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Those CDEs don't fail in conduction often. A whole string never seems to
go out at once either. Always one cap at a time for me. The string would
become a higher value cap at a lower voltage if that happened, so the
gap would still bang hard. Since his gap is acting like it has no caps,
seems like one went to high impedance. If a single string goes high
impedance, the overall MMC becomes a lower cap value, so that also
sounds like more or less what he is seeing.
On 3/10/2018 10:50 AM, jimlux wrote:
Talking about MMCs and potential failures brings up an interesting
question of "how do you find out which one is dead" (assuming you
didn't kill the entire string)..
Obviously, if one of the caps reads shorted with a ohmmeter it's dead.
But I suspect that you can have a "fails only with HV" sort of thing.
I wonder if setting up a test rig that puts 120 or 240V across the cap
would give useful information - that's still low enough that I'd feel
comfortable probing with handheld probes.
Does anyone who's had dead MMC have any insight into the failure
manifestation?