Oscilloscope oscillation

[2deaf]

My Beckman 'scope went down after only thirty years of faithful service.  I knew it was coming, so I took the preemptive move of buying a new BK analog and a new Tektronix digital.  Both are just toys compared to the Beckman Industrial. 

Both of the toys send circuits into nasty oscillation that I am just not used to.  Anybody know anything about this?

[sluckey]

Could it be a probe problem?

[2deaf]

Could it be a probe problem?

That was my knee-jerk reaction and it could well be what is going on.  One of my Beckman probes went south many years ago and the remaining one had become erratic before the 'scope gave up altogether, so I don't have a for-sure good probe to compare the new ones to.  When the first Beckman probe failed, I was a little intimidated by the price of a replacement.  Even though I have a lot more money today, I'm still hesistant about buying an expensive probe when I don't really know if that is the problem.     


   

[sluckey]

Try just using a RG-58 BNC cable to connect the scope input directly to a sig gen output. And use a BNC Tee with a 50Ω terminator at the scope. (And if your sig gen has a 75Ω output, use RG-59 and a 75Ω terminator.) Do you get a clean scope display?

[shooter]

Could it be a probe problem

My HV probe did exactly what you're describing, was the probe, but I did spend a couple hours trying to "fix" the amp

[2deaf]

Try just using a RG-58 BNC cable to connect the scope input directly to a sig gen output. And use a BNC Tee with a 50Ω terminator at the scope. (And if your sig gen has a 75Ω output, use RG-59 and a 75Ω terminator.) Do you get a clean scope display?

I'm short BNC Tee's and Terminators right now.

I found a Probe Master probe on a Tektronix 454 that I had stashed away.  It has the compensation trimmer at the BNC connector end instead of in the probe housing and the cable is at least twice as thick as the stock Tektronix probes.  I put a Tektronix probe on the first channel of the digital 'scope and the Master Probe on the second channel with identical settings.  The Tektronix caused a circuit to oscillate and the Probe Master did not.  I'm thinking probe problem.

Thank you sluckey and shooter for your help.

   

[sluckey]

Does the probe really inject oscillations into the circuit? I've never had that problem with bad probes. But I've thrown away plenty of probes that simply showed oscillations on the scope display.

[2deaf]

Does the probe really inject oscillations into the circuit? I've never had that problem with bad probes. But I've thrown away plenty of probes that simply showed oscillations on the scope display.

That's a good point.  I just jumped to the conclusion that the circuits really were oscillating and didn't investigate it any further.

The consensus of opinion is that the probe is involved in the phenomenon and that gives me reason enough to order in some new probes.  Any suggestions on which probes are decent would be greatly appreciated.

Thanks.

[sluckey]

I like Tektronix P6100 series probes. Also like the HP 10070 family of probes. Lot of experience with these when working radar with FAA.