14 Sep
2014
14 Sep
'14
10:46 a.m.
First, thanks to everyone for the help; this is really a puzzler for me, and I
really appreciate the assistance. Anyway, on to substance (several replies all
packaged into one to minimize list traffic - and sorry the result is a bit of
a tome):
From: Tothwolf
What caused the excessive current draw though? Is
there a marginal part
on the pc board? You shouldn't be seeing that much current draw though
a pc board.
I realized after I posted is that your first question is the $64K question -
and I don't know the answer. I suppose it could (broadly) be one of four
things:
- The previous owner tried to draw too much power (although the boards
that were plugged in when I bought it shouldn't have done that - I haven't
sat down to calculate the total draw, and compare it with what the PS can
supply, but the card cage was less than half full of stock items)
- There's a fault (e.g. partial short), or faulty component, somewhere
in the power supply
- The connector is under-specified for the current it could be/was asked
to carry
- There's a poor connection somewhere in the connector system, further
dividable into:
-- The wire<->terminal joint
-- The terminal<->lug joint
-- The lug<->PCB joint
I agree that without knowing the original cause, and correcting it, the
problem could recur - but I don't think I can (at this remove) work out which
one it was. So I can take some corrective action(s), but I don't think I can
be sure I got the orignal cause...
The first question that comes to mind for me, is the
terminal even
original to the chassis or did someone replace it at some point in the
field?
Well, I'd have said 'original' (it has the look/feel of original work), but
looking closely, I cannot be sure. It's the only connector of that type in the
PS - the other +5V lines are i) soldered to the tips of the rectifiers in the
full-wave bridge, and ii) use crimped bolt-on type terminals (i.e. not the
push-on tabs) for the rest. Those latter do have the same colour and general
look as this one, _but_ the crimping marks on their insulators are more
distinct. (Perhaps the heat removed them on this one?)
If it was a poor wire<->terminal connection, could that really have melted
the solder on the lug<->PCB joint?
Is that terminal a dual crimped type with a separate
insulation crimp?
Sorry, how would I tell?
The .250 tab type terminal on the board is likely made
by either AMP or
Molex and would probably be pretty easy to source as a replacement part.
I read this to mean you think I should replace the soldered on tab (presumably
as well as the crimped terminal on the wire)?
Done correctly, using the right compression dies and
tools, crimped
connections are always far more secure and reliable both mechanically
and electrically
Alas, while I have a fairly well-equipped shop, it doesn't run to the
right compression dies and tools...
From: Chuck Guzis
You may want to consider a standard PCB screw lug
Well, I'd have to modify the PCB, which I'm loathe to do. The current tab uses
two round pins to make the connection to the PCB, which I suppose I could cut
into a slot, but there are other components in the immediate vicinity (seems
odd for such a high-current connection, but...)
From: Paul Koning
Solder helps keep things mechanically sound, but for
high current
connections a well executed crimp is probably better.
Really? I thought that while AC was carried in the skin of a conductor, DC was
carried spread evenly throughout, so I assume(d) that the wider cross-section
of a soldered connection would allow it to carry more current.
Perhaps the industries that stopped using soldered connections in favour of
crimped did so because with hand-soldering, you can get variation (and also
of course bad solder joints), whereas with a crimp it's pretty uniform from
joint to joint?
What I would do is pull the old lug off, clean off the
wire, and crimp
on a new lug
Ah, to make sure I understand, you're talking about replacing the terminal
attached to the wire, right? (I tend to think of the 'lug' as the
spade-shaped thing soldered onto the board.)
with a good quality (commercial grade, not Radio
Shack) ratchet crimp
tool.
And if I don't have such a tool... ?
If it's done right it should be on very tight; if
you can pull it off
without serious force it's either the wrong size lug or the wrong tool.
You're talking about the wire into the terminal here, right? Yes, I've
always made sure a crimped wire _cannot_ be pulled loose (whatever size
connector).
FWIW, the terminal onto the lug is a pretty tight fit, too - I can wiggle it
with my fingers, but to get it off I'm going to need some mechanical help.
Noel
14 Sep
14 Sep
2:59 p.m.
