[time-nuts] Solartron 7150plus DMM Failure

GandalfG8 at aol.com GandalfG8 at aol.com
Mon Sep 21 13:57:51 UTC 2009

Hi All
Apologies to any who may receive multiple copies of this but I thought  it 
worth sending to those lists where I've previously seen mention of this  
I have now had two identical failures of Schaffner filtered mains  sockets 
on ex-mil 7150plus DMMs, although I'm not suggesting the ex-mil  source is 
particularly relevant.
In both cases there has been an internal component failure within the mains 
 socket that caused it to emit smoke around the edges of the metal filter  
cover, accompanied by a brown goo and a very unpleasant smell.
The brown goo is deposited inside the meter in the area of the filter,  and 
very messy it is too, with a small amount seemingly contained within  the 
smoke and splattering on adjacent external surfaces.
In neither case did the meter stop working, or even pause to cough:-), so  
I'm assuming it's most likely to be the parallel capacitor directly across 
the  line input that's failed. According to the Schaffner schematic there's 
no  varistor in there, which might have been a preferred suspect, but there 
are two  series inductors followed by two more capcitors, one between each 
power  line and ground.
After the failure the meter can continue to be used as it stands  but 
really needs a strip down and good internal clean in the area of the  mains 
socket, and even then it's still likely to smell unpleasant.
I don't have time at the moment but will open up the filters  eventually 
and see what might be done to rebuild or just bypass them.
Just cleaning the filter internally too would probably help  reduce the 
lingering smell.
As a general precaution I would suggest, at the very least, standing these  
meters on a sheet of plastic and, if there's anything reasonably close 
behind  it, wall etc, folding the plastic up behind it too as extra protection.
The unit that failed here today was sitting on the top shelf of a test  
bench with its back fairly close to the wall, the wall is looking  better after 
a good clean but is still not very pretty!
A longer term fix might be to remove the filter components entirely and use 
 an external inline filter if required, there isn't much spare room inside 
the  unit so I don't think an internal stand alone would be an  option.

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