Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old May 3rd 21, 11:55 PM posted to sci.electronics.repair
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Default tests to do on used oscilloscope?

Jason Bowers wrote:

==================

A small 1x 10x probe arrives today at last so I can at least check the
scope's square wave output signal peg. See what happens then.

The frequency still seems to be showing higher than it actually is
though. Even with a 30 Mhz scope like this, should I be able to "zoom"
in to see just one or two waveforms? So far, I can't seem to get closer
than 4-5 waveforms at 28 Mhz even with the 10x magnifier on.


** Completely normal.

28MHz is at the limit of the scope's range so no detail is visible on a sine wave.
Also, the amplitude will by down by 30% or so from that at say 5MHz.

30 MHz scopes are are not "flat" to 30MHz but will be at least 3dB down.


....... Phil

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Old May 4th 21, 10:59 AM posted to sci.electronics.repair
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Default tests to do on used oscilloscope?

On 5/3/21 6:55 PM, Phil Allison wrote:
Jason Bowers wrote:

==================

A small 1x 10x probe arrives today at last so I can at least check the
scope's square wave output signal peg. See what happens then.

The frequency still seems to be showing higher than it actually is
though. Even with a 30 Mhz scope like this, should I be able to "zoom"
in to see just one or two waveforms? So far, I can't seem to get closer
than 4-5 waveforms at 28 Mhz even with the 10x magnifier on.


** Completely normal.

28MHz is at the limit of the scope's range so no detail is visible on a sine wave.
Also, the amplitude will by down by 30% or so from that at say 5MHz.

30 MHz scopes are are not "flat" to 30MHz but will be at least 3dB down.


...... Phil


Thank you and the others here! The scope seems fine. I was finally
able to find out what happened to the square wave test peg. It
dislodged during shipping. Reattached and a nice 2V PP 1 Khz square wave.

Phil, what you said was confirmed. If I input the signal generator and
set for say 10 Mhz, the frequency and amplitude are spot on.
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Old May 4th 21, 12:43 PM posted to sci.electronics.repair
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Default tests to do on used oscilloscope?

Jason Bowers wrote:
===================

** Completely normal.

28MHz is at the limit of the scope's range so no detail is visible on a sine wave.
Also, the amplitude will by down by 30% or so from that at say 5MHz.

30 MHz scopes are are not "flat" to 30MHz but will be at least 3dB down.


...... Phil

Thank you and the others here! The scope seems fine. I was finally
able to find out what happened to the square wave test peg. It
dislodged during shipping. Reattached and a nice 2V PP 1 Khz square wave.

Phil, what you said was confirmed. If I input the signal generator and
set for say 10 Mhz, the frequency and amplitude are spot on.


** Thanks for the confirmation.

FYI:
Analog scopes are one of my favorite things.
I currently own 5 of them.

One I built from new parts when I was 17 - way back in 1970.
Uses 5 tubes ( twin triode and triode pentode types ) plus is fully calibrated.

I also own a modern Rigol DSO but don't like it much ....



...... Phil





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Old May 4th 21, 06:51 PM posted to sci.electronics.repair
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Default tests to do on used oscilloscope?

On 5/4/21 10:07 AM, Ralph Mowery wrote:
In article , says...

Thank you and the others here! The scope seems fine. I was finally
able to find out what happened to the square wave test peg. It
dislodged during shipping. Reattached and a nice 2V PP 1 Khz square wave.

Phil, what you said was confirmed. If I input the signal generator and
set for say 10 Mhz, the frequency and amplitude are spot on.



Glad the scope checked out for you.

As far as the scope showing 2 or 3 waves at 30 MHz instead of one, that
is probably normal. I checked out my Tecktronics 465B scope which is a
100 MHz scope and with the 10x button pushed in it shows several waves
instead of just one at 100 MHz.

I think Phil mentioned it tht a scope is usually spected at a 3 db or
some other figure down at the rating. Just like the 30 MHz scope has
mostly full specs at 10 and not 30 MHz but is usuable to 30 and maybe
some what more to look at waveforms. Then there is that square wave
vers sine wave where you need a lot higher rated scope to show a true
square wave than a sine wave.



Well, I know the thread has been kindly answered and discussed now,
thanks mostly to Phil and you, I did want to tag on another question
while I was at it: is there any way to determine when this scope might
have been made? As mentioned, it is the Elenco S-1325. To my surprise,
it apparently is still being made but who knows for how long. Just a
curiosity more than anything else. Certainly seems clean enough.

Thanks once again guys.
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Old May 5th 21, 12:26 AM posted to sci.electronics.repair
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Default tests to do on used oscilloscope?

Ralph Mowery wrote:
===================


I also own a modern Rigol DSO but don't like it much ....


Phil does your Rigol DSO work well in the X/Y mode ?


** Nope.

Does Lissajous patterns bout as well as a dog waking on its hind legs.


I am like you, for many things I perfer the Techtronic 465B scope I have
over the DSO, but for some things the DSO is better for me.


** Yep, I drag it out only for special jobs like one shot events.

I did build a 2 inch scope in high school. I think it only had 3 tubes
that handled the signals. One for the horizontal, one for the vertical,
and one for the sweep generator. Couple of more were rectifiers. It
probably topped out not much above the audio range.


** Still better than having no scope.
My 3 inch tube scope does 2MHz.

...... Phil
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Old May 5th 21, 07:35 AM posted to sci.electronics.repair
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Default tests to do on used oscilloscope?

On Mon, 3 May 2021 10:04:50 -0400, Ralph Mowery
wrote:

In article ,
says...

my signal generator outputs some wonky voltages unless you have a load
resistor across the outputs. It's 600ohms in a box with 1" spacing banana
plugs and receptacles. I could never figure out why that's not handled by
a pushbotton.

Also, make sure you don't have any knobs pulled out putting you in zoom
mode. My signal generator has one of silly scope knobs too for some
reason.



Signal generators are designed to put out a certain voltage into a
certain load. Think of them as having a signal generating source of
zero impedance in series with a resistor. Any load will devide between
the internal impedance and the load impedance.

For RF generators there were two standards. One was an open circuit Or
very high impedance) voltage and the other was for a 50 ohm load. My
service monitor has a software setting to do either one. It is from the
old analog cell phone days and 30 years ago the cost was about $ 50,000.
When the cell phones went digital the service monitor was put out for
surplus and are selling for under $ 1000 now on the used market.

When using a scope you have to allow for the peak or peak to peak ratio
to the RMS value of a sine wave. As mentioned before I don't recall the
ratio as I seldom need it and the scope I have now will calculate it and
put on the display. If your RMS meter shows abot 120 volts AC out of
the wall socket a scope will show around 170 volts peak.


My signal generator is an all valve (four) unit and it works
from 5 Hz to 600 KHz.


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