[sdiy] is this PSU OK?

[Scott Gravenhorst]

Yes, but if it still happens with the probe tip
grounded, then it *cannot* be the PSU.

harrybissell at prodigy.net wrote:
>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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>>- The media's credibility should always be questioned.
>>
>>-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
>>-- Linux Rex         | RedWebMail by RedStarWare
>>-- FatMan: www.teklab.com/~chordman
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>>
>>
>
>
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=========================================================  
- Government: The other religion.
- The media's credibility should always be questioned.

-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
-- Linux Rex         | RedWebMail by RedStarWare
-- FatMan: www.teklab.com/~chordman
-- NonFatMan: members.xoom.com/_XMCM/chordman/index.html