EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: solder_boy132 on December 19, 2020, 08:05:10 pm
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Recently bought my first oscilloscope from ebay. Its a tektronix 2235. 100MHz. It functions well. It seems healthy. When i fed in a square wave, it looked fine. But the gain was a little bit off. Time base as well. I asked Tektronix for the service manual and kindly did. I looked through and couldn't find how. Im familiar to high voltage CRTs so no worries on opening it up. Pls help. I Checked the CRT voltage and the meter went :bullshit:
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I Checked the CRT voltage
The 2235 is not digital. You have to use an analog meter.
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How are you measuring the gain?
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I did. use an analog. Set voltage setting wrong.
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Well thats what im guessing.
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Well thats what im guessing.
You say you have 'experience' with CRTs yet you aren't aware that there are thousands of volts behind that shield and over 10KV at the anode. On the off chance that you are serious here, the various adjustments required to calibrate the scope are scattered all around inside with most of them on the attentuator (input) board. How to adjust them is found in Section 5 of the service manual. Leave the high voltage shield in place unless there is a problem. The issues you are reporting have nothing to do with the CRT HV circuits. In case you didn't get a service manual, it is here:
https://w140.com/tekwiki/images/3/30/070-4206-00_2235_Service_Manual.pdf
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At the least, a working tektronix 067-508 amplitude calibrator and time marker generator 184.
These could likely be substituted with a calibrated DVM, frequency counter and square wave oscillator.
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Vertical calibration can be done with a function generator, AC voltmeter, and RF attenuator to make calibrated precision square waves. Complete horizontal calibration requires an RF signal generator or at least square waves up to 20 or 50 MHz, but rough calibration can be done with lower frequencies.
Before messing with the calibration, verify how far out of calibration it is.