Re: Motherboard caps

From: Gerard Bok (bok118_at_zonnet.nl)
Date: 02/04/05 

Date: Fri, 04 Feb 2005 13:26:26 GMT

On 3 Feb 2005 08:22:50 -0800, awknod@hotmail.com (purtnoy) wrote:

>Just replaced all the 2700 micr 6.3 volts, with 3300 mic 16 volt caps
>(the 3300 caps are twice as big around,(does that matter?)

Yes. In this case it does matter.
In lineair systems, 'bigger is always better'. On your
motherboard exceeding a capacity value by 50% could disrupt the
entire regulator circuit.
Basic operation in this case is based on energy stored in an
inductor, periodically transferred via a (schottkey)diode into a
low ESR capacitor.

You can only replace those capacitors with types of roughly the
same value, high temperature types and --at least as important--
low ESR values.

> had to
>solder longer legs to raise them up, so they can fit without shorting
>them out.

That also is unacceptable. This will introduce an extra induction
('coil') in series with the capacitor. Take a look at the coils
surrounding those capacitors. And notice that they only have a
few turns, hence very low inductance :-)

The circuit you are working on is likely to be the CPU stepdown
regulator. That is a circuit that transforms 12 volts into
something like 1.55 ... 2.55 volt. At several amperes. 

-- 
Kind regards,
Gerard Bok

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