Hi If you dig into the modern GPS Rb’s they put the 5065 to shame. They are also don’t seem to show up on eBay ….
Bob > On Mar 12, 2016, at 4:50 PM, Bruce Griffiths <[email protected]> > wrote: > > The ultimate solution to this conundrum is to roll ones own Rubidium standard > to achieve performance beyond the HP5065A e.g.: > https://doc.rero.ch/record/32317/files/00002318.pdf > > Bruce > > On Saturday, March 12, 2016 01:46:29 PM Bob Camp wrote: >> Hi >> >> Another example of the “stored in magic memory” issues on some modern Rb’s: >> >> To improve the yield of Rb’s cells, a DDS can be used to tune a bit one way >> or the other off of the normal resonance frequency. The reasons why they >> are off are a bit involved, the fact is they do get manufactured that way. >> To line things up with these cells, some sort of coarse tune word is dumped >> into the flash / eprom / whatever. That DDS now knows where to find the >> resonance of the cell and it has. This all works fine until you swap a cell >> between boards. The new cell may (or may not) line up with the old cell. >> Things may (or may not) lock up properly. >> >> Once you get past the “blown capacitor”, “no output on the regulator” or >> “dead power transistor” sort of fixes …. the newer Rb’s are not >> particularly easy to care for and feed. Indeed, the Temex units I mentioned >> earlier probably all could be fixed with detailed work and access to the >> code. I stop when the simple “replace these 4 caps” stuff does not bring >> them to life. As long as that gets more than 60% running, I’m happy. >> >> Bob >> >>> On Mar 12, 2016, at 12:14 PM, [email protected] wrote: >>> >>> Mike, >>> >>> If you are planning to buy "suspect units" with the intent to repair I >>> would steer clear of the PRS10. >>> >>> It is true you can pay for a factory repair but having the schematics and >>> theory of operation only helps for particular repairs. >>> >>> This is because a lot of the alignment parameters are stored in memory >>> and there are no instructions on these alignments and how to store them. >>> >>> An example: I had a unit come in for repair. It had no output. The >>> customer, a professor, said a student applied a large DC to the output. >>> The output is direct from an RF transformer. It burnt open the winding. >>> >>> I thought, how hard can it be? >>> >>> I popped off a good output board from a junker and installed it. I now >>> had an output but the unit would not operate properly. Part of the output >>> go to other circuitry that would need to be aligned to match. No way to >>> do that or store the alignment! Bummer. >>> >>> Luckily the transformer was a metal can type. I opened it up and rewound >>> the tiny wire output coil and that restored the unit to operation. >>> >>> After that I sold my pile of defunct PRS10 units and don't plan to >>> purchase any more. >>> >>> For ease of repair the HP 5065A is first, then the FRKL and H, these have >>> bog standard thru hole circuitry and the manuals are excellent. Another >>> of the worst is the M100 as its cards are conformal coated and the lamp >>> oven assy. is potted! As you mentioned most of the later telecomm units >>> are surface mount and most have some sort of microprocessor involved. >>> >>> Cheers, >>> >>> Corby >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the >>> instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the >> instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
