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.