[time-nuts] [OT] Re: Solartron 7150plus DMM Failure

GandalfG8 at aol.com GandalfG8 at aol.com
Tue Sep 22 10:44:24 UTC 2009

In a message dated 22/09/2009 11:16:03 GMT Daylight Time,  
robert8rpi at yahoo.co.uk writes:

The  filter is an FN372 2A unit. This is a common failure. It's due to the  
particular type of epoxy cased, self-healing capacitor used in the filter. 
The  case encapsulation cracks and if the unit is left in storage damp gets 
in. The  self healing is by the metal coating that forms the capacitor 
plates  vaporising when the insulation breaks down. Evenventually this forms a 
sort of  chain reaction and the whole thing goes up in acrid smoke. It's not 
related to  any MIL spec. The capacitors are used in some Farnell 
powersupplies and are a  common failure there as well. Equipment that is in regular use 
seems to be OK,  leave it in the garage for a year and you may have 
trouble. The problem with  the FN372 is that it's a snap fit and has the voltage 
selector built in. There  is no direct fit alternative that I know of. New 
FN372's (with better  capacitors) are available from RS for under £30. 

Hi Robert
Thanks for the information.
I wasn't thinking it was anything to to do with a MIL spec, pretty sure  
these are standard Solartron spec anyway, but just commented on it being  
ex-mil as many have come on to the UK market as military surplus.
However, your comments on storage suggest that origin might be  more 
relevant than I appreciated.
My three units have all been kept warm and dry here but there's no  telling 
how they might have been stored in the run up to, and  following, disposal, 
I've seen plenty of previous examples of  ex-mil kit that has suffered from 
poor storage conditions.
When I have more time I will see if I can rebuild one of the blown filters, 
 although these are quite nice meters I'm still reluctant to spend around 
£90  on replacement mains connectors.
I agree it's the snap in issue that makes it much more awkward  but I'm 
considering the possibility of fitting an adaptor plate to  accomodate a screw 
fixing connector/filter, or even an alternative snap  in.
Doing away with the voltage selection option is another possibility that  
might generate more space to work in.

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