4 Sep
2007
4 Sep
'07
7:34 p.m.
On Tuesday 04 September 2007 05:12, J Blaser wrote:
What pops into my head on reading this is that you might possibly be seeing
some sort of an artifact, if you're using a digital meter!
One point about ferroresonant transformers -- that capacitor you mention is
typically "selected" to go with that particular transformer. If you look,
you'll probably find a small dot of the same color paint on both of them.
IIRC, the
'raw DC' is unregulated, just rectified and smoothed from the
transformer. As is the 24V line. Both are about 1.7* what they should be.
That's the strange thing to me. The two secondaries from the transformer
(one for the 24V line, and the other for the 10V line [which sources the
regulated 5V output]) are 'proper' at 27.8V and 11.2V, respectively. What
I don't understand is how a 24V line can suddenly produce 42V! It's like
something is 'pumping' the circuit, and I admit I have never studied how
such things work. The funny thing is that the 5V regulation is working,
even with 17V input
instead of 10V.
A faulty cap can have all sorts of noise, hum, hash, and other nonsense
riding on top of the DC level, and that might (falsely) end up giving you a
higher reading than what you'd expect.
It's gettign late, so I'll not find the
prints tonight. But IIRC, the
transformer in this supply is a ferroresonant one, and that's what
stabilises the 'raw' and 24V lines. What happens if the capacitor hung
off that is defective?
Fair point, but can a faulty capacitor 'pump' up the voltage like I'm
seeing? I suspect the
last part is very ture. Actually replacing the faulty part
is the easy bit :-)
Hey, thanks for your confidence! :-) I can use a little outside support!
;-)
Let me add that this RX01 is the second of two RX01 units in this system.
When I went through the first one a week ago, it checked out fine...that is
I saw 25V/10.2v on the outputs, without a load.
And you're not going to like this :-), but for an electronics novice,
tonight I followed my instinct and swapped the regulator PCBs between
units. Yup, the 'good' system's PCB now is putting out 42V and 17V! So,
it's not the regulation circuit, I guess, or any component on the two
system's PCBs.
But after swapping the PS regulator PCBs, all that's left are the
transformer (which appears to be putting out 'expected' voltages), a 660V
AC capacitor thingy (which I obviously don't understand...is it part of the
ferrroresonance?) that only connects back to the transformer itself, and
the two smoothing caps (one for the 24V line and one for the 10V line). Is
it possible that one/both caps are 'pumping' the circuit? <shrug>
I'm
just too novice to know. Another suggestion I received privately hints that
putting a dummy load
on the PS might bring it into line, and that I will try. I have access to
an oscilloscope, and will put it on the thing, too, to see if I can
discover anything strange.
One more point about ferroresonant transformers -- their output is often NOT
sinewave, but a rather distorted waveform, that would tend to upset some
meters, I'd think. Your scope should show you more of what's actually going
on there.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin