[R-390] Megger and Capacitor Measures ... Good vs. Bad ?

[Alan Victor]

 I have been playing with a 500V Megger looking at questionable capacitors
in the R-390A. Somewhat of a challenge to determine is this really a bad
cap or borderline ok. After looking at a few known good caps, it became
apparent that a baseline for good versus bad would be useful. As it turns
out, this work was already done very nicely back in 1955 by a couple of
folks at the Diamond Ordnance Fuze Labs in Washington, DC. They plot the
MEGOHM x MICROFARD product for a variety of caps from the time, namely
mica, ceramic, paper, glass, and some poly plastics. At room temp, all of
these caps fall in the range of 4-6.2 (meg x uf ) product! Hence, a 47 uF
looks like about 100k ohm while a .01 uF should look like 400 -500 meg ohms
(infinity!).  Handy to know and this is about what I saw on the Megger.
Their applied V is in this work was ~ 200 V. Curious if any of the folks on
the list have established a neat pass-fail criteria.
Alan W4AMV