- Flakey Molex(?) connectors - 5 Updates
| Bob Engelhardt <BobEngelhardt@comcast.net>: Jun 15 04:09PM -0400 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 <spam@flippers.com>: Jun 15 02:04PM -0700 On 2019/06/15 1:09 p.m., Bob Engelhardt wrote: > 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. 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 <BobEngelhardt@comcast.net>: Jun 15 05:23PM -0400 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 <jeffl@cruzio.com>: Jun 15 04:40PM -0700 On Sat, 15 Jun 2019 16:09:17 -0400, Bob Engelhardt >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? 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 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 |
| N_Cook <diverse@tcp.co.uk>: Jun 16 04:09PM +0100 On 15/06/2019 21:09, Bob Engelhardt wrote: > Bob > BTW - I fixed the tool by removing the contacts from the shell and > soldering them to the pins on the board. Assuming not failed crimp/s , with needle nose pliers , I put a set on every other pin, not enough to negate mating of course |
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