Re: 7854 revived with a new CRT - how to correctly calibrate Z circuit (was: #157693 - https://groups.io/g/TekScopes/message/157693)


unclebanjoman
 

Hi Dan,
thanks for your explanations. Very clear and concise.

I've rechecked carefully the adjustments of R135 and finally I adjusted the baseline to 10 V.
Regarding the GSF, I readjusted to get TP103 40 mV less than the voltage on TP122.
Varying the A and B INTEN controls through their range shows stable TTL pulses between -0.2 V and +2.4 V, so I can assume that the Z section is perfectly calibrated, disregarding the strange behavior when switching to A timebase that you confirmed.

Now I'm facing with another problem: since I changed the CRT,I had to recalibrate all the vertical and horizontal offset, gain etc. in the analog section.
I used the 067-0587 standardizer. All things goes o.k.

Then I made some measurements using the digitizer part.
It turned out that the digitized waveforms had wrong amplitude (and some offset) compared with the real waveform (using BOTH command to view the acquired and real waveform).
So I managed to quicky recalibrate the vertical pickoff system, precisely the vertical sampler offset (A25R380) and vertical sampler gain (A25R290).

Now the digitized waveforms looks o.k. in amplitude and step response, but they are wrong in horizontal scale.
Superimposing the real and digitized waveforms the latter is more expanded than the former (shows an error of almost 0.8 div over the complete 10 div of graticule).
Moreover, I noticed that the first acquired points seems not filled (shows a perfect flat line).
I assume that surely the horizondal must be recalibrated also.
Should I perform all the tedious steps in the H section of the service manual, starting from H1 and up to H6 in strict sequence, or is there a more quickly procedure?

Thanks again for your advice and observations, Dan.

Max

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