I have an old, corroded circuit board (I will tell you the full story if you ask, but I thought I'd spare folks an [even more] boring tale) - it was a sealed board, but apparently has a leak somewhere.
The only thing aside from (corroded) bubble micro-switches on the board is a flat strip potentiometer (or so it would appear to be). It's a long flat strip of some sort of material, with taps at both ends, and what appears to be another strip on top (center tap) that is pressed into contact with the bottom strip via a physical plastic slider that has a small plastic ball tip user to apply pressure.
I've been trying to determine the rating (so I can replace it), but since it's sealed, it's kind of hard to address the flat potentiometer itself - I have to just splice into the leads and measure the ratings - the trusty multitester reports the resistance across the ends to be 750 Ohms. I initially took this reading with a grain of salt, due to the corrosion of the board (and even the leads), but measuring off the center tap with respect to either end also seems to yield a range of approx 750 Ohms.
The issue is that any readings I take with respect to the center tap have an additional approximate 5K Ohms added to them - the range is still 750 Ohms, but the center tap seems to be adding additional resistance.
Now the question (finally ;-):
Am I safe in assuming that this extra 5K of resistance is a result of corrosion between the center tap/strip and the underlying strip? Common sense says that no one would bother to manufacture a potentiometer that adds an extra amount of resistance to the center tap, since this would limit the flexibility of the potentiometer, particularly given that anyone who wanted to add extra resistance to the center tap would only have to add an extra 5K resistor in series with the center tap to achieve the same result.
So, can I assume the potentiometer is dirty, and just substitute a generic 750 Ohm potentiometer to replace it? (I already built a 750 Ohm stepping switch, since my local Radio Shack didn't carry a 750 Ohm potentiometer - I just want some additional opinions before wiring everything back together...
Cheers,
-Jon
