[R-390] Charred chassis cleaning

[John Wendler]

I pulled the audio deck off and spotted the big char mark on the main
chassis underneath.  The mark was like something "hot" broke loose and
partially arced and partially burned.  A mess of carbon and some resin,
perhaps a resistor burnt.  (A previous audio deck; the present one shows no
signs of reciprocal damage.)

Formula 409 did not touch it, neither did Isopropyl Alcohol.

PVC pipe cleaner, on the other hand, worked a treat.  The charred mess
disolved like a drop of ink into a large glass of water.

PVC pipe cleaner is a mixture of things like Acetone and MEK; there may be
other organic solvents depending on brand.

I would not use it near a painted surface or any plastics, but it did a
nice job on the aluminum.

Use only with good ventilation and appropriate chemical precautions.

JPW