This is very interesting... I had participated in a similar discussion on
what is more a tradesperson's board some months ago; it's fun to get the
perspective of some engineers and computer guys here.
I personally was trained that soldering is typically the superior method SO
LONG AS YOU ARE DOING IT CORRECTLY.
Unfortunately, most folks aren't as good at soldering as they think ... :|
I think the consensus on the trades board (mechanics, electricians, etc)
was that while you could achieve good, long-lasting results with both
techniques, given the proper tool, the crimp was more fool-proof, easy to
teach and will give the most consistent results... I can see that, sure,
it's much easier to just tell a technician, strip the wire this far, stick
it in this lug, work the crimper through it's entire range of motion...
easier than, you know, heat the surface not the solder, make sure it's not
beading up, this is how you recognize a good solder joint and don't forget
to put some heat shrink up the wire before you splice em together!
I switch off as the situation dictates... I have a nice Hakko iron as well
as a Crimpmaster with like 15 different die sets (I found someone selling
like every single one, and I stocked up! anyone got a line on MMJ plugs??)
and generally if I don't expect to ever want to change the connection, or
if I am splicing or attaching very small wire (~26 ga) where there isn't
really an appropriate lug size (and I don't want Scotchloks everywhere) I
will solder; I will crimp lugs if I'm doing something more temporary, or if
I deliberately need to attach to something that takes lugs e.g. a terminal
strip, etc.
The [Ideal] Crimpmaster is a nice tool and not too expensive... maybe $40
for the handle and $15-25 for each specific die set you want. You don't
have to go and shell out $400 for the AMP crimper or the Deutsch crimper or
whatever... There are many knock-offs of the Crimpmaster that take the same
dies... probably even cheaper if you need the price point to be lower yet.
Nothing wrong with doubling up the techniques; crimp then solder... I've
done this more than once... when I wanted to REALLY make sure it wasn't
gonna come apart.
In this particular scenario where you are trying to assumedly connect a
wiring harness to a terminal strip on a power supply (?) I'd probably just
crimp it.
All this talk about the skin effect and where AC vs DC travels on the
conductor is tickling my memory but it's been so long... I'm not even gonna
lie, I'd have to refer back to my e-mag textbook on that one, LOL. But,
Noel, I think you are correct?
Best,
Sean
On Sun, Sep 14, 2014 at 6:46 AM, Noel Chiappa <jnc at mercury.lcs.mit.edu>
wrote:
First, thanks to everyone for the help; this is really
a puzzler for me,
and I
really appreciate the assistance. Anyway, on to substance (several replies
all
packaged into one to minimize list traffic - and sorry the result is a bit
of
a tome):
From: Tothwolf
What caused the excessive current draw though? Is
there a marginal
part
on the pc board? You shouldn't be seeing that
much current draw
though
a pc board.
I realized after I posted is that your first question is the $64K question
-
and I don't know the answer. I suppose it could (broadly) be one of four
things:
- The previous owner tried to draw too much power (although the boards
that were plugged in when I bought it shouldn't have done that - I
haven't
sat down to calculate the total draw, and compare it with what the PS can
supply, but the card cage was less than half full of stock items)
- There's a fault (e.g. partial short), or faulty component, somewhere
in the power supply
- The connector is under-specified for the current it could be/was asked
to carry
- There's a poor connection somewhere in the connector system, further
dividable into:
-- The wire<->terminal joint
-- The terminal<->lug joint
-- The lug<->PCB joint
I agree that without knowing the original cause, and correcting it, the
problem could recur - but I don't think I can (at this remove) work out
which
one it was. So I can take some corrective action(s), but I don't think I
can
be sure I got the orignal cause...
The first question that comes to mind for me, is
the terminal even
original to the chassis or did someone replace it at some point in
the
field?
Well, I'd have said 'original' (it has the look/feel of original work), but
looking closely, I cannot be sure. It's the only connector of that type in
the
PS - the other +5V lines are i) soldered to the tips of the rectifiers in
the
full-wave bridge, and ii) use crimped bolt-on type terminals (i.e. not the
push-on tabs) for the rest. Those latter do have the same colour and
general
look as this one, _but_ the crimping marks on their insulators are more
distinct. (Perhaps the heat removed them on this one?)
