HP 3562A "non-real time clock" function? - Page 1
Forum section: electronics / testgear

author: aarons
author_rank: Regular Contributor
timestamp: July 07, 2025, 07:09:05 pm
content: This analyzer has a "non-real time clock" that stores the time and date. According to the manual this is used for time stamps if you have a disk storage GPIB thing, and for automatically starting auto sequences at specific times. I'm not really looking to do either of those, but I'm bothered by an incorrect clock so I set it.Today I noticed it was wrong again. After some experiments I discovered that while the time and date is saved in nonvolatile memory, it doesn't advance when the analyzer is off. Is that really how this clock is designed to function, or is mine broken?

author: edpalmer42
author_rank: Super Contributor
timestamp: July 07, 2025, 08:37:26 pm
content: Does it have an internal (probably on-board) battery that's on its last legs? Either a soldered-in lithium battery or a Dallas Semiconductor memory/battery unit. I can believe that a battery could be too low to run the oscillator, but could still power the RAM.There might be a diagnostic check for the battery.

author: aarons
author_rank: Regular Contributor
timestamp: July 07, 2025, 09:49:33 pm
content: It does have a battery, and I replaced it when I got the unit a month ago, so I don't think that's likely but I'm going to dig around in the service manuals to see.

author: edpalmer42
author_rank: Super Contributor
timestamp: July 07, 2025, 11:17:04 pm
content: I have an HP 8647A signal generator that has an internal lithium battery. Something went bad in that circuit and now it drains the battery quickly. You might want to check yours again to make sure something similar hasn't happened. Did you check the new battery voltageafteryou replaced the old battery?

author: wn1fju
author_rank: Frequent Contributor
timestamp: July 08, 2025, 11:51:34 am
content: My 3562A works the same way as yours. The clock is updated while the thing is running, but when you power the unit down, it only saves the last clock time to memory. The next time you power the unit up, the clock starts again from that last saved time.I have never had an occasion to use the date/time functions, but it does seem a bit dumb.

author: Peabody
author_rank: Super Contributor
timestamp: July 08, 2025, 02:27:57 pm
content: Quote from: wn1fju on July 08, 2025, 11:51:34 amThen what would the battery be for? Is it just to preserve the memory?The DS3231 RTC has a bit in its control register that determines whether the oscillator continues to run when on battery power, which I've always assumed was so they could install the battery in a new part, but not draw any current when on the shelf or during shipping. Could there be something similar in this case?

author: wn1fju
author_rank: Frequent Contributor
timestamp: July 08, 2025, 05:44:35 pm
content: "Then what would the battery be for? Is it just to preserve the memory?"Apparently yes since the 3562A can store states, traces, configurations, etc. The one thing it can't seem to do is update the clock while it is off. I don't have a complete set of schematics for the processor board, but a quick glance at the parts list didn't show any kind of RTC chip (unless I missed something).HP is quite convincing in their 3562A user manual where they refer to the date and time front panel menu selections: "used to enter the date (time) of the non-real time clock."I think the term, "non-real time clock" is your first clue!

author: aarons
author_rank: Regular Contributor
timestamp: July 09, 2025, 12:30:31 am
content: That term is confusing, since when the analyzer is running it is a good approximation of a real time clock.