15 Sep
2014
15 Sep
'14
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...