ICOM VHF Caputz?

Brian D · Jun 2, 2018

Here is the service manual. Haven't looked through it but there might be an internal fuse. Might being the operative word.

https://www.r-onetrading.com/download/icommarine/IC-M422_SM.pdf

Jackdaw · Jun 2, 2018

You probably blew up the internal voltage regulator IC, usually a TI LM-series device. They cannot handle reverse polarity.

Jackdaw · Jun 2, 2018

Looking at the pdf that Brian found, the unit does have a descreet regulator IC. If it blew up and damgaged nothing else, it might be swappable with a little soldering.

http://product.ic114.com/PDF/K/KIA7805_24AP_API.pdf

BigEasy · Jun 2, 2018

Unfortunately for most of us, we don't have the trouble shooting skills to fix a problem like this unless its something simple like an internal fuse. ICOM's present policy (unless under warranty) is a minimum service charge of $92 + parts + shipping both ways. After they trouble shoot and provide an estimate, if you decide not to repair, its a flat $45 service fee + shipping. So its the usual "catch 22" situation. If the radio is several years old, it may be more practical to buy a new one for $250 vs spending a minimum of $130, likely more to repair an old radio. Another option might be to find a reputable local electronics shop, that repairs marine radios, to check it out; however, if the repair is unsatisfactory you may regret your decision to repair. Another facet of DIY electronics repairs is that you may have blown several components and in addition to having the skill set to trouble shoot & repair, you also need the test equipment to ensure that the radio is operating within specs after the repairs are completed. Generally, when I have a problem like this, I usually opt for a factory repair or buy new. Unless its a major expenditure, I usually buy new.

twalker H260 · Jun 2, 2018

I have the same radio and do have an inline fuse. Page 36 of the manual shows how to change it. This assumes it was the factory supplied wiring harness and a P.O. didn’t modify it!

Manual here:

http://www.icomamerica.com/en/downloads/DownloadDocument.aspx?Document=88

The reverse polarity May have damaged the radio without blowing the fuse.

SG · Jun 2, 2018

There is a diode that is intended to protect against a reverse polarity event. I believe, that IF you were were lucky, that's the only part that would need to be replaced.
I think that you'd have to take the radio apart, (as generally shown in the *.pdf below; and trace the power 12 V to the power supply. It isn't shown (except in the diagrams below) in the info from Brian's post; however, I'd call a local real electronics type if you want to take a shot at it.

From Brian's post, I think this it it.
https://www.r-onetrading.com/download/icommarine/IC-M422_SM.pdf

P.S. -- What were you doing with the battery leads in being disconnected with the DC power running through the circuits?
I once fried a Heart Interface by disconnecting the batteries from it and then energizing the AC power. It blew the power regulation board, I'm told. The rep took pity on me and replaced the unit. That was over three decades ago :^))). Shit happens.

walt · Jun 2, 2018

There is a diode that is intended to protect against a reverse polarity event.

Good find.. That diode is intended to work in conjunction with a fuse in order to protect for reverse polarity. I didnt look to see if some external fuse was specified in the wiring diagram but if so, all that should have happened with the reverse polarity is that protection diode forward biased so there was a lot of current flow and this would blow the fuse in an instant. If the proper fuse was used, that protection diode should be just fine.

Ken Cross · Jun 2, 2018

Be warned. You can not legally work on a transmitters in the US without a radio telephone license. Odds of getting caught are slim, but the citation is expensive. There are good reasons for that requirement.

Ken

jviss · Jun 3, 2018

walt said:
Good find.. That diode is intended to work in conjunction with a fuse in order to protect for reverse polarity. I didnt look to see if some external fuse was specified in the wiring diagram but if so, all that should have happened with the reverse polarity is that protection diode forward biased so there was a lot of current flow and this would blow the fuse in an instant. If the proper fuse was used, that protection diode should be just fine.

Walt makes an excellent point. If the reverse polarity protection diode worked as designed, that is, the in-line fuse blew, you would merely need to replace the fuse. If there was no in-line fuse, then the diode probably burnt out, failing 'open,' and then subsequent damage occurred. This could be almost anything connected between HV and GND, and also anything connected to the other side of a component that might fail to a short circuit condition.

