Recently my scope and I had an unfortunate encounter with some high voltage and it left me with one channel out. I am slowly working through the process to see if I can fix the scope. I will blog about my journey at a later date whether I can fix it or not. Among the damage the high voltage caused was the loss of the 1X circuit in the probe cord set.
This is an inexpensive 80 MHz Hantek probe and after the high voltage experience the 1X 10X switch had no effect. My first thought was to junk the probe and see if I could use the wire with the BNC connector for another purpose. The probe itself looked like it was molded in plastic and as I sat trying to decide how to cut it apart I noticed that the strain relief on the wire would slide off the handpiece. Next I noticed that the plastic handpiece would also slide off the internal barrel. Little by little with lots of pulling and I admit even some prying I got the handpiece apart.
So far everything that I had done to the handpiece was reversible. I measured all the components and the only problem was the little switch itself.
When examined closely the switch looked like it could be disassembled by opening a metal cover clip. I removed the clip and took out the white plastic slide with the metal contact fingers. Looking inside the switch I could see the black burn caused by a high voltage electric arc.
It is hard to see the burn spot inside the switch but it is on the left side. I cleaned the wiper contacts and the contacts inside the switch body using a little De-ox-id on some paper towel bits. The switch snapped back together and worked like new. The metal sheath that covers the circuit board and carries the ground forward to the alligator clip was a little loose when pushed back together as it was not designed to be repaired so I had to use a sharp center punch to make it tight. The plastic pieces all slid back into place and when fully reassembled the probe worked just like new.
It was fun to see what was inside an oscilloscope probe and it was even more fun to fix something that was never designed to be fixed.
John
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