Re: Help identify mystery piece on 4-meg mem card

[rubywand@aol.com (RUBYWAND)]

In article <Pine.SGI.3.91.951122175415.9986A-100000@umbc7.umbc.edu>,
Robert Rivkin <rrivkin@umbc.edu> writes:

>  At the extreme left of the card between the upper and lower 
>banks 
>of chips there is what appears to be a capacitor--this shows a resistance

>of 1.8 ohms, has its yellow top burned completely off, and appears to 
>have a cylinder of carbon inside--and is labeled C10.  At the extreme 
>right of the card is another part identical in appearance, same 
>resistance, marked C21.  Its appearance is intact.  It also shows a 
>resistance of 1.8 ohms.

    The yellow things sound like small chokes (coils wound on ferrite
cores).  The one that's messy looking seems to have been caught between
the +5V power rail on the board and a short somewhere on the lines
supplying power to chips in two memory banks. Probably, the choke got
pretty hot. There's a decent chance that a bypass capacitor in the 'bad
banks' area has shorted.

    One quickie try at a fix is to examine each of the capacitors in the
messy choke's memory banks. If one 'looks different' (darker, burned,
etc.), remove it and check resistance. If it's shorted, you've found the
culprit.

    If no likely suspects are obvious, you will have to decide whether to
pull caps at random and check each one or remove the IC's and start
looking for the short in a more organized manner. Once the shorted
component is located and replaced, your card should work fine.