4 Dec
2007
4 Dec
'07
2:48 p.m.
J Blaser wrote:
Quoting Tony Duell <ard at
p850ug1.demon.co.uk>:
I finally got a little time to take another look at this 5V supply.
I removed all connections to the backplane, etc., then connected my
4-filament rig of headlamps as the only load and powered up. I see the
same results as before, about 0.8V (a bit variable) on the 5V output.
So I guess we can safely say that the problem lies within the PS itself,
and not in anything that it's connected to. I'll add that I hear a
not-loud-but-noticable 'DZZZ' sound from the PS (not just now, it's been
there from the beginning), probably the crowbar doing something. Still,
I think I have a suitable load with the headlamps.
Tony, if your offer still stands, I'd appreciate some advice on how best
to proceed. If you could give me a couple of ideas about what would be
good test points to get started with, I'll give it a go. As I said
earlier, I have a modest set of tools, e.g., VOM and oscilloscope.
I have the 2.5V (H7104-C) and 5V (H7104-D) PSU printsets, found at:
http://vt100.net/mirror/hcps/h7104-c.pdf
http://vt100.net/mirror/hcps/h7104-d.pdf
I admit, I'm not making much sense of them at the moment.
FWIW, I have no experience working inside of switching PSUs, so I have
no knowledge (good or bad) to draw upon.
Many thanks.
- Jared
But I can be eaily persuaded to look at the PSU
schematics sometime and
see if I spot anything obvious. Or at least tlak you through the design
(which might be somewhat unconventional if other DEC supplies are
anything to go by [1])
[1] This might not be a problem for you. If oyu don't have any experience
of SMPSUs, any one is as good/bad as another to get started with. The
problems generally come if you have fixed ideas ofg how supplies should
work and then you get something strange thrown at you.
Thanks much for the offer to work me through this! There are a couple of things
that I want to do tomorrow night when I get a chance.