PDP 11 gear finally moved

Mark J. Blair nf6x at nf6x.net
Mon Jul 20 09:49:09 CDT 2015

If I may go back to the original post topic for a moment, what model is that line printer that is pictured? I'm on the lookout for a DEC LP32 to go with my 11/730.

Now on the topic of capacitors: The only component type that I replace on sight at this point are the Rifa paper-dielectric EMI suppression caps. Had one go incendiary on me so far, and I do a replace-on-sight routine on them because my hypothesis of the failure mechanism(*) leads me to believe that they're all likely to burn up once the plastic shell has developed any cracks. They're easy to recognize: Rectangular, with transparent yellow plastic housings, which are usually crazed with fine cracks. Different caps which should not be subject to the same failure mechanism are easily available.

(*) Paper dielectric is said to absorb moisture from the atmosphere if not sealed. So, I presume that once the yellow plastic shell cracks from old age, moisture gets in, and then the caps break down under power. I replace these with poly film safety-rated caps with suitable ratings, since the poly film shouldn't absorb significant moisture even if the housing seal fails.

Mark J. Blair, NF6X <nf6x at nf6x.net>

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