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.


More information about the cctalk mailing list