SG · Jun 3, 2018

If the reverse polarity protection diode worked as designed, that is, the in-line fuse blew, you would merely need to replace the fuse. If there was no in-line fuse, then the diode probably burnt out, failing 'open,' and then subsequent damage occurred.

The operating manual, plus the service manual seem to say that there is an inline fuse.

Jackdaw · Jun 3, 2018

SG said:
If the reverse polarity protection diode worked as designed, that is, the in-line fuse blew, you would merely need to replace the fuse. If there was no in-line fuse, then the diode probably burnt out, failing 'open,' and then subsequent damage occurred.

The operating manual, plus the service manual seem to say that there is an inline fuse.

View attachment 151337

That looks like the female connector, the pair of the male next to it. They put one of each on the connected pairs to make sure you cannot connect with reverse polarity.

Jackdaw · Jun 3, 2018

Ken Cross said:
Be warned. You can not legally work on a transmitters in the US without a radio telephone license. Odds of getting caught are slim, but the citation is expensive. There are good reasons for that requirement.

Ken

Interesting point. I wonder what that means exactly, one could make the case that it should only apply to actual RF circuitry. Anyone know?

SG · Jun 3, 2018

This is the owner's manual link tha was posted above by TWalker..

http://www.icomamerica.com/en/downloads/DownloadDocument.aspx?Document=88

Isn't that ICOM's graphic for that fuse that I posted above?

P.S. -- The reverse polarity apparently occurred well upstream when the battery posts were inadvertently misconnected.

SG · Jun 3, 2018

Walt makes an excellent point. If the reverse polarity protection diode worked as designed, that is, the in-line fuse blew, you would merely need to replace the fuse. If there was no in-line fuse, then the diode probably burnt out, failing 'open,' and then subsequent damage occurred. This could be almost anything connected between HV and GND, and also anything connected to the other side of a component that might fail to a short circuit condition.

JViss: If the diode failed "Open", then the circuit wouldn't conduct electricity further. It just would have broken the circuit like a fuse.

There are cases where they "fry " and fuse "closed" -- but that's unusual, isn't it?

jviss · Jun 3, 2018

SG said:
Walt makes an excellent point. If the reverse polarity protection diode worked as designed, that is, the in-line fuse blew, you would merely need to replace the fuse. If there was no in-line fuse, then the diode probably burnt out, failing 'open,' and then subsequent damage occurred. This could be almost anything connected between HV and GND, and also anything connected to the other side of a component that might fail to a short circuit condition.

JViss: If the diode failed "Open", then the circuit wouldn't conduct electricity further. It just would have broken the circuit like a fuse.

There are cases where they "fry " and fuse "closed" -- but that's unusual, isn't it?

You are incorrect on that point. The protection diode is across the power rail, not in series with it. If it fails open, it's as if it was never there. If it conducts, it is short-circuiting the input power, drawing enough current to blow the protection fuse.

SG · Jun 3, 2018

JViss, but then if that protection fuse blows, doesn't the power simply get "killed"?

twalker H260 · Jun 3, 2018

On my radio the fuse is at the opposite end from the radio - a few inches from where it connects to the on/off breaker at the DC distribution panel. And as jackdaw indicated that connection at the radio end is a female bullet connector.

jviss · Jun 3, 2018

SG said:
JViss, but then if that protection fuse blows, doesn't the power simply get "killed"?

Updated: Not sure about your question. Can you please clarify?

Previous response:

No. If the protection fuse, which is outside the radio, in the wiring harness, blows, the circuit becomes open. No damage to the "power," though I'm not entirely sure what to what "power" you refer.

It's really quite simple, and works perfectly if you install the radio per the manufacturer's recommendation, which includes the external protection fuse. Correct polarity, the protection diode is reverse-biased and doesn't conduct; reverse polarity and the diode is forward biased, and conducts. The fuse blows so quickly that the approximately 0.7V forward bias voltage drop of the diode is not enough to do any damage.