Re: Calibrate the time base, or horizontal amplifier?


Here is how I did the calibration without time mark generator.

Using a 5B10B time base and a 5A14N vertical module in slot #1.

The +30V has a very small tolerance, which I used to calibrate the scope calibrator output. So I set the +30V until I had exactly 400mV on the calibrator, and the 30V was still within calibration. 400mV measured with an Agilent 34401A. Then I set the -30V to exactly the same level. So +30 and -30 are nicely balanced.

Make the calibration signal visible with 4 divisions vertical.

The sensitivity at the backplane is 50mV/cm. I soldered two wires on the PCB of the 5A14N, which lead to pins 7A and 7B. I hooked those up to the Agilent 34401A. Connect the calibrator to the vertical module input, and use the "Cal" potmeter to adjust the backplane signal to exactly 200mV. So 4 divisions on the screen. Do not touch this potmeter setting. Any deviation is now caused by the vertical amp. Adjust the vertical gain for 4 divisions.

The next step is a bit strange, but the manual sais so too.

Swap the time base module and the vertical amp.
This rotates what you see on the CRT by 90°. The vertical amp output which has a known 200mV still, is now in the time base slot (#3). This 200mV drives the horizontal amp. Adjust it for 4 divisions.

So now the vertical and horizontal amp are cablibrated.

Put back the time base and the vertical amp in the normal slots, and make the calibration signal visible. Any error is now caused by the time base being too slow or too fast. The calibration signal is not 50% duty cycle nicely. So I used a digital controlled oscillor and set it for 10kHz square wave. Now adjust the timebase to 10kHz is displayed correct.

That's it. A bit unconventional, and I hope there is no mistake in the system, but it worked very good.

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