ICOM VHF Caputz?
- Thread starter Jack
- Start date
Yep.. exactly right. The wiring diagram shows a 10 amp fuse and if this was installed correctly and the OP hooked up the polarity backwards, the only damage should be a blown external fuse - easy to fix. Easy to confirm also by just checking to see if 12 volts is getting to the radio. If you have 12 volts to the radio and it doesnt work.. some bad stuff likely happened internally to the radio.
That protection diode is normally reversed biased and never even turns on unless the power input polarity is reversed. I think the diode is only rated for 3 amps but that is steady state and and can likely take a lot higher current for a short period of time which is the case where the fuse blows.
Updated: Not sure about your question. Can you please clarify?
In this case the radio did get a surge of reverse polarity; and, then I thought that if the diode did it's job, the 3 amp in-line fuse would blow. The diode might then be spared; however, if the fuse didn't blow quickly enough, then I thought the diode would "take one for the team" and be damaged, but protect the circuits within the radio.
I thought the way it's supposed to work is: The diode is protecting principally against only reverse polarity? It has (almost) no resistance against correct circuit polarity flow; and, (almost) complete resistance against reverse flow. The fuse is supposed to blow when the circuit is "blocked-up".
In this case the radio did get a surge of reverse polarity; and, then I thought that if the diode did it's job, the 3 amp in-line fuse would blow. The diode might then be spared; however, if the fuse didn't blow quickly enough, then I thought the diode would "take one for the team" and be damaged, but protect the circuits within the radio.
I thought the way it's supposed to work is: The diode is protecting principally against only reverse polarity? It has (almost) no resistance against correct circuit polarity flow; and, (almost) complete resistance against reverse flow. The fuse is supposed to blow when the circuit is "blocked-up".
Here is the spec on that reverse protection diode https://www.digchip.com/datasheets/parts/datasheet/740/DSA3A1-pdf.php
It has a one time surge current rating of 120 amps.
It has a one time surge current rating of 120 amps.
I think this is correct.. The reverse polarity protection diode and the fuse work together for the case of accidental reverse polarity. The fuse may have other purposes, we dont know. We normally think of fuses to protect the wire in the case of a short but this is a great example of another function. If that reverse polarity diode did blow because someone intentionally left out the fuse, I think there are potentially many circuits in the radio that are likely fried.
That is correct.
That is not correct. What would happen is that if there was no fuse, or it didn't blow quickly enough, the diode would blow, at which point you would then have the full reverse polarity voltage from HV to GND, damaging the downstream circuits.
That is correct, except I don't know what you mean by the circuit being "blocked up." The fuse is supposed to blow when the diode conducts, and since that path has little resistance, enough current flows to blow the fuse quickly.
I also have a 422. That thing on the drawing is the female bullet connector as was said. the fuse is an inline glass fuseholder further down the power wiring harness.
