Garmin VHF power issue

[scrotty]

Hey all, I have a Garmin VHF in my boat that has been working fine thus far. I last used the boat and have traced an issue back to it. When connected to power it is blowing fuses instantly. I have removed it from the boat and when the power wires are connect directly to battery posts it shoots out sparks and just can't be connected. Any ideas?
Cheers

[scottar]

Most radios use diode protection as a means of preventing further damage (by blowing the fuse - hooking up direct to a battery if something is blowing a fuse isn't a great idea) The diode will typically fail if a reverse polarity condition has been present (even for a split second) and in most sets if an over voltage condition has been present (same deal with the the time frame). When the diode fails it creates a short circuit across the power input which causes the fuse (and any subsequent fuses until the diode is replaced) to blow. Hooking the radio directly to the battery without a fuse while in this condition can cause the printed circuit board to be damaged if it is the "next weakest" current carrying device.

[scrotty]

Cheers Scottar, it was fused when connected straight to battery. Thanks for your reply.

[TheRealPoMo]

Shorted diode would be same as a working diode provided polarity correct tho? Unless it was a zener that gave overvoltage protection. Even then I would think no difference. Anyways Scrotty - she's stuffed mate. They don't repair these things - buy another.
Not trying to be a smartarse Scottar; always happy to be re-edumucated if I am wrong.

Sent from my SM-G900I using Tapatalk

[scottar]

Shorted diode would be same as a working diode provided polarity correct tho? Unless it was a zener that gave overvoltage protection. Even then I would think no difference. Anyways Scrotty - she's stuffed mate. They don't repair these things - buy another.
Not trying to be a smartarse Scottar; always happy to be re-edumucated if I am wrong.

Sent from my SM-G900I using Tapatalk

They aren't in series - they are put across the inputs to complete a circuit in a reverse polarity situation and thus create a short to blow the fuse. In the process they usually destroy themselves though. If it is just a polarity diode and someone has any sort of soldering skills it's not a huge job. We did repair them when I was at Trymax - cheaper than a new one if that's all that was wrong. Give the boys a call - at least worth asking.

[scrotty]

I'm pretty handy with most things so I opened it up to have a look. I can't see anything obvious to me but I really don't know what the damaged diode would look like anyway? Might just do the modern thing and throw it away and buy a new one?
Cheers for info guys.

[TheRealPoMo]

They aren't in series - they are put across the inputs to complete a circuit in a reverse polarity situation and thus create a short to blow the fuse. In the process they usually destroy themselves though. If it is just a polarity diode and someone has any sort of soldering skills it's not a huge job. We did repair them when I was at Trymax - cheaper than a new one if that's all that was wrong. Give the boys a call - at least worth asking.

Thanks Scottar, makes sense.

Sent from my SM-G900I using Tapatalk

[Fed]

My diode leaks and get this, it's before the on/off switch on the radio so I have to disconnect the battery or it will go flat in a Month or so.
Having said that scrotty, try connecting the radio with the switch turned off and if it still blows a fuse my money is on the diode being short circuited... SNIP!

[scrotty]

Hey Fed, yeah she still blows. I would replace the diode but I don't know which one it is? Cheers

[scottar]

My diode leaks and get this, it's before the on/off switch on the radio so I have to disconnect the battery or it will go flat in a Month or so.
Having said that scrotty, try connecting the radio with the switch turned off and if it still blows a fuse my money is on the diode being short circuited... SNIP!

Before the switch is normal for radios at least Fed. Can't ever recall seeing anything different.

[Fed]

I don't do radios scottar they work on magic IMO.

I would replace the diode but I don't know which one it is?

It would have to be between the power socket & the on/off switch scrotty, wired straight across the positive & negative. I don't think you would have to replace it, just cut it out, scottar?

[scrotty]

There is a little blue barrel looking thing soldered across the positive and negative where the power lead is soldered to the board?

[scottar]

It will work without it but is probably a zenor for overvoltage protection as well and really should be replaced.