18 Nov
2022
18 Nov
'22
2:51 a.m.
Maciej W. Rozycki via cctalk wrote:
Same here, five 1800uF 25V caps to replace in the H7821 according to my
notes. Overall if you spot a cap that says SXF on it, then replace it
right away whether already leaking or not. These were made by Chemi-con.
Other Chemi-con lines reported problematic are SXE and LXF, though from
own experience they seem less prone.
Also Nichicon PL and PF parts may have to be replaced, I have seen the
former ones actually leaking in other DEC PSUs, such as the H7826, which
is also infested by SXF parts in various capacitances. Both kinds leaked
in a generic industrial Bel Power PSU used with a Cisco device.
I agree that all the 1800uF capacitors should be replaced whether leaking
or not. When I first checked all my H7821 power supplies, I found some
that looked absolutely fine. However, after I started using them for a
while, problems began to show up and when I checked them again, they were
leaking badly.
Sadly the problem with component shortage has hit capacitors as well and
some that used to be readily available are not anymore and prices have
risen too.
Even if replacements are not available, I would suggest immediately removing
any capacitors that are showing any signs of leakage and cleaning the affected
area in order to limit damage from the leakage.
NB I wasn't aware about the problem with RIFA capacitors, it seems like I
might have to replace them in several PSUs I have already recapped, sigh.
I haven't seen any of them fail though, not at least in an obvious way.
I wouldn't worry too much about the RIFAs. Their failure mode is to produce
lots of smoke a short while after switch on. Apart from a bit of soot, they
don't do any damage to anything else while the faulty electrolytics can do a
considerable amount of damage without any visible external sign that anything
is wrong. I haven't seen any failures of any of the RIFAs in my H7821 or
H7822 power supplies and even if they are going to fail eventually, I am
happy enough to wait for this to happen before doing anything about it because
it will be obvious to me when they do fail and the consequences of their
failure are not severe anyway.
Regards,
Peter Coghlan
HTH,
Maciej