[time-nuts] aging/failure of un-powered xtal oscillators?

paul swed paulswedb at gmail.com
Fri May 17 09:06:14 EDT 2013

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
My actual concern would be the dram technology at that age simply various
breakdowns that might be occurring creating unreliable memory.

On Fri, May 17, 2013 at 8:07 AM, Grant Hodgson <grant at ghengineering.co.uk>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
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