If it was a poor wire<->terminal connection, could that really have melted
the solder on the lug<->PCB joint?
Is that terminal a dual crimped type with a
separate insulation
crimp?
Sorry, how would I tell?
The .250 tab type terminal on the board is likely
made by either AMP
or
Molex and would probably be pretty easy to source
as a replacement
part.
I read this to mean you think I should replace the soldered on tab
(presumably
as well as the crimped terminal on the wire)?
Done correctly, using the right compression dies
and tools, crimped
connections are always far more secure and reliable both mechanically
and electrically
Alas, while I have a fairly well-equipped shop, it doesn't run to the
right compression dies and tools...
From: Chuck Guzis
You may want to consider a standard PCB screw lug
Well, I'd have to modify the PCB, which I'm loathe to do. The current tab
uses
two round pins to make the connection to the PCB, which I suppose I could
cut
into a slot, but there are other components in the immediate vicinity
(seems
odd for such a high-current connection, but...)
From: Paul Koning
Solder helps keep things mechanically sound, but
for high current
connections a well executed crimp is probably better.
Really? I thought that while AC was carried in the skin of a conductor, DC
was
carried spread evenly throughout, so I assume(d) that the wider
cross-section
of a soldered connection would allow it to carry more current.
Perhaps the industries that stopped using soldered connections in favour of
crimped did so because with hand-soldering, you can get variation (and also
of course bad solder joints), whereas with a crimp it's pretty uniform from
joint to joint?
What I would do is pull the old lug off, clean
off the wire, and
crimp
on a new lug
Ah, to make sure I understand, you're talking about replacing the terminal
attached to the wire, right? (I tend to think of the 'lug' as the
spade-shaped thing soldered onto the board.)
with a good quality (commercial grade, not Radio
Shack) ratchet crimp
tool.
And if I don't have such a tool... ?
If it's done right it should be on very
tight; if you can pull it off
without serious force it's either the wrong size lug or the wrong
tool.
You're talking about the wire into the terminal here, right? Yes, I've
always made sure a crimped wire _cannot_ be pulled loose (whatever size
connector).
FWIW, the terminal onto the lug is a pretty tight fit, too - I can wiggle
it
with my fingers, but to get it off I'm going to need some mechanical help.
Noel
5:06 p.m.
OK, sorry, I got all excited about talking about soldering vs crimping and
wandered a little bit OT...
So you've got a spade lug terminating a line from a power supply, onto what
I assume is a Q-bus backplane.
The spade lug is just slotting right on top of a big tab soldered into the
board, which in turn probably has a huge trace leading off of it to all the
slots.
Honestly it looks in pretty good shape to me; maybe it just gets a little
hot in there if the backplane is filled to 100% capacity and you are seeing
some discoloration on the insulating outer plastic on the spade lug. Could
just have been "moderate" heat in there and just the grade of the plastic,
you get discoloration over ~30+ years of running it, etc...
I don't see any corrosion in there, or major discoloration on the PCB which
would indicate very high heat at that point; it looks a bit gungy but I
think it's probably just old flux residue and such left over from the
original manufacturing process (or so the pic leads me to believe).
If it really bugs you and you have sufficient slack in the wire to work
with, I would suggest just dyking off the old lug, stripping some clean
wire and then crimping on a new lug. Clean off the solder tab while you're
at it with light wire brush and some contact cleaner.
This sort of spade lug is very common in the electrical trades, you can get
the lugs and tools to crimp them with at your local Home Depot or Lowe's.
As I mentioned in my previous post, a ratcheting crimper with the proper
die is the nicest way to go and not even terribly expensive, but you can
just as well get good serviceable crimps with e.g. a Klein #1005 plain-jane
insulated/noninsulated crimp/cut tool or Klein #1000 multipurpose
electrician tool. Honestly crimping lugs is so trivial I usually just use
my Klein #1000 instead of having to go and swap out the RJ-45 die in my
Crimpmaster (unless I'm dealing with some kind of single digit AWG gorilla
wire...).
