[sdiy] is this PSU OK?

[Happy Harry]

Not necessarily....

If it is the chopping signal you are seeing... and you ground
the probes you might NOT see the problem... Think of generating
a square wave between the voltage of the upper trace and the lower
trace... if they are the same you cannot see any glitches... but
if they differ you see the chop frequency...

oooh... maybe the scope is actually in ALTERNATE mode and sweeping
two very different signals ???

That's why I suggested using ONE channel to eliminate this possibility.


H^) harry (whose scope does not chop very well following an encounter
of the ungrounded high voltage discharge kind....)


>From: Scott Gravenhorst <music.maker at gte.net>
>Reply-To: music.maker at gte.net
>To: synth-diy at dropmix.xs4all.nl
>Subject: Re: [sdiy] is this PSU OK?
>Date: Fri, 24 Aug 2001 14:09:17
>
>Well, if you ground the probe tip with the scope set the
>way the problem appears, it should still do it if there's
>an issue with the scope.  (AFAIK)
>
>harrybissell at prodigy.net wrote:
> >Do you have a dual trace scope... are both channels ON ???
> >
> >Try using one channel only... The scope may be set to chop mode
> >and it is bouncing from channel to channel...
> >
> >But every 3mS for this chop would normally be WAY too slow. Usually
> >you could only see chopping at very fast sweep speeds.
> >
> >Do you have a 10X sweep switch ??  It might be .5mS you are looking at
> >
> >Notice... I'm suspecting your test equipment here rather than the 
>circuit.
> >You need to convince yourself that this signal is real...
> >
> >Try looking at some other, known signals like the probe cal output
> >of the scope.
> >
> >With the AC coupling you could see ripple and noise... It sounds like 
>your
> >ripple and noise are VERY low, if the measurement is correct.
> >
> >Once you switch to DC, you will probably have to be at maybe 2V to 5V
> >per division to see the "whole" signal.
> >
> >If you set the vertical gain higher, the signal should blow right off the
> >screen.
> >
> >H^)  harry
> >
> >PS : are you SURE you wanna tie the mains ground to the 0VDC point ?
> >I'd do that later (maybe much later)
> >
> >
> >
> >>From: ElmacacoX at aol.com
> >>To: synth-diy at dropmix.xs4all.nl
> >>Subject: [sdiy] is this PSU OK?
> >>Date: Fri, 24 Aug 2001 14:03:43 EDT
> >>
> >>Hi Everybody,
> >>
> >>I am looking at a power supply I made on the scope, and I am not sure if 
>it
> >>is working right.
> >>
> >>I have the settings at 5ms /cm and .01 volts/CM, when AC coupled I get 
>what
> >>looks like noise that ranges about one fifth of one cm, so .0020V, when 
>DC
> >>coupled I get what looks like a straight line that is kind of dotted, 
>every
> >>3ms there is a little gap, and it looks like the trace is shooting 
>upward
> >>vey
> >>quickly at these gaps and they appear to shoot up to the top of the 
>screen.
> >>but when I change the volt/div settings to chase itand see how far it
> >>spikes,
> >>it becomes a solid bar, but it is still present when changing the time
> >>settings.
> >>
> >>
> >>
> >>the power supply is basically like this,
> >>
> >>         ----------------
> >>---------------4700uf--1000uf-100nF--317---10uFelco--100nF
> >>[24VCT at 1.25A]  4x 4001 rect,diodes
> >>        -----------------
> >>----------------4700uf--1000uf-100nF--337--10uF elco-100nF
> >>
> >>
> >>the first three caps are electolytic as is the 10uF at the end.
> >>I am thinking that maybe the 10uf is too big to be at the end like that,
> >>but
> >>the schemo I got it from had them.
> >>I have all the caps and stuff wired correctly the PS works, giving out 
>+/-
> >>12.3V,
> >>although I don't have the mains ground wired to the secondary 0v yet.
> >>
> >>what mai doin wrong?
> >>
> >>thanks
> >>
> >>Ed
> >
> >
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>


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