Does anyone have schematics or suggestions for repairing a Tek P6563A scope probe? The problem is the signal line has only a 390 ohm resistance to the shield as measured with a DMM.

On 7/22/2014 11:15 AM, wrote:
Does anyone have schematics or suggestions for repairing a Tek P6563A scope probe? The problem is the signal line has only a 390 ohm resistance to the shield as measured with a DMM.

What exactly are you measuring?
If you are measuring in the X1 mode from the tip to the center conductor
of the BNC 390 ohms might be right. My elcheapo probe measures 250 ohms.

Are you really measuring from tip to shield?

What is the symptom?
Mikek

On Tuesday, July 22, 2014 1:04:33 PM UTC-4, amdx wrote:
On 7/22/2014 11:15 AM, wrote:
Does anyone have schematics or suggestions for repairing a Tek P6563A scope probe? The problem is the signal line has only a 390 ohm resistance to the shield as measured with a DMM.

What exactly are you measuring?

If you are measuring in the X1 mode from the tip to the center conductor

of the BNC 390 ohms might be right. My elcheapo probe measures 250 ohms.

Are you really measuring from tip to shield?

What is the symptom?

Mikek

Hmm...you are right, I was measuring center conductor to shield. Measuring tip to shield gives about 9M (pretty darn close to the 9.5M it says on the probe).

The problem is if I remove the shield (the part that's springy and spins around) and just connect the center conductor pin to the scope, it works: I see a square wave riding on a 60Hz sinusoid (since there's no shield connection). The probe tip is on the square wave cal output of my scope (5V @ 1kHz).

As soon as I put the springy/spinny part back on (I guess Tek calls this the "BNC Shell") my scope reads 0V. This is what lead me to believe there was some kind of internal short between the center conductor and the shield.

On 7/22/2014 12:17 PM, wrote:
On Tuesday, July 22, 2014 1:04:33 PM UTC-4, amdx wrote:
On 7/22/2014 11:15 AM, wrote:
Does anyone have schematics or suggestions for repairing a Tek P6563A scope probe? The problem is the signal line has only a 390 ohm resistance to the shield as measured with a DMM.

What exactly are you measuring?

If you are measuring in the X1 mode from the tip to the center conductor

of the BNC 390 ohms might be right. My elcheapo probe measures 250 ohms.

Are you really measuring from tip to shield?

What is the symptom?

Mikek

Hmm...you are right, I was measuring center conductor to shield. Measuring tip to shield gives about 9M (pretty darn close to the 9.5M it says on the probe).

If you are measuring tip to shield, that means you have short between
the center wire and the cable shield. See terms defined below.
However, I don't think you are measuring tip to shield.


The problem is if I remove the shield (the part that's springy and spins around) and just connect the center conductor pin to the scope, it works: I see a square wave riding on a 60Hz sinusoid (since there's no shield connection).

The probe tip is on the square wave cal output of my scope (5V @ 1kHz).

As soon as I put the springy/spinny part back on (I guess Tek calls this the "BNC Shell") my scope reads 0V. This is what lead me to believe there was some kind of internal short between the center conductor and the shield.


I think we need to define terms. Shield on a scope probe usually
means the outer conductor of the cable which is a coaxial braid around
the center wire.

The BNC connector is the part that makes a 1/2 turn to connect to the scope.

On the other end (the tip that you place on a test point) there is an
accessory called the Retractable hook tip it slips on the end of the
probe.

Sense you are using the scope internal calibrator, I would connect it
and start wiggling the bnc end and see if the display corrects.
If not wiggle the end connected to the calibrator point.

It seems like you have two problems, an open shield at one end or the
other, and your Retractable hook tip is not making the connection to the
tiny point sticking out of the end of your probe.
It may be as simple as pushing it on just a little further.

Keep going, we will get on the same line of thinking and solve the
problem.
Mikek

OK, sorry for top-posting but a picture is worth a thousand words. BTW, thanks for helping with this.

Here is what's going on: https://www.flickr.com/photos/andrew...7645862229985/

1. Just a shot of the inside of the probe

2. No BNC connector, not probing anything: we're just getting noise

3. No BNC connector, the tip touched to the shield

4. No BNC connector, the ground clip (next to the tip) touched to the shield

5. No BNC connector, the tip touched to the square wave output. Here is what leads me to believe that the tip-to-center-conductor path is OK as it's making it all the way to the scope.

