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 January 25th 19, 05:19 PM posted to sci.electronics.repair
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Default Bad probe-what's wrong?

On Thu, 24 Jan 2019 14:55:53 -0800 (PST), wrote:

On Thursday, January 24, 2019 at 5:28:49 PM UTC-5, wrote:
On Thu, 24 Jan 2019 13:38:54 -0800, Paul Drahn
wrote:

On 1/24/2019 1:27 PM,
wrote:
On Thursday, January 24, 2019 at 2:23:49 PM UTC-5, wrote:
I got my new to me BK precision 4001A function generator and I
thought I would see what it does. Tried looking at square waves but
they weren't square. The probe is a Probe Master 100 MHz. So, trying 3
other probes the display shows nice square waves. Using the output on
the TEK 465B 'scope itself also shows nice square waves.
The display should show horizontal lines 1 division long and
separated by 1.5 divisions, according to the dial settings on the
'scope. But instead the lines sweep up and down from the center and
the closest points of the lines are only about 1/5 of a division
apart.
I tried adjusting the probe by turning the adjusting screw with an
insulated screwdriver, and although it does flatten the shape some it
does not fix it.
So the probe must be trash but what could cause this behavior?
Thanks,
Eric

Do you mean you're seeing more of a triangle wave with 1/5 div peak to peak?

Perhaps the prob has been repaired and the wrong coax used. Probably
should be 95-100 ohm.

Paul

I bought the probe new many years ago and have never seen any reason
to repair it. There is no obvious damage. Could dropping it have
caused the problem?
Eric


Oh, it worked in the past? Or maybe you've never had a good square wave
to check it with?

GH

Yeah, it worked in the past using the square wave output on the
'scope.
Eric

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Old January 25th 19, 06:52 PM posted to sci.electronics.repair
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Default Bad probe-what's wrong?


1. The adjustment only works in anything but x1 mode.

2. The adjustment corrects the squareness of a square wave. It makes the divider resistive.

3. Probes are designed for a certain input Z e.g. 1 M 22 || pf and freq response
Make sure the scope isn't 50 ohms.

4. For the adj, the scope should be DC coupled.

5. Scope could be in UNCAL mode. Freq or voltage.

6. Check voltage with a DC source. Freq: Try the AC line for frequency.

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Old January 26th 19, 12:06 AM posted to sci.electronics.repair
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Default Bad probe-what's wrong?

On Fri, 25 Jan 2019 10:52:54 -0800 (PST), "Ron D."
wrote:


1. The adjustment only works in anything but x1 mode.

2. The adjustment corrects the squareness of a square wave. It makes the divider resistive.

3. Probes are designed for a certain input Z e.g. 1 M 22 || pf and freq response
Make sure the scope isn't 50 ohms.

4. For the adj, the scope should be DC coupled.

5. Scope could be in UNCAL mode. Freq or voltage.

6. Check voltage with a DC source. Freq: Try the AC line for frequency.

That DC couplng migt be the problem. It was mentioned in another post
too. Tomorrow I will check things again with the 'scope properly set
up and report back.
Thanks,
Eric
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Old January 26th 19, 12:08 AM posted to sci.electronics.repair
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Default Bad probe-what's wrong?

On Thu, 24 Jan 2019 14:53:30 -0800 (PST), Terry Schwartz
wrote:

On Thursday, January 24, 2019 at 1:23:49 PM UTC-6, wrote:
I got my new to me BK precision 4001A function generator and I
thought I would see what it does. Tried looking at square waves but
they weren't square. The probe is a Probe Master 100 MHz. So, trying 3
other probes the display shows nice square waves. Using the output on
the TEK 465B 'scope itself also shows nice square waves.
The display should show horizontal lines 1 division long and
separated by 1.5 divisions, according to the dial settings on the
'scope. But instead the lines sweep up and down from the center and
the closest points of the lines are only about 1/5 of a division
apart.
I tried adjusting the probe by turning the adjusting screw with an
insulated screwdriver, and although it does flatten the shape some it
does not fix it.
So the probe must be trash but what could cause this behavior?
Thanks,
Eric


Sounds like it's AC coupled.

It is. DC didn't seem to change things but I don't know. Tomorrow I
will have time to set everything properly and will report back.
Thanks,
Eric


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