(N.B. What you are seeing in your chassis is an insulated spade lug; the
un-insulated lug is basically identical except they lack the outer
insulation. I guess the uninsulated version exists so you can save a penny
in an application where the insulated lug really isn't required. Crimping
either type is the same single-step process; on an insulated connector, you
just crimp right through the whole thing. You can basically turn an
un-insulated lug into a (nominally) insulated lug by applying heat shrink
after crimping)
The lugs are sold to fit various ranges of AWG so...... ultimately you are
limited by whatever wire you are trying to crimp. If you are really
concerned about more power being drawn through whatever rail that is, than
it is really rated for, you should really be focused on the supply wire and
not the lug! (or maybe whatever it is, that is causing excessive current
draw)
But that sort of wire... looks like maybe 14 AWG? +/- 2 without actually
being able to look at the jacket... seems very appropriate for that sort of
application. Not uncommon at all. You have to think, (solid) 14 AWG is good
for like 15A @ 120VAC... that's a lot of power. As well, consider how many
slots it has and how many you intend to fill. If you're only running 30,
40, 50% of the slot compliment, you're well within the rated design of the
cabinet and power supply, you'd think.
Is it not running? If that is the worst you can find in the PSU, I'd bet it
would run fine if you fired it up.
Best,
Sean
On Sun, Sep 14, 2014 at 10:59 AM, Sean Caron <scaron at umich.edu> wrote:
This is very interesting... I had participated in a
similar discussion on
what is more a tradesperson's board some months ago; it's fun to get the
perspective of some engineers and computer guys here.
I personally was trained that soldering is typically the superior method
SO LONG AS YOU ARE DOING IT CORRECTLY.
Unfortunately, most folks aren't as good at soldering as they think ... :|
I think the consensus on the trades board (mechanics, electricians, etc)
was that while you could achieve good, long-lasting results with both
techniques, given the proper tool, the crimp was more fool-proof, easy to
teach and will give the most consistent results... I can see that, sure,
it's much easier to just tell a technician, strip the wire this far, stick
it in this lug, work the crimper through it's entire range of motion...
easier than, you know, heat the surface not the solder, make sure it's not
beading up, this is how you recognize a good solder joint and don't forget
to put some heat shrink up the wire before you splice em together!
I switch off as the situation dictates... I have a nice Hakko iron as well
as a Crimpmaster with like 15 different die sets (I found someone selling
like every single one, and I stocked up! anyone got a line on MMJ plugs??)
and generally if I don't expect to ever want to change the connection, or
if I am splicing or attaching very small wire (~26 ga) where there isn't
really an appropriate lug size (and I don't want Scotchloks everywhere) I
will solder; I will crimp lugs if I'm doing something more temporary, or if
I deliberately need to attach to something that takes lugs e.g. a terminal
strip, etc.
The [Ideal] Crimpmaster is a nice tool and not too expensive... maybe $40
for the handle and $15-25 for each specific die set you want. You don't
have to go and shell out $400 for the AMP crimper or the Deutsch crimper or
whatever... There are many knock-offs of the Crimpmaster that take the same
dies... probably even cheaper if you need the price point to be lower yet.
Nothing wrong with doubling up the techniques; crimp then solder... I've
done this more than once... when I wanted to REALLY make sure it wasn't
gonna come apart.
In this particular scenario where you are trying to assumedly connect a
wiring harness to a terminal strip on a power supply (?) I'd probably just
crimp it.
All this talk about the skin effect and where AC vs DC travels on the
conductor is tickling my memory but it's been so long... I'm not even gonna
lie, I'd have to refer back to my e-mag textbook on that one, LOL. But,
Noel, I think you are correct?
Best,
Sean
On Sun, Sep 14, 2014 at 6:46 AM, Noel Chiappa <jnc at mercury.lcs.mit.edu>
wrote:
First, thanks to everyone for the help; this is
really a puzzler for me,
and I
really appreciate the assistance. Anyway, on to substance (several
replies all
packaged into one to minimize list traffic - and sorry the result is a
bit of
a tome):
From: Tothwolf
What caused the excessive current draw though? Is
there a marginal
part
on the pc board? You shouldn't be seeing that
much current draw
though
a pc board.
