On Wed, 2 Nov 2022, Peter Coghlan via cctalk wrote:
Did you have
to replace the power LED at all? I've just bench-tested the PSU
I've swapped the X2 cap in (luckily it powers up without a load, so all I
did was hook up a DVM and check out the voltages), and I noticed that the
LED didn't light. I'm pretty sure I connected it back (and it is keyed!) so
I think I may be looking for a replacement. Something in the back of my mind
says that there is something that makes the replacement slightly non-trivial
(funny LED, odd housing it fits in, some trick to getting it out ... I can't
The LED is more than just a power on indicator. When it fails to light,
it can indicate that something is not right in the PSU. It may tie in
with the "power good" output from the PSU.
It does. I have an H7821 PSU where the LED lights briefly upon power-on
and then goes dark. The PSU cannot be used to power a mainboard as it
does not come up, however it works just fine with storage in an expansion
box. It is one of those that I recapped after leaks have appeared; in
fact it is the one that made me aware of the problem in the first place.
I'll have to get back to it sometime to get this sorted.
It could be that it is failing to light because the
regulation is not
working properly because there is no load. I'd try it with a load
before anything else. The H7822 may need a load on both boards.
There's a 2Ω dummy load on the 5V line in storage expansion boxes powered
by the H7821, so these do require minimum current to work correctly.
BTW was it
just the 1800uF 25V 105degC caps (mine are brown) that you had to
replace? Mine look fine but there are some other large electrolytics in
there (two large brown 470uF voltage unclear, and one large black cap by the
mains input on which I cannot see any of the markings).
It was only the 1800uF 25V capacitors were bad (mine are all brown too).
In an earlier posting I said there were six of them in a H7821 and ten of
them in a H7822. I should have said five in a H7821 and nine in a H7822.
The 470uF 400V capacitors in my units were all fine.
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.
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
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.