2 Nov
2022
2 Nov
'22
5:15 p.m.
Antonio Carlini via cctalk wrote:
On 01/11/2022 23:10, Peter Coghlan via cctalk wrote:
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 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.
To eliminate the LED from enquiries, you could try powering it from a 5V
supply via a 1KOhm resistor or something like that to see if it lights.
If it does, then further investigation in the PSU may be required.
If the LED does turn out to be bad, I forget whether it comes out by
pulling the LED out of the bezel first or taking the ring off the
rear of the bezel first, whichever works.
I've taken the boards out of a whole bunch of
H7821 and H7822 PSUs to
replace the electrolytics without removing the fans. It was difficult at
first but the more I did, the easier it got. I did come across one
seized
fan along the way but I haven't a replacement yet so I haven't got around
to removing the bad one. I should look into it.
I think I have a second H7822 and a pair of H7821 supplies to look at,
so I may well end up getting some practice in!
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 remember unfortunately).
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.
The leaking electrolyte had damaged some other components in some cases,
especially an odd value resistor which seems to have different values in
different units, something around 464 Ohms. It is in series with an
thermistor which seems to control the speed of the fans. I've also had
a zener diode fail which caused problems with the fans. (If the fans
aren't operating properly, the LED might not light!)
Regards,
Peter Coghlan.
Thanks
Antonio
--
Antonio Carlini
antonio(a)acarlini.com