TECH GURU's out there, how to clean Circuit Board?

Be careful about alcohol, and any other cleaning agents.
In building inertial guidance systems for ballistic missiles we found that the best fluid for cleaning circuit parts is Freon. We used it for decades. Concern for the Ozone layer forced us to abandon Freon except for a few very critical processes.

After a research project lasting several years it was determined that a Citrus-based cleaner was next best. Since we discovered this many citrus-based cleaners for general home use have appeared on the market. I do not know if these are the same as what we now use for circuitry.

Your best bet is to find out what product is now sold specifically as a Freon substitute for electronic part cleaning.

.Davehrab...IKYC*

* I know your coordinates!
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Timrhu...Contact cleaner is for contacts! Some electronic parts will not take kindly to such treatment. (Don't ask how I know). I know Freon is safe, but you can't get it. I know that a safe Freon replacement cleaning fluid exists, and I wish I could give you the name of the stuff. Do some research.