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Re: 2465 Calibration
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Calibrating the 2400 Series Oscilloscopes is a manual, tedious process. It can be very frustrating especially if you don't have the equipment called out in the Calibration Procedure. It is written around using their equipment. It can also be frustrating if your Tektronix equipment isn't operating correctly. My PG506 out of the blue, started producing the wrong Voltages (15% low), with high ripple on the 50mV down requested Voltages. Luckily, I had my spare, but spent a couple of hours having the same Limit errors on CAL 02 Vertical Calibrations too. Turned out to be a dirty slide switch inside the PG506 that allows you to select DC Level/Square Wave for the Output. Easy fix of course. No one tells you that when they say "signal" they mean the Square Wave not the DC Level Output. My point is, these are automated tests expected to be performed with their designated equipment. It is hard enough to do the 2+ hour procedure with their equipment, let alone something else. Those who can do this in their sleep have my respect. Hang in there, you only have to get it right once in 30+ years - assuming that you rebuilt the Power Supply. By the way talking about Power Supply rebuild... I ran into 2 Bad 250uF 20V Capacitors in a 2465 CTS two days ago. These were the hermetically sealed ones that can fail. When looking near the bottom of the Capacitor package near the leads, a brownish electrolyte discoloration was visible. When I removed the components, they tested around 56nF and a noticeable black soot was seen around the pins at the base of the Red Hermetic Seal. The pins were also loose in the Hermetic material. Others I removed with similar characteristics and tested, they looked okay, but I replaced them as well as a preventive measure. Ross -----Original Message-----
From: [email protected] <[email protected]> On Behalf Of si_emi_01 Sent: Friday, April 29, 2022 4:24 PM To: [email protected] Subject: Re: [TekScopes] 2465 Calibration Comments below: Ross -----Original Message----- From: [email protected] <[email protected]> On Behalf Of jimbert4 via groups.io Sent: Friday, April 29, 2022 3:48 PM To: [email protected] Subject: Re: [TekScopes] 2465 Calibration Well I really messed up the vertical calibration today after getting limit errors on all the ranges. But I figured out the problem. My signal generator output was only 1/2 of what it was supposed to be. It's a Juntek PSG9080 that I bought on Amazon. It's supposed to have a 50 ohm output impedance and I discovered that when I connect it to a 50 ohm load (i.e. the oscilloscope) the output voltage is cut in half. Is that expected? I thought the 50 ohms on each end would be in parallel and not affect the output voltage. Ross - That is correct. If the source Impedance is 50 Ohms, when you load it with 50 Ohms, the voltage division node will be 1/2 of the voltage specified on the instrument. There is also a notification on the front of the Tektronix PG506 in Red that states the same condition. When doing the CAL 02 Vertical calibration, you are not doing that into a 50 Ohm Load, it is High Impedance. Also make sure that your Signal Generator is producing a Square Wave waveform with the requested Voltage Level being the High Level "Referenced to Ground". It can't be just a DC Level equivalent to the requested Voltage Level. Also verify that the Signal Generator does not have any ripple on the lower Voltage Levels. Any of these conditions will cause LIMIT errors and you won't complete calibration. Once again, using the Tektronix specified equipment is preferred. Also, using the PSG9080 is a pain in the neck because whenever I change the output voltage, I also have to change the offset to 1/2 of the new peak-peak to set the low end (approximately) at ground level. Ross - See above comment "Referenced to Ground" comment. How critical is the frequency used during the vertical calibration? I have seen both 1 KHz and 100 KHz mentioned as the frequency to use. How about 400 Hz? Then maybe I could use my DMM AC RMS meter with some conversion factor to get the peak value? Ross - I just measured mine and it is 1kHz for all of the requested Output Voltages of the PG506. They use other frequencies for the Fast Rise Waveform Tests the 1ookHz is used for that. |
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