Bad probe-what's wrong?

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

First thing to do is describe the experiment in enough detail to think about it. What model probe master? link to specs?

Divisions??? Frequencies are important. Sweep rate? Not at all clear what you mean by separated by divisions and up and down from center. Are you saying that the DC levels using the good probe are not centered around ground but the bad probe is? AC coupled looking?

What do you measure OHMS from the tip of the probe to ground with the probe connected to the scope with the input set to DC? What OHMS do you measure across the BNC with the tip shorted? Tip Open?

Can you get the BNC end apart to measure the cable resistance?

TEK scope probes had a resistive center conductor, but it wasn't a huge number relative to the input impedance. probe master is unknown.

I'm betting that you have an open connection or a fried resistor somewhere in the tip or compensation box.

If you know anybody with a TDR, they could make short work of it.

Check the 9Meg resistor in the tip. Depending on what's in the compensation box or whether the probe has selectable 1X 10X, you might be able to measure it without disassembly.

If you can disconnect the center conductor of the cable at both ends, measure the capacitance at each end. If not the same, the ratio of capacitances give some idea where the break might be.

What I mean is that if the wave was a proper shape there would be two horizontal lines 1.5 divisions apart. These lines have a shape that is a curve that starts fairly steep and then gets closer to flat. At the point where the curves are closest to flat I would expect to see 1.5 divisions separation. but it's more like 1/5 of a division. Eric

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

Sounds like it's AC coupled.

Hmm well I'm not much of a probe guy, but your probe has to be compensated for the input impedance (R and C) of the 'scope. It could be that the probe is not designed to work with the input of your scope. Is it a x10 probe?

George H.

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

GH

So if I guess correctly the probe is suffering poor hf response. Without any info from you on your test freq or the probe's specs what can one say? Some probes have very low f limits, and it varies greatly from x1 to x10.

NT

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

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

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

2. 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.

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

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

1. 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

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