What's the problem when a solder joint is only good when the solder is hot?

[wkrantz7]

I've got a strange problem with my tone pot. It doesn't function at all, unless I've just heated the solder. In other words, when I properly solder the connection between the switch to the middle tone pot, it works for like a minute, and then stops, as though the connection doesn't work. So the connection is only good when the solder is hot. I think I'm soldering it properly..what is the problem here?

[wkrantz7]

I think I figured it out. Some of the solder I used dripped onto the arm of the terminal on the potentiometer, and I think its shorting the terminal. When I heat the arm the connection goes back to good, so I am going to try and clean the pot arm.

[wkrantz7]

The attempt to clean the pot arm has been unsuccessful-- the connection only works after I heat the arm. I think I may have to get a new pot, unless anyone has any ideas.

[twotimingpete]

replace the pot!

[Angry Grimace]

Aren't pots like 3 bucks?

[jrockbridge]

It's VERY easy for pots to get damaged. Heat can warp the metal within the pot. Unfortunately, once the metal warps, the pot doesn't function properly. Typically, a warped pot will sound scratchy or may cut in and out. Or, it may not work at all.

 

The metal within your pot probably changes shape slightly when heated. It just happens to make a connection which disappears when cold. The pot should be replaced. But, make sure not to overheat the new pot when soldering. I like to use something metal touching near the solder joint as a heat sink. A heat sink will help minimize heat to the pot while soldering it, so that it won't warp or get damaged.

[wkrantz7]

Hey guys-

The advice to replace the pot would definitely have worked. However I decided to get a little bit creative in fixing the problem. I found that in an exact spot in the middle of the arm of one of the terminals, the current was shorting out if not heated. So I soldered a tiny wire from the end of the arm to the beginning of the arm when it meets the body of the pot, and it works perfectly now. Replacing the pot probably was the best method, but I think this solution is good for now.

[twotimingpete]

people will go to great lengths to save (literally) a few bucks.

[wkrantz7]

people will go to great lengths to save (literally) a few bucks.

Hey, I was proud of my solution! haha.

In retrospect, I think pots from Warmoth may not be the best way to go. The one in question showed 215k ohms on a multimeter (should be ~250k) and on two pots, the pot came loose from the casing when the metal clamps gave way when I tried to insert the knobs on the pot. Not sure if thats a common problem, but I had to reclamp the case back and hold the pot in place with one hand while getting the knob on with the other.

[docjeffrey]

I have a box full of pots of various values in my parts bin. I always buy extras when I have a project going--same with caps, fuses, resistors, tubes, etc. I just double my order because I know I'm gonna need them eventually.

[Bob411]

I have a box full of pots of various values in my parts bin. I always buy extras when I have a project going--same with caps, fuses, resistors, tubes, etc. I just double my order because I know I'm gonna need them eventually.

That's what I do now. Don't want to say how long it took me to figure that out. Save on shipping, don't have to wait when you get another guitar.

Guessing it's not the 2-3 dollars for a new pot, it's waiting over a week for a new one.

[Ratae Corieltauvorum]

You know, I had exactly the same problem with a Gibson R8 neck pickup, immediately aftre soldering it was fine, then it'd crap out, turned out to be a dry joint at the pickup end...go figure:confused:

[ashasha]

Hey guys- The advice to replace the pot would definitely have worked. However I decided to get a little bit creative in fixing the problem. I found that in an exact spot in the middle of the arm of one of the terminals, the current was shorting out if not heated. So I soldered a tiny wire from the end of the arm to the beginning of the arm when it meets the body of the pot, and it works perfectly now. Replacing the pot probably was the best method, but I think this solution is good for now.

Nothing wrong with fixing something instead of replacing it if it works.

As for the value being a bit low, pots are a crap shoot sometimes and tolerances can vary between 5% for good ones and 20% for cheaper ones. Your pot is within 10% and a new pot may not even be that close out of the package.

[Artslinger]

^^^

Thats correct, you can buy pots that have been tested for tolerances but they will cost you more.

[Angry Tele]

buy a multi meter and test them yourself...I like mojo CTS with teh dimple, they are most like the stock AVRI Fender pots that turn very easily. No two CTS are the same I found.

[SteinbergerHack]

In retrospect, I think pots from Warmoth may not be the best way to go. The one in question showed 215k ohms on a multimeter (should be ~250k)

 

 

That's only about a 14% difference, and I would expect the pot to be a 10% item. Also, how good is your meter? Unless it's a Fluke or a pretty serious bench meter, you'd be lucky to get 5% accuracy from it; most of the $25-50 meters out there aren't really meant for accurate readings - they get into the ballpark of the value, but that's about it.

 

In short, I wouldn't take that reading to mean that the pot is bad - it might well be within the stated tolerances.