Flakey Molex(?) connectors

[Bob Engelhardt]

Part of my Habitat volunteering has involved repairing their power
tools. They get Milwaukee tools from the Milwaukee refurb/repair
facility, through a Milwaukee charitable program.

A common problem with these tools is the trigger. Which, of course,
isn't just a switch but is the trigger with 4 control wires as well as
the 2-in, 2-out power lines, a tiny PCB, and the battery connector -
also with control wires. I.e., a nightmare to diagnose and sometimes
ends with us junking the tool (a new switch assembly is much more than
what we pay for the tool).

I was able to definitively diagnose the current tool's problem as a
flakey connector on the signal cable between the battery and the PCB.
The connector appears identical to the ones used for running PC fans
from the MoBo. Like this:
https://i.imgur.com/Q7kfqQG.jpg

I found these contacts that look to be identical to the ones in the tool:
https://www.digikey.com/product-detail/en/molex/0560868000/WM11257CT-ND/5287249

I'm puzzled that Molex connectors, if that's what they are, can be so
unreliable. And that Milwaukee would use such unreliable connectors.
Has anybody else seen problems with these connectors?

Bob

BTW - I fixed the tool by removing the contacts from the shell and
soldering them to the pins on the board.

[John Robertson]

If these connectors are accessible to end users, then it may be as
simple as they are cycled (removed/repluged in) beyond the Molex specs
for life cycles. Usual life cycles are under 100 insertions, however I
can't find the life insertion data on those pins, other than some info
on thirty cycles.

http://www.molex.com/pdm_docs/ps/PS-505261-001-001.pdf

Also these pins are rated at 2A max, any chance they are drawing more
current or running at that current - which shortens the life of course.

Other problems can be in correct crimping tool leading to slight
looseness in the crimp to wire, which ends up as a problem. If the
connector is stressed or can be flexed that will lead to trouble.

I've been using Dow Corning #4 Dielectric Grease on connector pins for a
number of years now (over 20 years) and I find the connections last much
longer and run cooler compared to the same Molex connectors on the
identical equipment.

John

[Bob Engelhardt]

On 6/15/2019 4:09 PM, Bob Engelhardt wrote:
> ...

> I found these contacts that look to be identical to the ones in the tool:
> https://www.digikey.com/product-detail/en/molex/0560868000/WM11257CT-ND/5287249

> ...

Wait ... that's the pin, the contact:
https://www.digikey.com/product-detail/en/molex/0593708100/WM12256-ND/3263485
(the "Drawing" link has all the details).

[Jeff Liebermann]

Yes, but not in power tools. I've had to deal with intermittent
square pin connectors in commercial 2-way Motorola radios and
repeaters for quite some time. Motorola used larger versions of the
connectors to interconnect PCB's to backplanes during the 1970's and
1980's. In general, they were fairly reliable. However, they were
not perfect. Occasionally, I would get a repeater that had an
intermittent connection. After manual percussive remediation (beating
on the box with a rubber mallet) the repeater would fix the
intermittent connection for a few months, when the problem would
re-appear. Sometimes, sliding the PCB's in and out would fix the
problem, but sometimes the intermittent would re-appear on another
pin. Contact cleaner or Cramolin did nothing useful. It was quite
maddening.

Motorola apparently also knew about the problem and later switched to
round stake pins in the PCB, with matching square receptacles. That
worked well and there were no intermittents. It also provided me with
an important clue as to the cause of the problem. Take you best guess
now, and continue reading.

I eventually decided to analyze the problem. When the next Motorola
repeater failed, was careful not to jar or move the box, an found the
intermittent pin and socket. I removed the PCB and carefully
inspected both under a microscope. Sorry, no photos.

The edges of the square pin had a burr along two adjacent edges. Like
the rest of the connector, the square pins and burrs were duly tin
plated, making this a manufacturing defect. Instead of making contact
on the allegedly flat side of the pin, contact was being made to the
sharp edges of the burrs. These sharp edges would initially make
contact, but did not have enough surface area to handle much current.
An amp or so would cause them to burn off the plating and expose the
underlying copper. The copper expanded when it started to arc, moving
the pin away from the side of the receptacle and breaking the
connection. It was difficult to see the problem, but the presence of
a burr, with microscopic dark black spots along the sharp edge of the
pin and along the flat part of the receptacle, were sufficient to
assign the blame.

In the case of your power tool, the problem might have been an
"insulation crimp" where the wire was crimped to the receptacle by the
insulation instead of the exposed copper. This sometimes happens when
the wire was not properly stripped and insulation is still on the end
of the wire.

>BTW - I fixed the tool by removing the contacts from the shell and
>soldering them to the pins on the board.

Yech. Whatever works.


--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[N_Cook]

Assuming not failed crimp/s , with needle nose pliers , I put a set on
every other pin, not enough to negate mating of course

[Bob Engelhardt]

On 6/15/2019 5:04 PM, John Robertson wrote:
> If these connectors are accessible to end users, ...
> Usual life cycles are under 100 insertions, ...

Highly inaccessible. I hadn't thought about life cycles - it's
something to keep in mind.

> Also these pins are rated at 2A max, ...

They're just control wires - ma's likely.

> I've been using Dow Corning #4 Dielectric Grease on connector pins ...

