I'm just looking at an electric fencer output board at the moment, it's not plugged into the fencer, I'm just testing the components are it has a fault. I'm having trouble with these here though, they read ol for resistance, no capacitance, nothing in diode mode, so scratching my head on what on earth they are, as they have no kind of marking either. They just have a white end, and straw coloured other end, but seem to have no electrical properties according to my multimeter, so not sure if they are just damaged or what.

enter image description here

Edit Here is the circuit enter image description here

  • \$\begingroup\$ Maybe (polarized?) spark gaps? \$\endgroup\$ Apr 11, 2016 at 19:15
  • \$\begingroup\$ A (partly) schematic may be useful to identify their purpose \$\endgroup\$
    – PlasmaHH
    Apr 11, 2016 at 19:16
  • \$\begingroup\$ Also note that those neon lamps (the two glass packages, assume they are neon lamps, could be some specialty discharge tube) seem heavily oxidized. They may have failed, as a result of, or contributing to, other failures. \$\endgroup\$
    – rdtsc
    Apr 11, 2016 at 19:29
  • \$\begingroup\$ This has the same items: ozvalveamps.org/repairs/fencer.htm , haven't figured out what they are. \$\endgroup\$ Apr 11, 2016 at 19:57
  • \$\begingroup\$ Iv added a diagram now \$\endgroup\$ Apr 11, 2016 at 20:13

2 Answers 2


Some guys ask themself the same question: http://www.anotherpower.com/board/index.php?topic=908.0 and they have come to conclusion that those are VDRs.

  • \$\begingroup\$ Looks like they were talking about the blue capacitor in that thread as I see nothing about the cylinders. \$\endgroup\$ Apr 12, 2016 at 8:50
  • \$\begingroup\$ @IainSimpson Citations: "One thing that puzzles me in the URL is the photograph showing what appear to be 14 pieces of a ‘cream and white’ things that protect the neon bulbs. That is seven pieces on Full Power, and another seven on Half Power. Can anyone explain what these are?" "I believe the things you are describing are in fact the VDRs. 7 in parallel on the "low side", 7 in parallel on the "high side", and thus forming a divider to provide the "middle" (lower output)." Photo: ozvalveamps.org/repairs/fencer.htm \$\endgroup\$ Apr 12, 2016 at 9:17
  • \$\begingroup\$ @IainSimpson That blue capacitors are actualy MOVs (VDRs). It seems they have found a replacement for those old parts, they say MOV 900VDC. \$\endgroup\$ Apr 12, 2016 at 9:24

I'd guess they're high-voltage diodes.
The ones I've used in the past had such a high forward-biased voltage (about 10v) that the diode test function on a multimeter doesn't recognize them, but considering that their reverse voltage was in the 10-15kV range and they were only used for about 5mA forward current they were acceptable.

  • \$\begingroup\$ Iv added a diagram now \$\endgroup\$ Apr 11, 2016 at 20:13

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