Theory of relativity visits real-time clock

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It didn’t help, though. All the applications still failed tostart. Just to make sure I hadn’t missed something in theclock-setting procedure, I did it again. Nothing changed in theapplication’s behavior, but I noticed something strange tosay the least: The clock ran much faster than its normal speed eachtime I started the time-setting utility. It came to its normalspeed when I entered the correct date and time settings, however.So, it probably had a good reason to come back to its higher speedbecause, the next time I entered the time-setting utility, it wasagain speeding up. Turning the instrument off for a longer periodwas helpful: The next time I turned it on, I saw a noticeableadvance in its clock. The clock sped up immediately afterpower-down.
My next test was simple: I performed all the same steps except forpower cycling, ignoring the advice in the manual. Everything workedfine, and the picture became clear. Lowering the supply voltage ofthe CMOS inverter in the 32,768-Hz clock oscillator causes highergain but longer gate delay. Now, it was possible to more easilysatisfy the phase- and magnitude-balance conditions for the thirdor fifth overtone than for the crystal-fundamental tone. I sawsimilar problems when trying to build a crystal oscillator based ona CD4000 series XOR gate connected as an inverter. Once it entersthis mode, the oscillator stays in it, even when its supply voltageramps up to its nominal value. Only writing a new time setting atnominal supply voltage can turn the oscillator back to itscrystal-fundamental frequency. Possibly, it disables and thenre-enables the oscillator when accessing internal chip registers.
The next day, I got a replacement battery and put it into theinstrument. Just in case someone might have the same problem, Isent a short e-mail describing it to Tektronix support. From thisexperience, I learned a principle of relativity: You may have anapplication time out not only because the application is too slow,but also because your real-time clock is too fast!