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:
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I found these contacts that look to be identical to the ones in the tool:
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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.
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.
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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.
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.
Yech. Whatever works.
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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.
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.
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.
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 :-#)#
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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:
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.
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.
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.
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.
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