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

[Alan McKinnon]

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

>
>> 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!

>
> Agreed.



-- 
Alan McKinnon
alan.mckinnon@×××××.com