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amdx[_3_]

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