Originally Posted by jwalker
Nor do I understand the comments in this thread re the diode. Normally a reverse polarity protection diode is simply in series with the power supply.
The diode is in parallel with the power supply.
When radio is connected properly current cannot flow through diode as it only allows power to flow one way.
If you connect the supply wrong way round, it allows the current to flow directly across the input causing the fuse and normally the diode to blow - normally quick enough to protect the equipment.
Although you may then connect power supply correctly, the fuse will continue to blow as the diode has "blown" and is allowing current to flow both ways.
Over 30 years or so ago, I used to make a fair bit of pocket money 'Fixing' broken CB radios that had been connected wrongly. (about 1 in 25 were damaged beyond repair, normally because the wrong in-line fuse had been used!)
Hope you can understand this explanation