Adrian Tuddenham wrote in message
valid.invalid...
N_Cook wrote:

Obviously I've come acros melting/burning, starting from bad connection
arcing , but not this amount of damage, so am requesting other opinions.

A superfluity of mains fuses all ok, on 240V UK mains, 5 amp in plug, 4
amp
chassis mounted and internal 5 amp all in series. Mains transformer
seems
right sort of primary and secondary resistance. All other internal fuses
ok
and no other visually obvious problems.
Burning right thru the pcb for 1/2 inch around the L pin of the IEC,
melting
of the plastic of the IEC above the burning and even the linecord plug
surrounding the L pin melting where heat conducted through the pin
presumably. Remainder of IEC receptacle distorted from heat but holding
together.
The N pin soldering at the pcb is bad, but has continuity, I assume
pre-existing rather than from heat damage as 3/4 inch from the main L
arcing, so temp would not have reached solder melt point on the N pin. I
assume the L pin solder was worse and initial cause of arcing. Amp was
just
idling , with no sound throughput, is that why so much damage as only
tens
of mA passing in the arcs. ? If 0.5 amp or more, then the damage would
have
been more extreme , but shorter duration, before total break in pcb
track or
solder joint meant a fuse action in effect, before greater heat damage
could
take effect. The remnant pcb charring is not obviously conductive (30 M
ohm
DVM)

Incidently the earth pin soldering although smoke stained looks fine,
coincidence? or passing of electricity have an initiation effect on good
solder to become bad or does it require porous solder or something
inherently bad with it for a heating effect to come into play, long
before
any full arcing?

Has someone spilled liquid into it?

If you measured the resistance of the charring with low voltage, you
might have had a false high reading; with 240v you could find that it
flashes over or sputters badly.

What would the normal running current and the maximum fault current from
a shorted transformer secondary have been? A bad joint of 5k-ohms in a
circuit carrying 20 mA will develop 2 watts, which is enough to char a
PCB.


I have come across some connector pairs purporting to be IEC-compliant,
where the pins and the socket connections hardly touched. I submitted
them to Trading Standards and was told that both halves did comply with
the specification - so you might have come across a similar problem to
that; and the fault may not be in the soldering.



--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk



Where the pins of the IEC chassis part go through the plastic there is no
melting or burning but the linecord plug (softer plastic) shows signs of
melting around the line pin , no burning. So the initial problem not
mis-mating of IEC pins. Downstream problems , transformer, ps etc is
possible I suppose , no blown fuses though.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

N_Cook wrote:

Adrian Tuddenham wrote in message
valid.invalid...
N_Cook wrote:

Obviously I've come acros melting/burning, starting from bad connection
arcing , but not this amount of damage, so am requesting other opinions.

A superfluity of mains fuses all ok, on 240V UK mains, 5 amp in plug, 4
amp
chassis mounted and internal 5 amp all in series. Mains transformer
seems
right sort of primary and secondary resistance. All other internal fuses
ok
and no other visually obvious problems.
Burning right thru the pcb for 1/2 inch around the L pin of the IEC,
melting
of the plastic of the IEC above the burning and even the linecord plug
surrounding the L pin melting where heat conducted through the pin
presumably. Remainder of IEC receptacle distorted from heat but holding
together.
[...]

I have come across some connector pairs purporting to be IEC-compliant,
where the pins and the socket connections hardly touched. I submitted
them to Trading Standards and was told that both halves did comply with
the specification - so you might have come across a similar problem to
that; and the fault may not be in the soldering.



Where the pins of the IEC chassis part go through the plastic there is no
melting or burning but the linecord plug (softer plastic) shows signs of
melting around the line pin , no burning.

Some of those IEC chassis connectors are almost indestructible. I have
tried to melt one of the pins out of one with a soldering iron and it
simply would not move. I had to tear the rivetted tag off the back with
a vice, then file down the remains of the pin and punch it out.

I can quite believe that the items each side could be damaged by heat
but the connector in the middle would show no signs of burning.

So the initial problem not
mis-mating of IEC pins. Downstream problems , transformer, ps etc is
possible I suppose , no blown fuses though.

If the direct cause of the heat was a high resistance joint, you
wouldn't expect a blown fuse. A shorted secondary on a small
transformer wouldn't necessarily blow the fuse either.

It has occurred to me that if a solder joint had gone high resistance,
the increase in temperature would either melt it back together or blow
it open before the board became damaged. I still think a poor
plug/socket connection is a likely cause.


