Originally Posted by jwalker
I understood what you were saying but it makes no sense to do that unless that diode had another purpose or it's simply poor design. Also Diodes normally fail open circuit so it hints at some other device or purpose. The only reason I can think of for that system is if the charge voltage and the internal battery voltage can't tolerate the voltage drop across a series diode. Anyway good luck with it.
Just a thought, if your replacement diode has a higher current rating than the fuse you use then you'll have a better chance of not damaging the replacement.
The only use the Diode has is to protect the radio from being connected the wrong way round.
The diode is wired so the flow of power goes from negative to positive, so under normal circumstances power can not flow as Diodes only allow power through one way.
When you connect the power the wrong way round, it allows the power to flow and will blow the fuse and normally the diode as it has quite a low current rating. (just like connecting a piece of wire straight across the terminals)
Replacing the diode with a higher rating will allow damage to your gear if wrongly connected in the future. You can in theory use the radio with no diode but risk blowing it up if you reverse the polarity sometime in the future!
Hope i have explained how it works in an easy to understand way.. Its probably 25 years since I have had to think about this subject!!