View Single Post
  #44   Report Post  
Posted to sci.electronics.repair
[email protected] PlainBill47@yawho.com is offline
external usenet poster
 
Posts: 51
Default Power surges and modern electronics.

On Tue, 14 Dec 2010 21:06:23 -0800, Jeff Liebermann
wrote:

On Tue, 14 Dec 2010 17:07:39 -0800 (PST), "larry moe 'n curly"
wrote:

The Pentium4 CPUs in those Dells were such power hogs that even
Rubycons would usually wear out in about 5 years.


Sorta. Caps only dissipate power when current runs through them. In
the case of filter caps, it's the ripple current that causes internal
heating. If you use under-value caps or high ESR caps, you'll have
heating. Among other things, heating causes electrolyte loss. See
the bottom of:
http://www.dfrsolutions.com/uploads/white-papers/Uprating_of_Electrolytic_Capacitors.pdf
for the bad news.

Why has my 1976 Sanyo TV needed only 2 caps replaced (audio coupling,
vertical yoke)? The 2-year-old digital converter box that sits on top
of it has needed a lot more caps replaced.


Because they didn't have decent computers in the 1970's and therefore
could not calculate capacitor values to the bitter edge of near
failure. Designers weren't quite sure what they could get away with,
so they always left a safety factor.

These days, we have CAD workstations and modeling software that will
accurately predict when something will blow. The typical design
criteria is the absolute cheapest components which will fail
immediately after the warranty expires. Similarly, manufacturers of
capacitors didn't have the production controls necessary to accurately
rate their components. So a 6.3WV (working voltage) capacitor was
often really a 10WV capacitor. These days, if it's 6.3V, you fairly
well be certain that it will die a horrible death at a few millivolts
over 6.3V. Your two year old converter box was designed to operate
only up to its probably 1 year warranty. After that, it's actually
desireable for the manufacturer to have it blow up.

There was also an odd preception that electronic devices were suppose
to last "a lifetime". It was not unusual to have TV's and consumer
electronics last 20-30 years without anything more than mechanical
failures. Maybe a dried out electroltyic or blown dial lamps, but not
much more. However, that was bad for business as nobody wanted to
replace something that was still working. Well, that has obviously
changed to the throw-away and eWaste mentality. It sucks, but I have
no clue how to change it. Few seem willing to pay for quality, and
even fewer know quality when they see it.

You missed the basic reason. A 1976 Sanyo TV was an analog TV. The
power supply was largely unregulated. The highest frequency
encountered in the power supply circuits was the 15.625 Khz horizontal
sweep.

The digital converter uses an SMPS power supply, and would have been
considered a very sophisticated computer in 1976.

PlainBill