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.
