H7821 power supply in MicroVAX 3100, SCSI disk enclosures and others
Maciej W. Rozycki
macro at linux-mips.org
Sun Feb 16 18:06:09 CST 2020
On Fri, 31 Jan 2020, Peter Coghlan via cctalk wrote:
> If anyone has anything with H7821 power supplies in them, I suggest checking
> on these capacitors. If anything with these power supplies is in storage, I
> suggest ensuring it is stored the normal way up as this should limit the
> ability of the goo to escape and spread around the power supply.
Yep, known issue, discussed here and elsewhere several times previously,
with these Chemi-Con SXF caps, and also several other lines and reputable
brands of that era using a quarternary ammonium salt in the electrolyte
that breaks through the seal with time. Several DEC PSUs are affected.
Fortunately the H7821 is the least affected as long as the machine is
stored in the correct orientation (as you note) as the caps are facing
down then, meaning the salt does not interact with the seal thanks to
gravity keeping the two away from each other, and the caps along with the
PSU remain fully operational. Other PSUs have caps in other orientation
meaning they are bound to fail unless the machine one is in is stored in
an odd orientation, e.g. upside down.
It's best to replace them all anyway at the earliest convenience.
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