Re: Tek 2467B

Michael A. Terrell

How many people would calibrate a scope, before verifying the scope didn't have bad caps? The S/H cap would be the least likely to fail, compared to the average lifetime of the electrolytics. Also, most of the scopes ending up in private hands haven't been in a cal lab for years or even decades so recapping the electrolytics would return it to the condition it should have been in at the last calibration. At least, anything I repaired would have been done this way.

Leakage around the S/H circuit's capacitor could be affected by contamination on the circuit board, as well. A good cleaning should always be part of testing and calibrating very high impedance circuits, as you well know. :)

I too, have worked in electronics for decades. Over five of them including at the factory on systems that were only allowed a 1.5 mV error in a system with a 0 to 5V output in a complex AGC circuit comprised of 14 Op-Amps. One of these boards was part of a kU band communications system for the International Space Station.

Michael A. Terrell

-----Original Message-----
From: Chuck Harris <cfharris@...>
Sent: Oct 15, 2018 8:40 AM
Subject: Re: [TekScopes] Tek 2467B

No, I said both could affect calibration. It all has to do with
what shape the scope was in for the previous calibration.

If the sample and hold cap was a bit leaky the last time it was
calibrated, replacing it with a good cap will restore its operation
and now the voltages it creates will be higher, thus invalidating
the last calibration.

Similarly, if a filter cap was letting through excess ripple during
the last calibration, the power supply settings would be incorporate
that ripple. Replace the capacitors and the excess ripple would be
gone, but the voltage will change by the average of the ripple.

It might not be a great affect, but it will be measurable.

These things are major repairs, and the manual is quite clear about
major repairs calling for a new calibration.

-Chuck Harris

Michael A. Terrell wrote:
Chuck said that the Sample & Hold capacitor could affect calibration, not electrolytics.

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