gofar99 Messages: 1903 Registered: May 2010 Location: Southern Arizona
Illuminati (5th Degree)
Hi Everyone &^%$##@!. Last night I found a new way to fry a PC based digital storage scope. This BTW is my second one. Not all DSOs have their inputs protected from voltage overload. In this case the Velleman 1000 didn't. I really like the software it uses and they way it does measurements. Unfortunately the voltage input is limited to 30 volts (300 with the 10X probe). The first one died about two years ago on an AC mains ground fault. I sent it to the company to see if it could be serviced....they said I fried nearly everything and it would be far cheaper to get a new one. $%#*&^%.... OK about $350 down the tubes. Last night I was doing some measurements on a phono preamp for noise levels. When the stuff I am testing for is at -85 to -90 dbv the scope needs to be on the lowest range (5mv/div). A small blob of solder that some how managed to remain in the case shifted. It went between the B+ and the tube side of the output coupling capacitor (a hefty 1.0uf poly). The spike into the cap was probably about 200 volts. Bingo out goes the DSO. Now I'm trying to figure out how to replace it and at the same time protect the new one without compromising the precision of the measurements.
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Last night I found a new way to fry a PC based digital storage scope. This BTW is my second one. Not all DSOs have their inputs protected from voltage overload. In this case the Velleman 1000 didn't. I really like the software it uses and they way it does measurements. Unfortunately the voltage input is limited to 30 volts (300 with the 10X probe). The first one died about two years ago on an AC mains ground fault. I sent it to the company to see if it could be serviced....they said I fried nearly everything and it would be far cheaper to get a new one. $%#*&^%.... OK about $350 down the tubes. Last night I was doing some measurements on a phono preamp for noise levels. When the stuff I am testing for is at -85 to -90 dbv the scope needs to be on the lowest range (5mv/div). A small blob of solder that some how managed to remain in the case shifted. It went between the B+ and the tube side of the output coupling capacitor (a hefty 1.0uf poly). The spike into the cap was probably about 200 volts. Bingo out goes the DSO. Now I'm trying to figure out how to replace it and at the same time protect the new one without compromising the precision of the measurements. 
