Post mortem on an IEC connector

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

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.

amp

seems

ok

melting

just

tens

have

track or

could

ohm

before

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

ing

Yep, ring crack around a power solder connection, generates lots of heat. If you can clean away the char, do it (I've used glass bead blasting to good effect). Paint the affected region with Q-dope/styrene varnish/corona dope when cleaning/soldering/flux cleaning is done.

Replace any AC fittings that look damaged, of course.

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.

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.

connection

opinions.

plug, 4

fuses

plug

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IEC-compliant,

with

no

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

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

Indicates vast overcurrent.

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

Graham

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

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 s*it and don't look after cables and their own personal safety.

Graham

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

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

Graham

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

Graham

That's Paul Goodman at ERA Technology. The final report is here.

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

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

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

mass

p.s. ( The TO-220 device acting as a heatsink to the solder via its leads, hence preventing the alloying connection needed ). I've literally seen TO-220 devices 'fall out' of a PCB after a year or two leaving 3 nice rectangular holes in what look to be perfect solder joints.

p.p.s The hairline crack around soldered joints is especially common where the drilled hole size is not ideal ( oversize ) for the lead diameter. I have seen manufacturers specify hole sizes very poorly with the inevitable outcome. Hence my PCB footprints often use my own estimation of the appropriate drill size rather than the data book one. Plenty of other people do the same.

Graham

I did not find , on this site, the expected date for the results of their study

CALCE Long-Term Pb-Free Study

Generally, it seems to be just anecdotal evidence so far

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Hence my

rather than

My Dad - who taught me to solder some 50 years ago - use to say that a good solder joint started off as a good mechanical joint.

As a teeenager, I probably spent thousands of hours wiring up uniselectors and GPO relays with tinned copper wire and sleeving, on every joint, the wire was either wound around the tag or passed through a hole, if it was a lead through a circuit board, the wire was bent over at right angles on the solder side.

We manufacturerd slot machines btw.

Ron