[R-390] Cleaning pots

[Barry Hauser]

While we're on the subject --

Joe W2DBO wrote:
>I usually disassemble em and clean the carbon with, hate to say this but 
>what ever I have on hand, have used alcohol, ordinary contact cleaner etc.

If you have them opened and can see what you're doing, you can test whatever 
cleaner on a non-critical part of the carbon to be on the safe side.  I 
personally have never dissolved the carbon.  Might not require any cleaner, 
but just a wipe-down.

> Clean the wiper, small drop of very lite oil on the shaft, put it back 
> together and its as good as new.

That is if the wiper track is not badly worn.  Sometimes it isn't worn 
through, but rough enough to continue to cause intermittents.  While you 
have it apart, you can check for this as I previously noted.  Often you can 
"re-track" the wiper with the pot still mostly assembled -- shaft still in 
place.  Or you can remove the retainer and back out the shaft and wiper 
assembly.  If the track looks good enough, don't attempt to re-track it. 
Make sure the tension on the wiper is adequate.

>Squarting a shot of cleaner into the pot is usually a temp fix.

Agreed.  Often all you're doing is redistributing the debris and it has a 
way of migrating back -- if you didn't make it worse in the first place.  If 
attempting the squirt job, my experience is that it generally takes quite a 
bit of cleaner and two or three treatments, allowing the stuff to drain out 
each time and possibly a final blast from an air can.  Even then it's still 
unreliable because you're basically flying blind.  The tendency is to 
prematurely conclude that the pot is not repairable.

>  I don't for a minute think any contact cleaner will "eat carbon" if you 
> read the ingredients you will find most of em have the same stuff.

I'm going by second/third-hand reporting.  It isn't the carbon, but the 
binder used that varies.  The solvents in contact cleaners also varies. 
Alchohol acts differently than naptha (in DeOxit), etc.  Chances are a wide 
variety of solvents are OK with the pots you'll find in an R-390/R-390A. 
The assumption might be dicier with later vintage equipment, particularly 
consumer stuff.

>  most pots in the 390 are high quality and worth the effort to repair. 
> Thats my story and Iam sticking to it.

I agree.  With the kind of intense maintenance, preservation and repair that 
many list members do, disassembling and restoring a pot is a snap.  One 
tip -- when replacing the cover, carefully bend back the tabs. If it's still 
a bit loose, rather than risk staking the tabs or resorting to extreme 
force, you can apply a little epoxy or other cement on the tabs to secure 
the cover if you like.  (Generally not necessary.)

Again, it isn't the money.  Replacement grade pots are often not of the same 
quality and involve some adjustment and messing around anyway.  Often the 
shaft is of the wrong type -- half-shaft, split-splined, etc.  or missing 
the locking tab (or wrong spot) which keeps the pot oriented on the panel, 
or shaft too long and has to be cut down, and so on.

Barry