--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

Adrian Tuddenham wrote in message
valid.invalid...
N_Cook wrote:

Adrian Tuddenham wrote in message
valid.invalid...
N_Cook wrote:

Obviously I've come acros melting/burning, starting from bad
connection
arcing , but not this amount of damage, so am requesting other
opinions.

A superfluity of mains fuses all ok, on 240V UK mains, 5 amp in
plug, 4
amp
chassis mounted and internal 5 amp all in series. Mains transformer
seems
right sort of primary and secondary resistance. All other internal
fuses
ok
and no other visually obvious problems.
Burning right thru the pcb for 1/2 inch around the L pin of the IEC,
melting
of the plastic of the IEC above the burning and even the linecord
plug
surrounding the L pin melting where heat conducted through the pin
presumably. Remainder of IEC receptacle distorted from heat but
holding
together.
[...]

I have come across some connector pairs purporting to be
IEC-compliant,
where the pins and the socket connections hardly touched. I submitted
them to Trading Standards and was told that both halves did comply
with
the specification - so you might have come across a similar problem to
that; and the fault may not be in the soldering.



Where the pins of the IEC chassis part go through the plastic there is
no
melting or burning but the linecord plug (softer plastic) shows signs of
melting around the line pin , no burning.

Some of those IEC chassis connectors are almost indestructible. I have
tried to melt one of the pins out of one with a soldering iron and it
simply would not move. I had to tear the rivetted tag off the back with
a vice, then file down the remains of the pin and punch it out.

I can quite believe that the items each side could be damaged by heat
but the connector in the middle would show no signs of burning.

So the initial problem not
mis-mating of IEC pins. Downstream problems , transformer, ps etc is
possible I suppose , no blown fuses though.

If the direct cause of the heat was a high resistance joint, you
wouldn't expect a blown fuse. A shorted secondary on a small
transformer wouldn't necessarily blow the fuse either.

It has occurred to me that if a solder joint had gone high resistance,
the increase in temperature would either melt it back together or blow
it open before the board became damaged. I still think a poor
plug/socket connection is a likely cause.


--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

The half inch radius destruction was total , burning down to glass mat , the
thickness of the board. I just cannot see that happening due to an arcing
contact inside the mated plug and socket and the heat conducted through an
inch or so of metal conductor , with only marginal melting to the line cord
plug.

Without carving into the line plug I cannot see the surface of the female
part but the male pins in the chassis section show no pitting or sign of
arcing.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

N_Cook wrote:

Without carving into the line plug I cannot see the surface of the female
part but the male pins in the chassis section show no pitting or sign of
arcing.

If you're reading my posts ( which I doubt since you ask so many daft questions
the answers to which that you ought to *know ) do these thing.

Insert the apparently undamaged part into a new mating half. Does it hold firm ?

Apply a serious current through each contact and measure the volt drop. That'll
tell you the contact resistance from which much can be deduced.

And when bands bring in gear with 'tatty' mains leads, replace them and destroy
the defective one ( hand it back in a bag). They cost bugger all and could save
a life.

Also check the plugtop fuse rating fitted. It's easy to put a 13A fuse in the
plug of a 5A lead. And VERY stupid.

Graham

Adrian Tuddenham wrote:

I still think a poor plug/socket connection is a likely cause.

Loose contact pressure high resistance joint. I've heard of it and had it
reported to me but never seen it personally.

It happens when cheapskate bands treat their kit like **** and don't look after
cables and their own personal safety.

Graham

Another maybe relevant factor. The IEC socket was rivetted to the pcb and
very firm but the section that is chassis mounted had much smaller diameter
screws than I would normally expect. Although star washers under the nuts
they undid easily. Maybe that due to the heating but also could be due to
normal inserting of cord into socket straining the pcb solder connections
over years of use/stowage. Would also explain why no obvious bad solder on
the ground pin as that is mechanically more remote by another half inch of
conductor compared to the active conductor lengths.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

N_Cook wrote:

Another maybe relevant factor. The IEC socket was rivetted to the pcb and
very firm but the section that is chassis mounted had much smaller diameter
screws than I would normally expect. Although star washers under the nuts
they undid easily. Maybe that due to the heating but also could be due to
normal inserting of cord into socket straining the pcb solder connections
over years of use/stowage. Would also explain why no obvious bad solder on
the ground pin as that is mechanically more remote by another half inch of
conductor compared to the active conductor lengths.

Look for the basics instead of pontificating. That's where it'll be. Getting on
for 40 yrs experience tells me that.

Graham