6. But...as soon as I connect the tip AND the ground clip to the square wave output + earth, the signal goes to 0V.

7. Now the BNC connector goes on, the probe is not probing anything, and we have a solid 0V (no noise)

8. The BNC connector is still on, the probe tip is on the square wave output: still 0V

9. The BNC connector is still on, the probe tip and ground clip are on the square wave output+earth: still 0V

10. Just for illustration, a different known-good working probe shows the expected result.

On Tuesday, July 22, 2014 2:29:08 PM UTC-4, amdx wrote:
On 7/22/2014 12:17 PM, wrote:

On Tuesday, July 22, 2014 1:04:33 PM UTC-4, amdx wrote:

On 7/22/2014 11:15 AM, wrote:

Does anyone have schematics or suggestions for repairing a Tek P6563A scope probe? The problem is the signal line has only a 390 ohm resistance to the shield as measured with a DMM.



What exactly are you measuring?



If you are measuring in the X1 mode from the tip to the center conductor



of the BNC 390 ohms might be right. My elcheapo probe measures 250 ohms.



Are you really measuring from tip to shield?



What is the symptom?



Mikek



Hmm...you are right, I was measuring center conductor to shield. Measuring tip to shield gives about 9M (pretty darn close to the 9.5M it says on the probe).



If you are measuring tip to shield, that means you have short between

the center wire and the cable shield. See terms defined below.

However, I don't think you are measuring tip to shield.





The problem is if I remove the shield (the part that's springy and spins around) and just connect the center conductor pin to the scope, it works: I see a square wave riding on a 60Hz sinusoid (since there's no shield connection).



The probe tip is on the square wave cal output of my scope (5V @ 1kHz).



As soon as I put the springy/spinny part back on (I guess Tek calls this the "BNC Shell") my scope reads 0V. This is what lead me to believe there was some kind of internal short between the center conductor and the shield.





I think we need to define terms. Shield on a scope probe usually

means the outer conductor of the cable which is a coaxial braid around

the center wire.



The BNC connector is the part that makes a 1/2 turn to connect to the scope.



On the other end (the tip that you place on a test point) there is an

accessory called the Retractable hook tip it slips on the end of the

probe.



Sense you are using the scope internal calibrator, I would connect it

and start wiggling the bnc end and see if the display corrects.

If not wiggle the end connected to the calibrator point.



It seems like you have two problems, an open shield at one end or the

other, and your Retractable hook tip is not making the connection to the

tiny point sticking out of the end of your probe.

It may be as simple as pushing it on just a little further.



Keep going, we will get on the same line of thinking and solve the

problem.

Mikek



On Tuesday, July 22, 2014 2:29:08 PM UTC-4, amdx wrote:
On 7/22/2014 12:17 PM, wrote:

On Tuesday, July 22, 2014 1:04:33 PM UTC-4, amdx wrote:

On 7/22/2014 11:15 AM, wrote:

Does anyone have schematics or suggestions for repairing a Tek P6563A scope probe? The problem is the signal line has only a 390 ohm resistance to the shield as measured with a DMM.



What exactly are you measuring?



If you are measuring in the X1 mode from the tip to the center conductor



of the BNC 390 ohms might be right. My elcheapo probe measures 250 ohms.



Are you really measuring from tip to shield?



What is the symptom?



Mikek



Hmm...you are right, I was measuring center conductor to shield. Measuring tip to shield gives about 9M (pretty darn close to the 9.5M it says on the probe).



If you are measuring tip to shield, that means you have short between

the center wire and the cable shield. See terms defined below.

However, I don't think you are measuring tip to shield.





The problem is if I remove the shield (the part that's springy and spins around) and just connect the center conductor pin to the scope, it works: I see a square wave riding on a 60Hz sinusoid (since there's no shield connection).



The probe tip is on the square wave cal output of my scope (5V @ 1kHz).



As soon as I put the springy/spinny part back on (I guess Tek calls this the "BNC Shell") my scope reads 0V. This is what lead me to believe there was some kind of internal short between the center conductor and the shield.





I think we need to define terms. Shield on a scope probe usually

means the outer conductor of the cable which is a coaxial braid around

the center wire.



The BNC connector is the part that makes a 1/2 turn to connect to the scope.



