An amplifier stored exposed to our last UK winter , maybe dropped to -15
degrees C. Loss of the negative side of the biasing area of one channel. By
a secondary route there was some negative V around , did not rise to + rail
or centre and difficult to find
as no reason to suspect a small o/c R. In an area with only -15V secondary
supply and loads of 1N4148 and TO92 around. This resistor was normal 1/3W
4K7, not a fusible resistor, metal oxide spiral construction. On scraping
off the coating , break was 1.5 turns along the 5 turns, ie not central.
Absolutely no sign of heating on original R surface or the board and no sign
of heating with the coating removed. A closely defined break , probing with
DVM. But nothing seen in the way of a crack , bubbling, corrossion or
discolour even under x30 magnification. Could not close the break by
twisting or bending the body of the R.
I've come across mechanically broken R from being dropped but never from
cold or damp.

"N_Cook" wrote in message
...
An amplifier stored exposed to our last UK winter , maybe dropped to -15
degrees C. Loss of the negative side of the biasing area of one channel.
By
a secondary route there was some negative V around , did not rise to +
rail
or centre and difficult to find
as no reason to suspect a small o/c R. In an area with only -15V secondary
supply and loads of 1N4148 and TO92 around. This resistor was normal 1/3W
4K7, not a fusible resistor, metal oxide spiral construction. On scraping
off the coating , break was 1.5 turns along the 5 turns, ie not central.
Absolutely no sign of heating on original R surface or the board and no
sign
of heating with the coating removed. A closely defined break , probing
with
DVM. But nothing seen in the way of a crack , bubbling, corrossion or
discolour even under x30 magnification. Could not close the break by
twisting or bending the body of the R.
I've come across mechanically broken R from being dropped but never from
cold or damp.



Maybe just age or cheap source of parts. In the past year or so I have had a
bad 56 K resistor, a bad 39K resistor, and a bad 18K resistor, all in
amplifiers, none burned or stressed. Two of them were in units about 25
years old; the other about 10 years old. Caused by your cold winter?
Perhaps, perhaps not. Co-incidence doesn't necessarily mean causation.

Mark Z.

Mark Zacharias wrote in message
eb.com...
"N_Cook" wrote in message
...
An amplifier stored exposed to our last UK winter , maybe dropped to -15
degrees C. Loss of the negative side of the biasing area of one channel.
By
a secondary route there was some negative V around , did not rise to +
rail
or centre and difficult to find
as no reason to suspect a small o/c R. In an area with only -15V
secondary
supply and loads of 1N4148 and TO92 around. This resistor was normal
1/3W
4K7, not a fusible resistor, metal oxide spiral construction. On
scraping
off the coating , break was 1.5 turns along the 5 turns, ie not central.
Absolutely no sign of heating on original R surface or the board and no
sign
of heating with the coating removed. A closely defined break , probing
with
DVM. But nothing seen in the way of a crack , bubbling, corrossion or
discolour even under x30 magnification. Could not close the break by
twisting or bending the body of the R.
I've come across mechanically broken R from being dropped but never from
cold or damp.



Maybe just age or cheap source of parts. In the past year or so I have had
a
bad 56 K resistor, a bad 39K resistor, and a bad 18K resistor, all in
amplifiers, none burned or stressed. Two of them were in units about 25
years old; the other about 10 years old. Caused by your cold winter?
Perhaps, perhaps not. Co-incidence doesn't necessarily mean causation.

Mark Z.



I expected to see a manufacturing void in the MO or something like that, so
some thermal stress met the camel's back.

N_Cook wrote:
An amplifier stored exposed to our last UK winter , maybe dropped to -15
degrees C. Loss of the negative side of the biasing area of one channel. By
a secondary route there was some negative V around , did not rise to + rail
or centre and difficult to find
as no reason to suspect a small o/c R. In an area with only -15V secondary
supply and loads of 1N4148 and TO92 around. This resistor was normal 1/3W
4K7, not a fusible resistor, metal oxide spiral construction. On scraping
off the coating , break was 1.5 turns along the 5 turns, ie not central.
Absolutely no sign of heating on original R surface or the board and no sign
of heating with the coating removed. A closely defined break , probing with
DVM. But nothing seen in the way of a crack , bubbling, corrossion or
discolour even under x30 magnification. Could not close the break by
twisting or bending the body of the R.
I've come across mechanically broken R from being dropped but never from
cold or damp.



