[Test-Equipment] Solartron 7150plus DMM Failure

[John YAHOO]

> 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
> meter.
>
> 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.
>
> regards
>
> Nigel
> GM8PZR


Nigel,
I had the same thing on a Racal meter.  It was either a 5002 or a 9303 with
the same Schaffner filtered mains socket.  A terrible smell, some smoke but
it continued working.  I wanted to use the meter urgently and didn't have a
spare filtered mains socket.  The mains filter components are moulded into
the rear of the socket.  I got a small hack saw blade and carefully cut
around the moulding removing all of the mains filter components but leaving
the original thick mains bus bar connections in place.  I shortened these
and reconnected the internal mains wiring.  Its still working fine.

John G3UGY