On the other end (the tip that you place on a test point) there is an

accessory called the Retractable hook tip it slips on the end of the

probe.



Sense you are using the scope internal calibrator, I would connect it

and start wiggling the bnc end and see if the display corrects.

If not wiggle the end connected to the calibrator point.



It seems like you have two problems, an open shield at one end or the

other, and your Retractable hook tip is not making the connection to the

tiny point sticking out of the end of your probe.

It may be as simple as pushing it on just a little further.



Keep going, we will get on the same line of thinking and solve the

problem.

Mikek

In a case like this I would suspect the cable itself. Over the years they get bent around all over the place, and maybe worse, like being rolled over by a scopemobile or something similr with three hundred pounds of equipment on it.

On 7/22/2014 7:04 PM, wrote:
OK, sorry for top-posting but a picture is worth a thousand words. BTW, thanks for helping with this.

Here is what's going on: https://www.flickr.com/photos/andrew...7645862229985/

1. Just a shot of the inside of the probe

2. No BNC connector, not probing anything: we're just getting noise

3. No BNC connector, the tip touched to the shield

4. No BNC connector, the ground clip (next to the tip) touched to the shield

5. No BNC connector, the tip touched to the square wave output. Here is what leads me to believe that the tip-to-center-conductor path is OK as it's making it all the way to the scope.

6. But...as soon as I connect the tip AND the ground clip to the square wave output + earth, the signal goes to 0V.

7. Now the BNC connector goes on, the probe is not probing anything, and we have a solid 0V (no noise)

8. The BNC connector is still on, the probe tip is on the square wave output: still 0V

9. The BNC connector is still on, the probe tip and ground clip are on the square wave output+earth: still 0V

10. Just for illustration, a different known-good working probe shows the expected result.



Ok, I'm not familiar with that probe, But when you put the BNC
connector back on, do you measure low ohms from the BNC to the other end
of the compensation housing?
Since you have it apart can you measure the cable shield from end to end?
Is it continuous?
Do you think the cable shield makes a good connection to the
compensation housing when you put it together?

You have a funny wire making your ground in the next to the last
picture, what's that about?
Can you post a picture of that end of your probe?
Why not the normal wire with an alligator clip?

I don't think I've helped yet, but gave you some items to check.

Mikek

On Tuesday, July 22, 2014 12:15:42 PM UTC-4, wrote:
Does anyone have schematics or suggestions for repairing a Tek P6563A scope probe? The problem is the signal line has only a 390 ohm resistance to the shield as measured with a DMM.

If you have a x1 probe and it's not connect to the scope (or any other piece of test equipment) then the resistance should be near infinity.

wrote:

On Tuesday, July 22, 2014 12:15:42 PM UTC-4, wrote:
Does anyone have schematics or suggestions for repairing a Tek P6563A scope probe? The problem is the signal line has only a 390 ohm resistance to the shield as measured with a DMM.

If you have a x1 probe and it's not connect to the scope (or any other piece of test equipment) then the resistance should be near infinity.


It is 20X, with the ID pin.


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

On 7/27/2014 5:17 PM, Michael A. Terrell wrote:

wrote:

On Tuesday, July 22, 2014 12:15:42 PM UTC-4, wrote:
Does anyone have schematics or suggestions for repairing a Tek P6563A scope probe? The problem is the signal line has only a 390 ohm resistance to the shield as measured with a DMM.

If you have a x1 probe and it's not connect to the scope (or any other piece of test equipment) then the resistance should be near infinity.


It is 20X, with the ID pin.


Then it must be 20 times infinity with the ID pin :-)
Mikek


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amdx wrote:

On 7/27/2014 5:17 PM, Michael A. Terrell wrote:

wrote:

On Tuesday, July 22, 2014 12:15:42 PM UTC-4, wrote:
Does anyone have schematics or suggestions for repairing a Tek P6563A scope probe? The problem is the signal line has only a 390 ohm resistance to the shield as measured with a DMM.

If you have a x1 probe and it's not connect to the scope (or any other piece of test equipment) then the resistance should be near infinity.


It is 20X, with the ID pin.


Then it must be 20 times infinity with the ID pin :-)


The ID pin changes the displayed gain. It is simply a resistor to
the shell, and the value is how the scope determines the attenuation.


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.