Usually aged crystals are reliable.
On Fri, May 17, 2013 at 2:07 PM, Grant Hodgson <[email protected]> wrote: > A client company has sourced a quantity of 'New in Box' iSBC series memory > modules manufactured by Intel in the 1980s for a MULTIBUS based computer > system. These are still in their original, sealed packaging and have been > stored (for 25 years) in controlled conditions. These cards are required as > part of a refresh programme for a mission-critical application (electricity > generation), which are currently using original Intel cards from the same > era. > > The memory cards use a 64.1kHz oscillator module as the refresh clock for > the DRAM. (I suspect that the oscillator module uses either a 2.5MHz or > more likely a 5MHz crystal whose output is divided down within the module by > 39 or 78 to 64.1kHz). > > As this oscillator is used only for DRAM refresh timing, the accuracy and > drift are not particularly important. However, reliability is important - > i.e. the oscillator must function, even if it is a few ppm off frequency. > > AS a matter of precaustion, all the tantalum and electrolytic capacitors on > the NIB cards are to be replaced as a matter of course, and any socketed ICs > will probably be removed, cleaned and replaced (to be decided). There are > several dozen cards to be replaced. > > There is an option to replace the crystal oscillator module, but it is > uncertain as to whether it makes sense to to the extra work. The > replacement oscisllator module will be from a different supplier to the one > Intel used, and would need some form of qualification. > > Is there a known failure mechanism whereby a cystal oscillator module that > has been sat on a shelf (as part of a complete card) in a benign environment > develops one or more characteristics that could impact it's reliability? > > regards > Grant > > _______________________________________________ > 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.
