Post mortem on an IEC connector

[N_Cook]

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?

 

[N_Cook]

fuses are 5A mains,2AT,5AQ
after cleaning away as much grime as possible , any suggestions for
disguising/absorbing the remanant pong ?

 

[Adrian Tuddenham]

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.

 

[N_Cook]

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.

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.

 

[Adrian Tuddenham]

[...]

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.

 

[N_Cook]

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.

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.

 

[N_Cook]

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.

 

[Eeyore]

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.

Indicates vast overcurrent.

Did someone put aluminium foil in the plugtop fuse ? Typical musician practice.

Graham

 

[Eeyore]

Has someone spilled liquid into it?

If built to BSEN60065 properly it wouldn't matter. Fault currents should be dealt
with by blowing fuses or adequate copper foil thickness / area to withstand the
current.

I'll bet some clot replaced a fuse with some ali foil.

Graham

 

[Eeyore]

Yep, ring crack around a power solder connection, generates lots of
heat.

Possible. A victim of lead-free soldering ?
http://en.wikipedia.org/wiki/Tin_pest

Note that pure tin solder degrades below 13C. Yes that's right. And turns to dust.
Adding a little copper doesn't stop it but slows it some but not enough.

The EU Commission should be strung by their necks from lamp-posts for being a
bunch of technically ignorant twats. Why do they think lead was used in solder in
the first place ? For fun ?

Graham

 

[Eeyore]

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 shit and don't look after
cables and their own personal safety.

Graham

 

[Eeyore]

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

 

[Eeyore]

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

 

[N_Cook]

Just what I've been saying since they first mandated the hateful stuff ...

Arfa

This is a 1998 amplifier, made in China so conventional solder ? does not
look "volcanic" or tin-pesty dusty grey solder points on the boards.

 

[N_Cook]

It probly started off as a hairline crack around one of the soldered
joins, caused by repeated connecting and disconnecting. It started
'fizzling', no one noticed (or cared) until the amp failed to work by
which time there was a socking great hole in the board and a nasty
smell. It`a amazing how long a lot of musicians will put up with faulty
gear, prefering to ignore problems till the item stops working.

Doesn't really need a post mortem.

Ron(UK)

I agree that is the normal etiology and pathology, carrying on the
medico-speak. But this was a socking great burnt patch and billowing smoke
out of the 1/4 inch socket holes, that developed after sound check and
before use proper. Agreed there could have been long term, unnoticed, minor
fizzing but I've never seen this sort of damage in this sort of mains power
line circumstance.

 

[Adrian Tuddenham]

The EU Commission should be strung by their necks from lamp-posts for being a
bunch of technically ignorant twats. Why do they think lead was used in solder
in the first place ? For fun ?

In the past I have many times agreed with your facts, but I have often
disagreed with your way of expressing them. On this occasion I am with
you all the way.

Let's hope the first aeroplane to crash because of lead-free solder has
only Brussels diplomats and anti-lead campaigners on board.

 

[Eeyore]

Do you know the most authorative source/group, academic or industry
expert/s, on tin-pest, lead-free solder, in-service degradation of solder in
connjunction with temperature and vibration. ie those issues, as distinct
from tin whiskers aspect that seems to have more coverage.

ERA, I thin, did a report for the EU which smelt of trying to brush the evidence
under the carpet.

Graham

 

[Eeyore]

To N.Cook The place that I got my research material from was Tin Technology
Ltd with a website of www.lead-free.org The person that I spoke to at that
body, pointed me to www.dti.gov.uk/sustainability/weee/index.htm I also
spoke to a Dr Goodman at ERAT Technology Ltd

That's Paul Goodman at ERA Technology. The final report is here.
http://ec.europa.eu/environment/waste/weee/pdf/era_study_final_report.pdf

There was a simpler 30 or so page interim report I've mislaid which definitely
showed indications of problems from vibration.

Whilst assembly houses may have optimised the processes, for sure it's far more
difficult for an individual to use.

Graham

 

[Eeyore]

That's Paul Goodman at ERA Technology. The final report is here.
http://ec.europa.eu/environment/waste/weee/pdf/era_study_final_report.pdf

There was a simpler 30 or so page interim report I've mislaid which definitely
showed indications of problems from vibration.

Whilst assembly houses may have optimised the processes, for sure it's far more
difficult for an individual to use.

I've emailed Dr Goodman again to see if the simpler report still exists. In the
meantimes this google search gave a host of results.

" ERA interim report lead-free " without the quote marks as I tried it.

Graham

 

[Eeyore]

I`m surprised, it`s a pretty common failure mode.
Bear in mind that the point of arcing usually comes before the
equipments internal mains fuse, but after the fuse in the plug top,
which is more often than not rated at 13amps.
Once the board starts to carbonise quite a large current can flow, and
the current is only flowing between two points it was intented to flow
anyway - at least initially. It doesnt take long for it to burn a hole
in a board.

I'd agree with your analysis. I have seen both hairline cracks such as you
mention and 'cold joints' caused by failure to use an appropriate soldering
temperature, or soldering time when soldering components with large thermal mass
such an IEC connector PCB pin ( pressure will keep it working for a while but
it'll finally go high resistance ). Even seen that on TO-220 devices.

Graham