[R-390] Thoughts on Pots

[Drew Papanek]

Hello,

Here is some of my input on the topic being bandied about...

 >What are you guys using to clean and take the noise out of carbon 
potentiometers?

I squirt in 100% isopropyl alcohol with an eyedropper.  If one treatment 
does not clean it, two almost always does.

A readily available source of the alky is isopropyl gasoline dryer.  Get the 
kind that says "isopropyl" and does not call out any additives.

Alternatively, one might try using 100% pure ethanol, available at  local 
liquor stores as "Grave's Grain Alcohol".  It is not as good a solvent as 
the isopropanol and probably won't work, but one can then soothe the 
resultant frustration by drinking the ethanol :o)

>However, I have had some success disassembling badly worn pots and
>adjusting/bending things to get the wiper to contact an unworn part of the
>carbon comp.

I did that once with the airflow sensor on a friend's car (Mazda).  The 
airflow sensor is a pot mechanically coupled to a spring-loaded vane in the 
engine's air intake.  Moving the wiper to an unworn portion of the 
resistance element and then cleaning with isopropyl alky cured an 
intermittent lean mixture problem (engine sputtered) at certain RPM / load 
conditions.

>Anybody else ever do this, or am I the only one. It ain't the money ;-)

I'm as much or more a cheapskate than anyone else, but it was worth 
tinkering to escape paying about $400 for a new airflow sensor!

>Chuck Rippel recommends replacing the S-meter zero pot on the IF deck with 
>a new, ten turn, >precision potentiometer of the same value.

David Wise some time ago came up with a simple mod involving adding a couple 
of resistors and moving a wire or two around on the pot connections.  I 
added that to my unit and it works great; lets you keep the original pot.  
Search the "Pearls of  Wisdom" at r-390a.net for his posting.

Drew