Insulator/shielding in DEC power supply - test-drb@ccmp.vtda.org

2 Sep 2008

Ian King said:
...
  I'm reconditioning some H7100A power supply units
in a VAX-11/785, and
 I've come across something I haven't seen before.  I'm hoping one of you
 has.   :)

 This particular PSU was labeled 'Memory Power Supply' and has additional
 regulator boards for a 15v rail.  Slipped between those boards were two
 sheets of what looked like heavy-duty paper.  However, one had
 delaminated, demonstrating that it is a sheet of thin copper sandwiched
 between two paper-like layers.  That suggests to me that this was  intended
...
  more for EMI shielding than electrical isolation.  I
did not see  these sheets in
...
  another PSU that also had a supplemental regulator.

 Does this sound familiar to anyone?  TIA - Ian 

In my VAX 11/750[1], each of two power supplies
(2.5v and 5v) also contain this 'heavy' paper
separator between adjacent boards.  I've noticed
that this paper is pretty thick, not quite what
you'd call cardstock, but getting close.  In my
case, I haven't noticed any de-laminating, so can't
confirm the copper foil inside, however, I have
commented to myself a time or two that each sheet
just 'feels' heavy.  If there really is foil inside,
I don't know how much EMI suppression it would do,
since there is no connection of ground or other way
to bleed of any incident energy.  Rather, I'd guess
they probably make pretty good reflectors of EMI,
instead.  But what do I know, I'm hardly a hardware
guy.

- Jared

[1] Was brainless when picked up almost a year ago,
but I've since gathered a set of all of the CPU boards,
memory and other necessaries. Just picked up a DEUNA,
but still need the cab-kit for it.  Fixed the faulty 5V
power supply, but now the 2.5V PS is goofy; presently
working on that.  At this rate, I'm now hoping to fire
the whole system up for the first time, sometime before,
oh, I don't know, maybe before Christmas?! :)