I realized after I posted is that your first question is the $64K
question -
and I don't know the answer. I suppose it could (broadly) be one of four
things:
- The previous owner tried to draw too much power (although the boards
that were plugged in when I bought it shouldn't have done that - I
haven't
sat down to calculate the total draw, and compare it with what the PS
can
supply, but the card cage was less than half full of stock items)
- There's a fault (e.g. partial short), or faulty component, somewhere
in the power supply
- The connector is under-specified for the current it could be/was asked
to carry
- There's a poor connection somewhere in the connector system, further
dividable into:
-- The wire<->terminal joint
-- The terminal<->lug joint
-- The lug<->PCB joint
I agree that without knowing the original cause, and correcting it, the
problem could recur - but I don't think I can (at this remove) work out
which
one it was. So I can take some corrective action(s), but I don't think I
can
be sure I got the orignal cause...
The first question that comes to mind for me, is
the terminal even
original to the chassis or did someone replace it at some point in
the
field?
Well, I'd have said 'original' (it has the look/feel of original work),
but
looking closely, I cannot be sure. It's the only connector of that type
in the
PS - the other +5V lines are i) soldered to the tips of the rectifiers in
the
full-wave bridge, and ii) use crimped bolt-on type terminals (i.e. not the
push-on tabs) for the rest. Those latter do have the same colour and
general
look as this one, _but_ the crimping marks on their insulators are more
distinct. (Perhaps the heat removed them on this one?)
If it was a poor wire<->terminal connection, could that really have melted
the solder on the lug<->PCB joint?
Is that terminal a dual crimped type with a
separate insulation
crimp?
Sorry, how would I tell?
The .250 tab type terminal on the board is likely
made by either
AMP or
Molex and would probably be pretty easy to source
as a replacement
part.
I read this to mean you think I should replace the soldered on tab
(presumably
as well as the crimped terminal on the wire)?
Done correctly, using the right compression dies
and tools, crimped
connections are always far more secure and reliable both
mechanically
and electrically
Alas, while I have a fairly well-equipped shop, it doesn't run to the
right compression dies and tools...
From: Chuck Guzis
You may want to consider a standard PCB screw lug
Well, I'd have to modify the PCB, which I'm loathe to do. The current tab
uses
two round pins to make the connection to the PCB, which I suppose I could
cut
into a slot, but there are other components in the immediate vicinity
(seems
odd for such a high-current connection, but...)
From: Paul Koning
Solder helps keep things mechanically sound, but
for high current
connections a well executed crimp is probably better.
Really? I thought that while AC was carried in the skin of a conductor,
DC was
carried spread evenly throughout, so I assume(d) that the wider
cross-section
of a soldered connection would allow it to carry more current.
Perhaps the industries that stopped using soldered connections in favour
of
crimped did so because with hand-soldering, you can get variation (and
also
of course bad solder joints), whereas with a crimp it's pretty uniform
from
joint to joint?
What I would do is pull the old lug off, clean
off the wire, and
crimp
on a new lug
Ah, to make sure I understand, you're talking about replacing the terminal
attached to the wire, right? (I tend to think of the 'lug' as the
spade-shaped thing soldered onto the board.)
with a good quality (commercial grade, not Radio
Shack) ratchet
crimp
tool.
And if I don't have such a tool... ?
If it's done right it should be on very
tight; if you can pull it
off
without serious force it's either the wrong
size lug or the wrong
tool.
You're talking about the wire into the terminal here, right? Yes, I've
always made sure a crimped wire _cannot_ be pulled loose (whatever size
connector).
FWIW, the terminal onto the lug is a pretty tight fit, too - I can wiggle
it
with my fingers, but to get it off I'm going to need some mechanical help.
Noel
15 Sep
15 Sep
11:22 a.m.
On Sun, 14 Sep 2014, Sean Caron wrote:
I switch off as the situation dictates... I have a
nice Hakko iron as
well as a Crimpmaster with like 15 different die sets (I found someone
selling like every single one, and I stocked up! anyone got a line on
MMJ plugs??) and generally if I don't expect to ever want to change the
connection, or if I am splicing or attaching very small wire (~26 ga)
where there isn't really an appropriate lug size (and I don't want
Scotchloks everywhere) I will solder; I will crimp lugs if I'm doing
something more temporary, or if I deliberately need to attach to
something that takes lugs e.g. a terminal strip, etc.