Microscopic nick on the wire may have contributed to the failure due to
wire shrinkage from cooling.

Still most parts are designed to handle from at least -40C to +80C in
storage. Here is a link for a paper about testing ww resistors from -55
to +225C with only one failu

http://ieeexplore.ieee.org/xpl/freea...rnumber=991174

"Wirewound resistors were also thermal cycled 1000 times over a
temperature range from -55°C to 225°C with only one failure due to a
broken internal connection. "

John :-#)#


--
(Please post followups or tech enquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

John Robertson wrote in message
...
N_Cook wrote:
An amplifier stored exposed to our last UK winter , maybe dropped to -15
degrees C. Loss of the negative side of the biasing area of one channel.
By
a secondary route there was some negative V around , did not rise to +
rail
or centre and difficult to find
as no reason to suspect a small o/c R. In an area with only -15V secondary
supply and loads of 1N4148 and TO92 around. This resistor was normal 1/3W
4K7, not a fusible resistor, metal oxide spiral construction. On scraping
off the coating , break was 1.5 turns along the 5 turns, ie not central.
Absolutely no sign of heating on original R surface or the board and no
sign
of heating with the coating removed. A closely defined break , probing
with
DVM. But nothing seen in the way of a crack , bubbling, corrossion or
discolour even under x30 magnification. Could not close the break by
twisting or bending the body of the R.
I've come across mechanically broken R from being dropped but never from
cold or damp.



Microscopic nick on the wire may have contributed to the failure due to
wire shrinkage from cooling.

Still most parts are designed to handle from at least -40C to +80C in
storage. Here is a link for a paper about testing ww resistors from -55
to +225C with only one failu

http://ieeexplore.ieee.org/xpl/freea...rnumber=991174

"Wirewound resistors were also thermal cycled 1000 times over a
temperature range from -55°C to 225°C with only one failure due to a
broken internal connection. "

John :-#)#


--
(Please post followups or tech enquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."



+++++++

This was metal oxide type. Returning to it I realised I was looking on the
wrong side of the body under the microscope. The failed section was
distributed , puckered and a bit discoloured presumably from
condensation/corrossion and parts flaked off , probably came away with my
breaking off the coating.

N_Cook wrote:
John Robertson wrote in message
...
N_Cook wrote:
An amplifier stored exposed to our last UK winter , maybe dropped to -15
degrees C. Loss of the negative side of the biasing area of one channel.
By
a secondary route there was some negative V around , did not rise to +
rail
or centre and difficult to find
as no reason to suspect a small o/c R. In an area with only -15V secondary
supply and loads of 1N4148 and TO92 around. This resistor was normal 1/3W
4K7, not a fusible resistor, metal oxide spiral construction. On scraping
off the coating , break was 1.5 turns along the 5 turns, ie not central.
Absolutely no sign of heating on original R surface or the board and no
sign
of heating with the coating removed. A closely defined break , probing
with
DVM. But nothing seen in the way of a crack , bubbling, corrossion or
discolour even under x30 magnification. Could not close the break by
twisting or bending the body of the R.
I've come across mechanically broken R from being dropped but never from
cold or damp.



Microscopic nick on the wire may have contributed to the failure due to
wire shrinkage from cooling.

Still most parts are designed to handle from at least -40C to +80C in
storage. Here is a link for a paper about testing ww resistors from -55
to +225C with only one failu

http://ieeexplore.ieee.org/xpl/freea...rnumber=991174

"Wirewound resistors were also thermal cycled 1000 times over a
temperature range from -55°C to 225°C with only one failure due to a
broken internal connection. "

John :-#)#


--


+++++++

This was metal oxide type. Returning to it I realised I was looking on the
wrong side of the body under the microscope. The failed section was
distributed , puckered and a bit discoloured presumably from
condensation/corrossion and parts flaked off , probably came away with my
breaking off the coating.



Ah, right, metal OXIDE (do I need better glasses?)...oh well, at least
you found the culprit!

John ;-#)#
--
(Please post followups or tech enquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."