In , ojunk
(OZARK333) wrote:

He is correct about the reverse polarity protection diode.

No, he's not. If the diode was shorted, it would have blown the fuse/breaker on
the power supply (or melted something else if the supply wasn't protected). If
the diode was open, the radio would have worked as normal when the power was
connected properly. Neither were the case.

He was measuring from the negative terminal of the power supply to points inside
the radio, where he was getting 12V everywhere. The only way that can happen is
if the negative lead is disconnected. Try it yourself (no, it won't hurt the
radio). What happened is that the reverse-polarity protection diode did it's
job, and did it exceptionally well. When the power is connected backwards, the
diode is supposed to show a short and blow the fuse, but since there wasn't any
fuse it melted a power lead. That's one stout diode!

Anyway, the damage should be minimal, and certainly much less than if the diode
had failed.





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