Re: Tektronix 2467B Auto Measure Faulty?

Chuck Harris
 

First thing you need to know is that the cursor measurements are
calibrated to be in the center of the noise on the trace, not on
the peak of the noise on the trace, so all of the 1.06V, or so
measurements you have made with the cursors are not being done
correctly.

There are two principle measurements done with the Parameteric
section: voltage measurements and time measurements.

Voltage measurements use the trigger set point on the hybrid to
measure the most positive voltage of the waveform, and the most
negative voltage of the waveform that they can trigger upon.
They take the difference to get the peak to peak voltage.

Time measurements use the trigger hybrid to trigger the A and B
sweeps to measure the center crossing of the first and second cycle
of the waveform, and then read the time between those two points.

Automatic setup uses all aspects of the measurement system to give
you a 1 cycle, or so, waveform that fits on the screen in amplitude.

The trigger hybrid is the center of both timing and voltage parametric
measurements. It must work for voltage measurements, or it will not
work for either voltage or timing measurements.

But, it can work for voltage measurements, and still not work for
timing.

And, it can work manually for all measurements, and not work at all
for parametric measurements... they use different control paths.

I find that contact problems on the contact pins of the trigger
hybrid socket are the number one problem. You can put in a dozen
new hybrids, but if the socket pin isn't making contact, in just
the right way, none of them will work reliably.

My suspicion is that the pad on one of the hybrid terminals is
done badly, and relies on the socket pin to touch it in just the
right place for it to work. More investigation is necessary.

DeOxit, and some wiping on the socket pins is often helpful.

The Parametric Measurement's PAL's socket is another trouble
area. It should be cleaned with DeOxit.

Now, on to the flowchart:

The first step asks if volts is accurate (must be timing measurement)

This wants you to set the measurement mode to measure volts on an
AC waveform.

If the volts measured is wrong, or simply goofy, then you need to
troubleshoot the trigger system.

If the volts is correctly being measured, then the problem could be
that the parametric measurements section needs to be calibrated.
(CAL01 and CAL09).

In my experience, that rarely, if ever, fixes the
voltage measurement.

-Chuck Harris


leandro.lindemann via Groups.Io wrote:

I'm trying to understand where to start looking for the defect and I really appreciate any help.

Checking the service manual, there is a defect flowchart. In the Parametric measuremet trobleshooting section I have the 1st doubt:

The first first question is:

Is volts Acurate? (Must be timing measurement)

If the answer is no, check triger system
If so, perform cal 01 and cal 09.

My doubt is, is the measure of time that needs to be checked measured by the Auto function or manually?

From the video, you can see that using the Auto option the displayed waveform is outside the time base, but without using the Auto function everything is normal.
Thanks.

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