I'd like a conductive grease. Pack some in the connector pocket & let
grease make the connection. Except if it leaks out, it wouldn't be good.

Thanks,
Bob

[Bob Engelhardt]

On 6/15/2019 7:40 PM, Jeff Liebermann wrote:
> ... I've had to deal with intermittent

> square pin connectors in commercial 2-way Motorola radios and

> repeaters for quite some time. ...
>
> The edges of the square pin had a burr along two adjacent edges. ...

It must have been very satisfying to find the smoking gun. Or the
smoking edges in this case.

Even if there wasn't a burr, a slight misalignment would make the pins
contact on their corners iso the flats.

>> BTW - I fixed the tool by removing the contacts from the shell and
>> soldering them to the pins on the board.
>
> Yech. Whatever works.

Frankly, I didn't have much choice, given my limited equipment and
skills. Even replacing the contacts would have meant making a crimp
connection smaller than my means to.

Thanks for your reply,
Bob

[Bob Engelhardt]

On 6/16/2019 11:09 AM, N_Cook wrote:
> Assuming not failed crimp/s , with needle nose pliers , I put a set on
> every other pin, not enough to negate mating of course

I love it! That is perfectly "KISS". I'll be getting more tools with
this problem and that is how I'm going to fix them. Thank you!

Bob

[legg]

On Sat, 15 Jun 2019 16:09:17 -0400, Bob Engelhardt
<BobEng...@comcast.net> wrote:

If they're tin plated, they are not good for small signals. The
contact surfaces can usually be restored by simply pulling and
reinserting the connector a few times. Square pins can be brushed
clean. The problem will reoccur. It can be agravated by mixing tin
with gold flash (pins vs receptacles. Sometimes the gold flash in the
receplacles is local and hard to identify.

Depending on humidity and temperature levels, the tin/tin contacts are
good for between 6 and 10 years, between cleanings.

RL

[mako...@yahoo.com]

>
> If they're tin plated, they are not good for small signals. The
> contact surfaces can usually be restored by simply pulling and
> reinserting the connector a few times. Square pins can be brushed
> clean. The problem will reoccur. It can be agravated by mixing tin
> with gold flash (pins vs receptacles. Sometimes the gold flash in the
> receplacles is local and hard to identify.
>
> Depending on humidity and temperature levels, the tin/tin contacts are
> good for between 6 and 10 years, between cleanings.
>
> RL

google "fretting" corrosion.

can be insidious to troubleshoot

mark

[John Robertson]

Thanks for that info - I went to one link:

https://www.windpowerengineering.com/mechanical/bolts-and-bolting/how-to-recognize-fretting-corrosion-and-what-to-do-about-it/

where they talk about fretting corrosion in wind turbines. Even when
there is lubrication fretting corrosion occurs, but it is more benign
with lubrication as opposed to no lubrication.

So I suggest folks look at something like Dow Corning #4 dielectric
grease for connectors that experience any vibration to increase the MTBF
of the connection(s). I know DC#4 helps my games run longer between
service.

Others swear by De-Oxit, but the resulting contact protection is
probably similar.

John :-#)#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

[legg]

On Tue, 18 Jun 2019 07:51:07 -0700, John Robertson <sp...@flippers.com>
wrote:

That's a mechanical failure in iron-bearing materials.

The small signal electrical contact failure is straight oxidation of
tin.

RL

[John Robertson]

I dunno, I've seen a lot of contact failure over the years and fretting
would explain some of what I am seeing. And a product like DC#4 (now
called Molykote) helps prevent failure by providing both mechanical
(friction reduction) and electrical protection:

https://www.dupont.com/content/dam/Dupont2.0/Products/transportation/Literature/TDS/10-1187-01.pdf

John :-#)#

[legg]

On Tue, 18 Jun 2019 08:38:13 -0700, John Robertson <sp...@flippers.com>

Contact coatings are useful when non-optimal materials benefit from
protection from oxygen, but small signal connections are best achieved
just using the right materials. Tin isn't the right material.

RL

[John Robertson]

I'd like to argue with the manufacturers, but they stopping making the
games we fix back in the mid to late 90s...so I'm stuck with tinned
contacts and trying to extend their useful life.

John :-#)#

[N_Cook]

Whenever I have to separate such a connector, whatever the problem may
be, I do this alternate pin set business.

[Ron D.]

Tin-Tin connections can be a problem in moist environments. Gold flash is preferred. You could try to plate them. I had to use electroless gold and boil the items in baking soda to remove the OEM flux for a high temp application at work.

I also use Conducto-lube at home. Also an expensive option.

[Lucifer]

On Tue, 18 Jun 2019 17:24:44 -0700, John Robertson <sp...@flippers.com>

What about wire wrap and insulation displacement connections?

>John :-#)#

[John Robertson]

No wire wrap used in our commercial games, but an EPROM copier I made up
back in the 70s worked when I last tested it in the late 90s. It is
sitting in a drawer but unlikely to be used again as I have much better
tools these days.

Insulation displacement? Don't make me laugh - those are quite the pain
over crimped Molex pins. Lots of failures with power connectors on the
insulation displacement connectors. Seemed to be related to the pin
tension - they didn't grab the pin as well as the original design,
certainly not as well as Trifurcon pins.

John :-#(#