MMJ plugs...yes, I bought up a stash of the Tyco/AMP variety when Tyco
announced they were ceasing production (despite my complaints to Tyco's
management, who claimed this was part of "LEAN production"...what a bunch
of BS). Does your crimper die require the AMP or WE/SS (Western
Electric/Stewart Stamping) variety? Much of my tooling for these is for
the AMP variety, hence why I stocked up. Bel-Stewart (Stewart Connector
Systems) is still manufacturing the WE/SS variety though, so if those are
what you need (most likely), they shouldn't be too difficult to obtain.
http://belfuse.com/ethernet/modular-plugs/
Look under 'keying' for OST, but make sure you get the correct orientation
since they make types with the tab offset on opposite sides. Lego
Mindstorms for example uses OST modular plugs keyed opposite those used
for DEC MMJ.
The [Ideal] Crimpmaster is a nice tool and not too
expensive... maybe
$40 for the handle and $15-25 for each specific die set you want. You
don't have to go and shell out $400 for the AMP crimper or the Deutsch
crimper or whatever... There are many knock-offs of the Crimpmaster that
take the same dies... probably even cheaper if you need the price point
to be lower yet.
If you ever have the chance to grab a secondhand Paladin Tools 8000 series
frame, grab one. It has a lower breakover force and will fit the full
sized Crimpmaster dies. While I have a bunch of these for general purpose
stuff, I still use OEM tooling from AMP/Molex/T&B/etc for most projects.
Interchangeable dies are not available for many discrete contact types too
(AMP CPC or 2mm pitch Hirose or JAE for example).
14 Sep
14 Sep
9:41 p.m.
On Sep 14, 2014, at 6:46 AM, Noel Chiappa <jnc at mercury.lcs.mit.edu> wrote:
Yes, that?s what I meant.
Then you should solder things. Or get one. I finally broke down and got a ratchet crimp
tool. Spent $50 on it at least, probably a bit more, but I have never regretted the
investment.
Right. A good crimp connection is nearly as strong as the wire.
paul
...
If it?s crimped properly, everything is compressed together. Stranded wire has gaps
between the wires, but crimping closes those up. And the connector is forced into the
crevices between the strands.
Solder helps keep things mechanically sound, but
for high current
connections a well executed crimp is probably better.
Really? I thought that while AC was carried in the skin of a conductor, DC was
carried spread evenly throughout, so I assume(d) that the wider cross-section
of a soldered connection would allow it to carry more current.
Perhaps the industries that stopped using soldered connections in favour of
crimped did so because with hand-soldering, you can get variation (and also
of course bad solder joints), whereas with a crimp it's pretty uniform from
joint to joint?
Could be. Speed is also a likely consideration. And with crimp you don?t have to worry
about insulation damage due to heat.
What I would do is pull the old lug off, clean
off the wire, and crimp
on a new lug
Ah, to make sure I understand, you're talking about replacing the terminal
attached to the wire, right? (I tend to think of the 'lug' as the
spade-shaped thing soldered onto the board.) with a good quality (commercial grade, not Radio
Shack) ratchet crimp
tool.
And if I don't have such a tool? ? If it's done right it should be on very
tight; if you can pull it off
without serious force it's either the wrong size lug or the wrong tool.
You're talking about the wire into the terminal here, right? Yes, I've
always made sure a crimped wire _cannot_ be pulled loose (whatever size
connector). 
15 Sep
15 Sep
7:13 p.m.
If it?s crimped properly, everything is compressed together. Stranded
wire has gaps between the wires, but crimping closes those up. And the
connector is forced into the crevices between the strands. >
With a properly done crimp, I think the pressure should be enough to give a
cold wled between the wire and the terminal tag.
Perhaps the industries that stopped using
soldered connections in favour of
crimped did so because with hand-soldering, you can get variation (and also
of course bad solder joints), whereas with a crimp it's pretty uniform from
joint to joint?
Could be. Speed is also a likely consideration . And with crimp you
don?t have to worry about insulation damage due to heat. And if I
don't have such a tool? ?
