itsybitsy frying potentiometers?

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blakebr
 
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Re: itsybitsy frying potentiometers?

Post by blakebr »

Hi,

That is amazing.

Is there continuity between the outer pins and the silvery trace that connects to the resistive race? If it is open, that would indicate a manufacturing defect in the crimping of the pin to the trace.

From the wear marks it looks like the two wipers to the center trace are making connection all the way around. Of the three outer wipers, it looks like only the outer two are making contact to the race. That should not be an issue. The wear marks show that the outer two wipers are making contact with the traces that connect to the pins.

If you can put a small bit of solder between the metal of the pin and the trace to see if that gives continuity? I have a guess that the bit of flux that is getting between the pin crimp and the end trace is expanding as it cools and separating the pin crimp from the trace. It may be possible that the pin metal and dissimilar trace metal are reacting with the flux and forming an oxide barrier between them.

Thank you for your testing.

Bruce

P.S. Picking a background with the exact texture and color amazing. It is playing tricks with my eyes. ;-)

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dastels
 
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Re: itsybitsy frying potentiometers?

Post by dastels »

Can you measure between each outer pin and the outer race just beyond where the pin is connected? what about between the ends of the outer race (beyond the pin and its connection) and points on the outer race? I'm wondering if the problem is the connection of the pin(s) to the race or within the race.

Dave

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blakebr
 
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Re: itsybitsy frying potentiometers?

Post by blakebr »

The small voltage you are seeing is normal. There is always a small leakage that a high input impedance meter can detect.

Bruce

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dastels
 
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Re: itsybitsy frying potentiometers?

Post by dastels »

I wonder if the heavy soldering on to the pin (and the connections to the race) weakened the connection or the race material. Oddly, all the potentiometers like these are the PCB mount style, none with solder lugs. E.g. https://mm.digikey.com/Volume0/opasdata ... 01B1A1.jpg.

Dave

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BasementBodger
 
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Re: itsybitsy frying potentiometers?

Post by BasementBodger »

I probed everywhere on the outer race and couldn't get continuity. Not sure if the soldering is the culprit since everything was working fine on bench power (measured resistance and voltage) and only manifested issues once the itsybitsy was running the show. Also... this is only one of 12 potentiometers that met this fate. Chances of them all failing mechanically are pretty slim.

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blakebr
 
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Re: itsybitsy frying potentiometers?

Post by blakebr »

Dave,

Does adafruit have a procedure where a few of the pots can be returned for an autopsy/ necropsy/ etc.?

Bruce

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dastels
 
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Re: itsybitsy frying potentiometers?

Post by dastels »

In some cases, yes. I'll check about this.

Dave

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dastels
 
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Re: itsybitsy frying potentiometers?

Post by dastels »

Word is to replace them. Solder more carefully, and just to the pins, not up where the races are connected. How many are bad?

Dave

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BasementBodger
 
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Re: itsybitsy frying potentiometers?

Post by BasementBodger »

ok... i gave it one more try, and managed to get it working. i was extremely careful to keep the solder heat as close to the end of the potentiometer pins as possible. i still ended up with one kinda flakey connection on a ground pin that i mostly fixed by crimping down on the pin with some pliers. i guess these pots are just extremely heat sensitive. it's still weird that with some of the other attempts, their function seemed to degrade over time once connected to the board. all told, i bought 15 and used all of them, plus a couple spares i had laying around. it was supposed to be a simple project... haha

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