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I am wondering if it's safe to replace the BNC input connectors on my old Hitachi v-422 scope.

As long as I'm careful and stay away from the CRT etc? Or is there anything else I'm not aware of?

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What are you worried about? – tyblu May 3 '12 at 3:32
Carelessly dropping a hammer on the CRT may implode it, working with it on may kill you, so don't do either. – Kenny Robinson May 3 '12 at 5:13
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Why do you want to replace them? BNC are reasonable connectors for scope inputs. Every scope I've seen uses them. If you want something else, it would be better to make adapters that plug onto the existing BNC connectors than to mutilate your scope. – Olin Lathrop May 3 '12 at 13:00
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Olin: perhaps OP means replace the original ones with a duplicate replacement due to damage... we had a Lecroy scope a number of years ago that had one sheared off from an "incident". – Jason S May 8 '12 at 23:57
@Jason: As you say, perhaps. The point is we shouldn't have to guess. Since this OP is refusing to answer questions, all that's left to do is close the question. – Olin Lathrop May 9 '12 at 15:14

2 Answers

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There is nothing inherently unsafe about what you're proposing. The only significant safety risk associated with this undertaking is the presence of a CRT and potentially large capacitors. Please note that standard cautions apply regarding these and you should look up informative instructions in advance of attempting your modification. A few points though from a practical standpoint rather than safety:

  • The BNC connectors on the scope are normal but I am assuming they have broken or something and this is driving your desire to replace them.
  • There may be an implication for signal quality with whatever you replace them with (stick with shielded cables if possible). Recalibrate the scope if possible (usually a clip on the front).
  • Cable stress.
  • Assembly/disassembly difficulty.
  • Don't break anything because you may not be able to find parts easily.

If you are still uncomfortable with the concept, imagine you are repairing the connections on the back of a TV--what would you be worried about there? The answer is a CRT and large capacitors (the same stuff). And someone in the room juggling hammers, burning yourself with a soldering iron, etc.

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Yes It is safe to replace the BNC input connectors on your old Hitachi v-422 scope, as long as you observe the zones starting from the AC input to the high voltage DC outputs to the CRT grid and CRT flyback transformer, it is ok.

Keep in mind arcing occurs in air around 1kV/mm or 25kV per inch, so 2" keep away is a good rule of thumb for these High voltage heavy insulated wires. Plastic and PVC is usually 5kV/mm and dust/dirt can degrade that, such as your car distributor. Flyback doubler caps can hold their values for a long time even with power off, so TV repair techs would discharge before replace them. But if you understand the physics of dielectric breakdown and insulation resistance, and take care, IT IS VERY SAFE to CHANGE YOUR BNC front panel connectors. Old TV techs "kept one hand in their pocket" or floating just in case they were careless when poking around near high voltages to avoid cardiac current loop.

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