[R-390] What is on the 390 chassis anyway

[Tisha Hayes]

The yellowish tinge of the aluminum can come from a couple of things;

1. It can be MFP (moisture and fungus protectant); a type of varnish.
Usually you will see it coating lots of things and not just the aluminum.

2. It can be aluminum yellow chromate. This is a electrolytic treatment
that was done to many aluminum items in the military and avionics
industries. It is no longer available as it used "hexavalent chromium" to
create the coating. It "passivates" the aluminum, sort of like a controlled
corrosion up front to keep uncontrolled corrosion from setting in later. It
has a golden look to it. The original process was toxic as hell and is no
longer possible using the same technique.

3. It can be fifty years of cigarette smoke residue.

409 spray cleaner will not remove MFP or aluminum yellow chromate, it will
cut through dirt and cigarette smoke residue.

If you get aggressive with solvents you can remove the MFP. If you get
aggressive with abrasives you can remove the passivated layer of aluminum
yellow chromate. You really do not want to take the radio all the way down
to bare, shiny aluminum unless you plan on waxing, varnishing or painting
it again.

I have succeeded in restoring the MFP and the yellow chromate look with
spray varnish. It (mostly) looks the same and provides at least some
corrosion resistance.

If you are re-finishing aluminum front panels you probably need to primer
the aluminum of you used stripper or a mechanical means to take it down to
shiny metal.

-- 
Ms. Tisha Hayes. AA4HA

*""It is not because things are difficult that we dare not venture. It is
because we dare not venture that they are difficult." -Seneca"*