassis which is connected to the ground in the scope's power plug.
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If the 'ground' you connect it to isn't at the same potential as the scope's chassis -and- that chassis is connected to line ground then you just made a ground loop current path through site wiring, the chassis under test and the scope.
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I'm a bit beat and I'm not explaining it very well.
Maybe the Boy Wonder from Romania has a good drawing to make it more clear?
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**godin** · 12-31-2011, 03:51 PM

Re: Oscilloscope

Sooo, I think that makes a lot of sense. Therefore the 2 probe 2 channel with no earth clips connected is the correct approach. This would eliminate any chance of potential difference.

**PCBONEZ** · 12-31-2011, 04:04 PM

Re: Oscilloscope

Originally posted by godin

This would eliminate any chance of potential difference.

Maybe not.
- I'm not real clear on what you are doing and I don't want to give you bad advice.
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To get a signal to the scope there has to be a return path [aka reference] for whatever the probe is connected to.
Where is/are your return paths?
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Oscilloscope

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