Re: [gentoo-user] Filthy oscilloscope picture! =P

[Fernando Rodriguez]

On Sunday, August 23, 2015 10:34:20 PM Alan McKinnon wrote:
> On 23/08/2015 22:24, Fernando Rodriguez wrote:
> > On Sunday, August 23, 2015 12:14:58 PM Mick wrote:
> >> On Sunday 23 Aug 2015 01:11:03 Fernando Rodriguez wrote:
> >>> On Saturday, August 22, 2015 3:19:50 PM Alan Grimes wrote:
> >>>> Isn't this the filthiest oscilloscope u've seen recently?
> >>>>
> >>>> The only bare metal contact that I could safely use to get a reading off
> >>>> was a +12v line on a spare PCI-E gpu plug. The ground reference is the
> >>>> chassis.
> >>>>
> >>>> You can see the machine's settings in the photo clearly enough. The
> >>>> waveform is fairly constant, it stays in this mode most of the time but
> >>>> sometimes goes into a "low ripple" mode where the ripple falls to +/-
> >>>> 20mv and holds tight. The scaling indicates the upward spikes are
around
> >>>> 0.120 volts and the downward spikes are about 0.22 volts.  This
> >>>> __SHOULD__ be within the input tolerances of the motherboard's
> >>>> regulators.
> >>>
> >>> Regulators don't filter noise, they introduce it. Capacitors do that as
> >>> somebody pointed on the other thread.
> >>>
> >>> So if you're on a tight budget and you have an electronics surplus store
> >>> nearby you can replace all the capacitors on your mobo and PSU (except
the
> >>> big bulky ones on the PSU) for about $3.
> >>
> >> It is quite likely that only the secondary circuit on the PSU needs to
have 
> >> its electrolytic capacitors replaced.  We're talking of anything between
one 
> >> to half a dozen of capacitors.  In all likelihood less than a $1 to $3.
If 
> >> any are even slightly domed I'd start with those and spend no more than a
> > few
> >> cents.
> >>
> >> Primary circuit ceramic capacitors (transient protection) could have been
> >> affected if the PSU was submitted to high surges in the mains supply.  I
had 
> >> one go bad on me after sheet lightning hit the area once.  Its
replacement 
> >> along with a resistor fixed the PSU without any further problems and to
much 
> >> of my surprise - I thought it was a gonner!
> >>
> >> Domed capacitors on the MoBo is a different story.  Quite likely other
> >> components would have been affected and many of them are surface mounted.
> >> You'll need a magnifying glass and steady hands for those.  It is not
> >> something I would attempt in haste, as it is easy to damage more
components 
> >> than what you fix on a MoBo.  YMMV.
> >
> > I don't think it's very likely to have damanged something else if it's
just 
> > noise, but then again I'm not an electronics engineer, this is just a
hobby of 
> > mine so you may be right. Though I can tell you that I have gotten a few
> > damaged boards to work like new by just replacing the electrolitic caps.
>
> That's quite normal - electrolytic caps are the only electronic
> components that can be considered to "wear out". Apart from batteries of
> course :-)
>
> Getting the caps off modern motherboards is a real PITA though - surface
> mount caps need semi-specialized equipment: a proper soldering iron or
> hot air pencil with a very fine tip, desolder braid, a magnifier and a
> very steady hand

For the tiny SMT ones I usually use an worn out iron tip (cause it may get 
plastic on it), heat the whole thing up and push it aside if there's room, 
then pull them off with twizzers and a little bit for force, clean up the 
contacts with braid. If they're many I use solder paste and an oven the get 
new ones on.

But usually there's still a few through hole electrolytics (at least on boards 
old enough to be failing) and those are the ones that fail. When they're SMT 
it's usually a relatively big one or an SMT can and I only seen those fail on 
homemade or dev boards when I do something stupid. For the canned ones I heat 
the can up until it comes off. The real PITA with those is that you usually 
don't find those at a local store.
 
> >
> >> PS. Noisy PSUs are nothing new.  The noise is can be caused by the
> > capacitors,
> >> or the coils.  Although annoying it does not necessarily mean that there
is 
> > an
> >> electrical problem with the components.  If the fan is rattling, then a
drop 
> >> of oil on its bearing should soon put a stop to this.  As Dale mentioned,
a 
> >> stalled fan will not help the longevity of the remaining components.  :-)
>
> I recall an ancient TV from the mid '70s (Blaupunkt) that would
> sometimes develop a rattle in one of the drive circuit coils. Damn thing
> would sound like a hive of bees inside the cabinet!

-- 
Fernando Rodriguez