Furuno model 1720 radar unit.

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Dec 16, 2007
I keep blowing the 5 amp fuse on the unit when I turn the unit on. Any ideas out there?
A 10 amp fuse?? :)
I almost posted the same thing!!!!...haha. But somewhat seriously, do you have the owner's manual and is that the size of fuse it calls for. Seems a bit small.
I have the owner's manual in front of me and it calls for a FGMB 5 amp 125VAC fuse. I replaced it with a GMA 5 amp fuse and it blew immediately.
Okay....here comes my ignorance....but 125VAC??? I would think your radar would be 12 volt? I will admit of all the boats I have had, never had radar on them I am just surprised that it would be 125VAC powered.
Fuses are rated by max voltage they can be exposed to.

-- Edited by bluebyu on Sunday 11th of October 2009 04:49:58 AM
** Mr. ancora.** I am stating the obvious but your unit is drawing too much current someplace.* Are ALL your connections (Power from your 12V source, GROUND, connectors between CRT and Radome etc. clean and tight?* If not, clean connections and apply coating of dielectric grease.* Is there any corrosion under your Radome?* Take off the cover and inspect.
* If all the above meet specifications, either a call to Furuno tech support or service by an elelctronics guy may be in your future.
ancora wrote:

I have the owner's manual in front of me and it calls for a FGMB 5 amp 125VAC fuse. I replaced it with a GMA 5 amp fuse and it blew immediately.

The GMA is a fast acting fuse and it sounds like it is acting fast. It can't handle the inrush current. Find an FGMB

This week-end I disconnected the scanner from the display unit and the display unit went right on without blowing a fuse. I am thinking that the problem is in the scanner or the scanner harness. I have the schematics but they do not have a color code. Why should they? That would make the unit user friendly and we can't have that.
Ancora;*** * the scanner uses the most power which is why disconnecting it* stops the fuse from* blowing . It has been pointed out that the fuse you substituted is a fast blow wheras the specified fuse is slower blowing to carry through a start up surge.
A characteristic of most radar -especially Furuno - is that as the voltage drops the power supply draws more current.* Suggest* you check to see if the voltage was low whe the intial fuse blew.*Also recomment getting the proper fiuse before you conduct more testing.* Simply increasing fuse size may cause more damage if inded you do have a* circuit problem.*
Finally got my hands on some slow blow 5 amp fuses from Radio Shack with the same results.
They blew just as fast as the fast blow fuses.
How's the alignment of the motor drive?*Are the gears*still lubricated and does the antenna rotate freely?
I will get into the scanner this week-end and look for the problem.
Glad to see ya back Elnav!!!!
Opened up the scanner yesterday and everything looked good. The rotating member was free, as was the motor. Put in another fuse and energized the unit. The display unit went on properly so I hit transmit and the unit worked. Looked into the scanner and all looked well.
After about ten minutes the unit shut off by itself. Pulled the power plug from the display unit and the voltage checked out. Turned the unit on again and it started right up. I let it run on transmit for a half hour with no problems. Shut the unit down and fired it up and let it run for an hour with no shut-down. Don't know why, but it looks like I'm back in business.
The fact the unit shut itself off for no apparent reason sounds a little suspicious. We had a radio, an Icom 502, that started to freeze. Turning off the unit and turning it back on restored normal operation for 15 or 20 minutes, at which point it would freeze again.

Ran it on different batteries and eliminated all the other variables we could think of external to the radio and had the same results. So we removed it and gave it to the marine electronics shop we use to troubleshoot and fix it. He ran it for hours and it worked fine. Finally he left it on overnight and when he came in the next morning, it had frozen. No clue as to why. So he sent it to Icom (they have a factory service center in this area). They ran it for a week, froze it, heated it, shook it, and could not get it to fail. So they sent it back and we re-installed it. Worked fine for a month or so and then one day it froze again. Turned it of and back on and it worked fine and continued to do so for the next couple of cruises.

But the fact that the problem, whatever it was, was still there convinced me that we could no longer trust the unit. So we replaced it with a new Icom 504 which uses the same case so fits the same cutout, uses the same mount, etc.

The point being that if a piece of electronics develops a problem, even a mysterious, very intermittent one, and there does not seem to be any obvious fix, even if the unit starts working "reliably" again on its own, the chances are the problem is still lurking inside and will eventually happen again. Usually when you most need the unit.
Unfortuneatly, the cost of getting a Furuno tech to troubleshoot the unit far exceeds the value of the 26 year old unit. I"ll just have to take my chances.
Twenty-some year old electronics are going to be a bit of a crap shoot in any case.

Most commercial grade ICs are packaged in plastic.* Plastic has a different expansion coefficient versus temperature than the metal pins that are molded through the plastic.* With time (like 20 years or so) and enough temperature cycles, the metal and plastic can separate.* This leaves a miniscule opening for moisture to enter the device, and as you might guess, that's not a good thing.

Even if you can determine which part has failed, getting a replacement part can be difficult or impossible.* Plenty of two-decade-old parts are simply unavailable in the original package size and voltage range.

So Marin's post is spot-on.* Once the box is old enough to buy hard liquor and smoke, replacement is usually the best option.

BTW:* are you all aware that it's smoke that makes electronic devices work? *Cuz every time smoke comes out,*they stop*working.


Turned on the unit yesterday and it ran just fine. My problem now is with the Admiral. She wants to plug in the GPS to the Furuno. The Furuno book covers plugging in LORAN but nothing on GPS as it was not in use at the time. If the NMEA code is the same, is it possible?As usual, Furuno is no help.
Sure. You may have to select an older NMEA version than the Garmin provides by default. Usually under menu, options, NMEA or something like that. Just start with the default and work your way backwards if the first one doesn't work. Another problem is the cable to connect them... can you get one, or will you have to make one up? If the latter, you'll need the pin-outs and ins for the two pieces of equipment.
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