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 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

GandalfG8@aol.com wrote: > 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. Interesting. There's what, nearly half a dozen reported failures now? - 2 of yours - 1 of mine - and someone else who emailed me the other day about possible alternatives to the Schaffner filter unit It is, in all likelihood the X2-rated mains filter cap that's blowing -- I've seen a similar fault on BBC Micros when the X2 caps fail in those, which causes the same brown smoke emission. In those, however, the smoke doesn't usually condense and stick... I suspect if I ever get another 7150+, I'll be swapping the line filter on the instrument's arrival... -- Phil. lists@philpem.me.uk http://www.philpem.me.uk/