I wish it were so simple as a ground lead. If you put the probe tip on the
scope calibration ground, it still oscillates. I tried all of the
combinations of direct leadless ground connections to the calibration and
scope ground I can think of, and it has no effect on the oscillation. I
also tried all eight inputs on my two scopes and cleaned the connections on
the scope with de-oxit compound. No effect.
Eventually I will cut into the probe tip and probably destroy it. Perhaps
if I knew how it was put together I could avoid destroying it. I suspect
that the Fet input transistor gets damaged in some probes which leads to
oscillation. The fact that I have two probes without the oscillation
means that it does not have to happen.
In any case, this probe is far far superior to my old P6201 probes.
Any chance you are interested in math and continued fractions? I have
some interesting unpublished formulae.
Jerry
On Mon, Aug 12, 2019 at 4:27 PM Lawrance A. Schneider <
llaassllaaass@...> wrote:
Hi,
Perchance a silly question, but as a fellow fizzilist, how long is the
ground lead? Maybe a resnoant problem?
On Aug 12, 2019, at 1:36 PM, wjlentz@... wrote:
4 P6249 probes passed through my hands that have 1 MHz oscillation. On
one probe, this oscillation only shows up after a 5 minute warmup. The
oscillation can be as large as 467 millivolts on one probe which makes it
mostly useless. On another probe the oscillation is smaller and
manageable. The probes that have oscillation meet rise-time specs and
have no dc offset. I have one very expensive P6249 probe that has no hint
of oscillation.
I have two TDS 694C 3 GHz oscilloscopes and needed an active probe with
higher impedance than my 500 ohm passive probes. The TDS 694C is wired to
power the P6249 4 GHz probe with +/-5V and +/-15 supplies and a data and
clock pin interface to the TDAS694C.. I have the Tek manual which only
shows a block schematic for the part that connects at the oscilloscope but
not what is actually in the active probe tip. The oscillation shows up
on all eight of the inputs for the two TDS 694C scopes I have.
Is there any information about what is in the probe tip such as a
schematic? Is there any way to open the sealed probe tip? Would reducing
the +/- voltage to the probe tip at the scope connection, which can be
opened, help the problem?
All I hear from repair places is that they do not work on this probe.
Local sources of the probes are asking more for the probe than I paid for
my TDS 694C scopes.
I have the 1 GHz and 1.5 GHz versions of the probe which do not use the
+/- 15V supply and have no hint of oscillation, but I do need the bandwidth
for my photon counting business.
www.marinaphotonics.com.
I designed the PV16 1.5 GHz 65db gain amplifier discriminator for my
photon counter which is in a 29mm cube and does not oscillate, so I have
some knowledge of electronics. At this point I admit that I am just
stubborn and want to fix the probe problem rather than go to another probe.
Jerry the fizzilist
PS that's what happens to physicists when they get older
