Post mortem on the body of a resistor
 

Was it 82K or 100K ? Assuming no other info available other than from
the general circuit posistion and other marks of the model , could be
either 82K or 100K.
1/2 watt metal oxide resistor, overheated to totally discolour the bands
and then open circuit.
Scraping an axial line of the laquering off, failure at one end, and the
rest measures 100.9K to the point where the MO is blackened and rapidly
increases in resistance.
Taking readings per turn of the spiral along this axial line, ie
sampling, readings are 1.3K,16.8K,40.5K,63.5K, 94.5k.
Point to consider , as the R failed at an end rather than at the middle,
whether fusible type or manufacturing flaw, it was probably not heated
as much as a resistor that failed in the centre, ie normally the hottest
point as not heatsinked by the tails and solder etc.
I know ,sort of balance of probability-wise , from this data what value
I would select as a replacement. But not wishing to bias anyone else's
opinion, what would others reading this, opt for 82K or 100K ?

Post mortem on the body of a resistor
 

On 4/28/2014 5:14 AM, N_Cook wrote:
Was it 82K or 100K ? Assuming no other info available other than from
the general circuit posistion and other marks of the model , could be
either 82K or 100K.
1/2 watt metal oxide resistor, overheated to totally discolour the bands
and then open circuit.
Scraping an axial line of the laquering off, failure at one end, and the
rest measures 100.9K to the point where the MO is blackened and rapidly
increases in resistance.
Taking readings per turn of the spiral along this axial line, ie
sampling, readings are 1.3K,16.8K,40.5K,63.5K, 94.5k.
Point to consider , as the R failed at an end rather than at the middle,
whether fusible type or manufacturing flaw, it was probably not heated
as much as a resistor that failed in the centre, ie normally the hottest
point as not heatsinked by the tails and solder etc.
I know ,sort of balance of probability-wise , from this data what value
I would select as a replacement. But not wishing to bias anyone else's
opinion, what would others reading this, opt for 82K or 100K ?


Nigel,

If you'd post the make, model and component location you might find
someone here with a schematic and could then know what the original
value is.

Regards,
Tim Schwartz
Bristol Electronics

Post mortem on the body of a resistor
 

On Mon, 28 Apr 2014 10:27:14 -0400 Tim Schwartz wrote
in Message id: :

On 4/28/2014 5:14 AM, N_Cook wrote:
Was it 82K or 100K ? Assuming no other info available other than from
the general circuit posistion and other marks of the model , could be
either 82K or 100K.
1/2 watt metal oxide resistor, overheated to totally discolour the bands
and then open circuit.
Scraping an axial line of the laquering off, failure at one end, and the
rest measures 100.9K to the point where the MO is blackened and rapidly
increases in resistance.
Taking readings per turn of the spiral along this axial line, ie
sampling, readings are 1.3K,16.8K,40.5K,63.5K, 94.5k.
Point to consider , as the R failed at an end rather than at the middle,
whether fusible type or manufacturing flaw, it was probably not heated
as much as a resistor that failed in the centre, ie normally the hottest
point as not heatsinked by the tails and solder etc.
I know ,sort of balance of probability-wise , from this data what value
I would select as a replacement. But not wishing to bias anyone else's
opinion, what would others reading this, opt for 82K or 100K ?


Nigel,

If you'd post the make, model and component location you might find
someone here with a schematic and could then know what the original
value is.

I think he's referring to
Why on earth he started another thread...

Post mortem on the body of a resistor
 

On 28/04/2014 15:27, Tim Schwartz wrote:
On 4/28/2014 5:14 AM, N_Cook wrote:
Was it 82K or 100K ? Assuming no other info available other than from
the general circuit posistion and other marks of the model , could be
either 82K or 100K.
1/2 watt metal oxide resistor, overheated to totally discolour the bands
and then open circuit.
Scraping an axial line of the laquering off, failure at one end, and the
rest measures 100.9K to the point where the MO is blackened and rapidly
increases in resistance.
Taking readings per turn of the spiral along this axial line, ie
sampling, readings are 1.3K,16.8K,40.5K,63.5K, 94.5k.
Point to consider , as the R failed at an end rather than at the middle,
whether fusible type or manufacturing flaw, it was probably not heated
as much as a resistor that failed in the centre, ie normally the hottest
point as not heatsinked by the tails and solder etc.
I know ,sort of balance of probability-wise , from this data what value
I would select as a replacement. But not wishing to bias anyone else's
opinion, what would others reading this, opt for 82K or 100K ?


Nigel,

If you'd post the make, model and component location you might find
someone here with a schematic and could then know what the original
value is.

Regards,
Tim Schwartz
Bristol Electronics




I've since found the schematic forthat Mark and the original value was
probably 91K. I just thought it would be an educative process. I had
previously thought , given the choice of 82K and 100K that it would more
likely to have been 82K from that set of measurements and no other
knowledge. But for the record Fender Concert PR244 of 1994

Post mortem on the body of a resistor
 

R61 of that not so common schematic of the "Concert" family.
http://fmi93superamp.files.wordpress...ice_manual.pdf
Agrees with a number of compared component numbers and values
Next time I have to do that , reminder to myself, keep one DVM-R probe
on the spiral and move the other probe, so alternately down the line, to
get a better set of readings. And also repeat a few times , for an
average. It looks as though, if 4 loops and same end-failure, then take
the reading to use, across the central 2 and double it. The reading
nearest the break obviously had increased the most. The intact end
reading must have been affected by part of the first loop running along
the metal of the end. I would have thought it was the most reliable,
least affected. Also to remember as minimum of scraping with razor
blade, as any thinning of the MO will increase the readings