Resistor lied to me

[Matt J. McCullar]

I found an unusual problem on a circuit board yesterday. This board uses
resistors that are not identified by color codes, but instead have a
three-digit code printed on them, much like many capacitors do. These are
not surface-mount devices, just plain, old thru-hole solder types.

I found one resistor labeled "152." That means it's 1.5k ohms. However,
when I took it out of circuit and measured it, it was actually 15k! (There
were plenty of other "152" resistors on this board for comparison, so that's
how we know for sure it was bad.) Replacing this resistor cured the board
problem, but it struck me as very unusual that a resistor would happen to
increase its resistance by an exact order of magnitude.

This does not appear to be a manufacturing defect, as zapping it with a heat
gun later on made the value wander all over the place. It just happened to
settle on that particular value at that particular time. A casual glance by
a technician in a hurry may not have caught it (i.e. Me, when working on the
board previously.)

Matt J. McCullar, KJ5BA
Arlington, TX

 

[David Sewell]

Been there...
Sods law These things are sent to try us. Don't you just hate it when
that happens.

David

 

[Mark D. Zacharias]

A dealer once gave me a Hafler bridge mod to do when they couln't get it to
work. I couldn't either, until I discovered one of the resistors on the mod
board was color-coded wrong. It read a standard value, just didn't
correspond to the color-code printed on it.

Mark Z.



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"David Sewell" <david@hereat.freeserve.co.uk> wrote in message
news:buc06a$jev$1@newsg1.svr.pol.co.uk...

Been there...
Sods law These things are sent to try us. Don't you just hate it
when
that happens.

David