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

Grant Hodgson grant at ghengineering.co.uk
Fri May 17 08:07:20 EDT 2013

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?


More information about the time-nuts mailing list