Then you should solder things. Or get one. I finally broke down and
got a ratchet crimp tool. Spent $50 on it at least, probably a bit
more, but I have never regretted the investment.
12:19 p.m.
On Sun, 14 Sep 2014, Noel Chiappa wrote:
Given how the vinyl has browned, it certainly could have gotten hot enough
to damage the solder connection between the tab and pc board. The opposite
is also true...if the soldering on the tab was bad to begin with, at
higher current levels, it could have gotten hot enough to brown the vinyl
on that terminal.
If you look into the end of the connector, there would be a secondary
crimp grabbing the wire's insulation. Given the pattern of browning on the
vinyl, I think they did use a terminal with a proper insulation crimp, but
it is hard to tell for certain from the photo. You won't find those type
of terminals at the local home improvement store, but electronics supply
companies stock them.
If it were me, I would replace both, but I have the tools for most sizes
of solderless terminals. Tab terminals such as this are very cheap, so I'd
replace it rather than be concerned that the heat might have damaged the
plating or softened the brass. At the very least, the pc board mount tab
should be resoldered.
There is always the surplus market for secondhand tools ;)
Unfortunately, if the wire in question really is 12 or 10 AWG, the OEM
crimp tool required for those yellow terminals is a single purpose tool
made specifically for 12-10 sized terminals vs one intended for say
22-18(22-16) and 16-14. Your second best option would be an
interchangeable die type crimper, but you'd need to be careful to get the
die set intended to crimp terminals with an insulation crimp (sometimes
called a commercial terminal die).
From: Tothwolf
The large yellow terminals are rated for 12-10 AWG wire, so it should in
theory be capable of 20A. Can you tell what size the wire is? Maybe they
used too large of terminal for the wire and the crimped connection is bad?
What caused the excessive current draw though? Is
there a marginal part
on the pc board? You shouldn't be seeing that much current draw though
a pc board.
I realized after I posted is that your first question is the $64K
question - and I don't know the answer. I suppose it could (broadly) be
one of four things:
- The previous owner tried to draw too much power (although the boards
that were plugged in when I bought it shouldn't have done that - I haven't
sat down to calculate the total draw, and compare it with what the PS can
supply, but the card cage was less than half full of stock items)
- There's a fault (e.g. partial short), or faulty component, somewhere
in the power supply
- The connector is under-specified for the current it could be/was asked
to carry
- There's a poor connection somewhere in the connector system, further
dividable into:
-- The wire<->terminal joint
-- The terminal<->lug joint
-- The lug<->PCB joint
I agree that without knowing the original cause, and correcting it, the
problem could recur - but I don't think I can (at this remove) work out
which one it was. So I can take some corrective action(s), but I don't
think I can be sure I got the orignal cause... The first
question that comes to mind for me, is the terminal even
original to the chassis or did someone replace it at some point in the
field?
Well, I'd have said 'original' (it has the look/feel of original work),
but looking closely, I cannot be sure. It's the only connector of that
type in the PS - the other +5V lines are i) soldered to the tips of the
rectifiers in the full-wave bridge, and ii) use crimped bolt-on type
terminals (i.e. not the push-on tabs) for the rest. Those latter do have
the same colour and general look as this one, _but_ the crimping marks
on their insulators are more distinct. (Perhaps the heat removed them on
this one?)
If it was a poor wire<->terminal connection, could that really have
melted the solder on the lug<->PCB joint? Is that
terminal a dual crimped type with a separate insulation crimp?
Sorry, how would I tell? The .250 tab
type terminal on the board is likely made by either AMP or
Molex and would probably be pretty easy to source as a replacement
part.
I read this to mean you think I should replace the soldered on tab
(presumably as well as the crimped terminal on the wire)? Done
correctly, using the right compression dies and tools, crimped
connections are always far more secure and reliable both mechanically
and electrically
Alas, while I have a fairly well-equipped shop, it doesn't run to the
right compression dies and tools...
3758
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3759
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6 comments
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participants (5)
-
ard＠p850ug1.demon.co.uk -
jnc＠mercury.lcs.mit.edu -
paulkoning＠comcast.net -
scaron＠umich.edu -
tothwolf＠concentric.net