Hi The DRAM's (and some cpu's) of that era were not as well specified for clock timing as the parts we have today. It's a matter of degree, but it was much worse back then. I would worry less about frequency than about duty cycle. In this case with a binary divide, the duty cycle on the clock should have held up pretty well. Who knows how well the DRAM chips have held up.
Bob On May 17, 2013, at 9:06 AM, paul swed <[email protected]> wrote: > Grant on the purest of speculation. Most likely not. Yes the xtal ages but > as you say the frequency is not critical. Though that actually may not be a > true statement. How far is to far for the dram timing? The other thing that > most likely is not an issue is a variable cap. Most likely it never had > one. At this age I have seen resistors change value. > I am confused are the boards really 25 years or are they 1980 at 30 plus > years. > My actual concern would be the dram technology at that age simply various > breakdowns that might be occurring creating unreliable memory. > Regards > Paul > WB8TSL > > > On Fri, May 17, 2013 at 8:07 AM, 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<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.
