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cables d tap p tap solder

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#1 Noah Graham

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Posted 23 June 2016 - 05:32 PM



I'm new to the Forum so I hope I'm not repeating an already existing topic.


I have a p tap to lemo cable that has a lose connection and needs to be re-soldered on the p tap end.  I just want to make sure I know what I'm getting into before I go ahead and solder it.  Is there a specific type of solder I should use?  I know the polarities can be reversed, so is there anything I should be aware of while soldering to avoid this?  Any other advice to help me successfully complete this would be greatly appreciated.




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#2 Tom MaCoy

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Posted 24 June 2016 - 10:23 AM

Welcome aboard.


How much soldering experience do you have? I'm reasonably handy with an iron, enough that I've done a few Lemos myself, and (while I'm sure there's many more experienced hands who can say differently) they can be a right pain in the ass. However, if you're only doing the P-tap side, it's a fairly simple operation. 


I can't speak to a specific solder; mine have all held together fine with common old 60/40. For the polarity, P-taps usually have a stamped label indicating +/-; I usually outline mine in gold/silver sharpie so I can tell at a glance while working. If you pop open the P-tap and find colored wire, black is almost always ground (-) and red is positive. This isn't a guarantee though, so you'll want to mark/photograph which color wire ran to each side of the P-tap. (If both wires are black, a streak of gold sharpie or red heat shrink is a good way to permanently mark the +.) When you get into the P-tap, re-solder the pin farthest from the entry first; get it in place, then cut the other wire back a little to fit the near pin. Once you're soldering's done, assuming the Lemo is the feed side, plug it in and check the P-Tap probes with a multimeter before you plug it into anything; black side to -, red side to +, and make sure it's giving you 12/14.4 or whatever volts your battery puts out. 


I'm sure there's some pro details that a really experienced hand could give you, but that's the basics that have worked for me so far. 

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#3 Andrew Payne

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Posted 24 June 2016 - 11:48 AM

Those are good tips.
Solder type doesn't matter really, although I would opt for lead free.  It takes a little more heat to melt, but a decent iron (~$20) will do the job.
If at least one of the two wires is still connected to the p-tap, you can tell your polarity.  Some cables have flecks or stripes which indicate the positive wire.  Some are red and black where black is your negative.
1 - remove the old solder.  There are little air pump devices that can be used to suck up the old solder, just melt it and vacuum it up.  It needn't be perfectly clean.
2 - prime the wire end.  Clip the the "dirty" ends off, strip about 1/8" of the sleeve off.  Twist the wires clockwise to make them compact, heat them with the iron, and melt a little solder onto them (separately).
3 - prime the terminal.  Same deal, heat the contact on the p-tap where the wire connects and melt just a little solder on it.
4 - connect.  Heat the contact area to liquify the solder on there, press the wire in and let it all melt together.  It's important for the contact to be hot to avoid a "cold" joint (i.e., a bad connection).
Avoid using too much solder.
Although you need to get the metal hot for the solder to make a good connection, be careful not to melt the plastic parts of the connector.
P-taps are polarized as mentioned above, so just look on the connector for plus and minus.


If it's your first time, practice first.  It's not complicated, but it takes practice.

Edited by Andrew Payne, 24 June 2016 - 11:50 AM.

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#4 Ramon Engle

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Posted 19 July 2016 - 10:23 PM

Hi guys. Just chiming in on the cable making thread.

After years of making my own cables for my steadi gear, prestons and everything else you can imagine I found a soldering station that is fantastic.


Weller WD 1000m


It's one of the few units with a soldering PEN. Pen being the operative word here. It's not an iron so to speak. The tips are quick to change and come in a variety of widths and styles. The pen sits in a magnetic cradle that senses the pen and drops the temp to below 100 degrees so not to burn out the tip.

There are 3 temperature presets which is handy when switching from less sensitive work to the finer tasks.

For years I lived and died by the Hakko 936. Great piece of kit and I was not a weller fan at all. But this gear has become the workhorse of my work bench. I love.

I also made a set of locking helping hands with two magnetic based noga arms which were originally designed for precision measurement.

Its a cool set up.

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#5 axel ebermann

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Posted 20 July 2016 - 08:02 AM

I have a Weller too. LOVE that thing.

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#6 Ericthegreat


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Posted 06 September 2016 - 02:48 PM

I have a Weller too. LOVE that thing.

I second I mean . . . Third this! :) Great product indeed.

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