1999 Yamaha 80hp Outboard Electrical Problem (Rectifier Overheating)

Question

I recently purchased a pontoon boat and on day #3 my motor died, I'm hoping to get some help from the community with correctly diagnosing and fixing the problem.

The motor - 1999 Yamaha 80hp four stroke (F80TLRX).

The problem - 30A fuse is blown, and when it's replaced the rectifier starts overheating (burning and smoking).

What happened - I was cruising along and started to increase throttle, but suddenly started losing power. With a minute or two the engine died, and I had no power to the tilt/trim motor (from either remote or engine side) or starter. One clue, or perhaps red herring, is that shortly before this occurred I tried turning on the fish finder. It didn't power up, which was odd, as it had worked previously before this cruise. Another clue/red herring, is that I found the electrical cable to the masthead light was under stress because of a broken seat cover.

Attempted solutions - My first step was checking the fuses, and the 30A fuse was blown. As mentioned the motor started smoking badly and emitting a burning smell when I replaced the fuse, which I confirmed was from the rectifier after removing some covers. I removed the in-line fuse connecting the fish finder, just in case that was causing a problem, and addressed the masthead light cable, but this didn't resolve anything. The battery is in good shape and the connections are clean and tight, and after inspection of the motor I can't find any loose/broken/chafed wires that might be the problem.

My first inclination is to just replace the rectifier, though if something is causing that to burn up I might just end up frying another one. Any suggestions for how to correctly identify and isolate the root cause would be greatly appreciated before I invest money in parts or a professional marine mechanic. (I may go with the latter in any case just to be on the safe side.)

Thanks in advance for any help offered.

Barry

Answer 1

First of all, a fuse is there to protect electrical parts from using or being exposed to too much amperage. When the circuit goes over this amperage, the fuse burns out. Since this happened to you, I'd suggest one of two things is going on.

• You have a short in that circuit. Since you stated you didn't see any chafing in the wires, this is not the problem. I'd suggest you go back over it with a fine tooth comb and ensure the circuit hasn't grounded somewhere.
• Your rectifier has gone bad and is causing the excess power drain. This I believe is your true issue. Do the double check on the circuit first. If it doesn't pan out, plan on replacing the rectifier.

I'm not sure if the rectifier is mounted to a ground, but you could possible remount it so that it isn't in contact with anything which becomes hot during the use of the motor. If you can put a small spacer in between so as to get the rectifier off of any hot parts, it may help it in the long run. This is only a preventive suggestion to prevent issues in the future. I know boat motors are very compact, so there may not be room to do this. It's just a thought.

Also, double check to ensure you are using the right fuse for the application. The fuse may have been an issue when you bought it, where the rectifier was using too much amperage in the first place and the previous owner "fixed it" by putting a higher amperage fuse in place. There is a reason why there are fuses, as described above. Use them wisely and your boat motor will be less likely to become a lump of molten metal.

Answer 2

The issue here was the voltage rectifier, it was damaged. I haven't had any problems since replacing it.

Answer 3

This is obviously a problem with Yamaha motors as I had the same thing happen to mine. When it died the first time I smelled the burning odor. I checked the battery and found the negative lead was really loose so I tightened it thinking that would cure the problem. Not to be. Had to troll back to launch area and take boat out without being able to tilt motor. Luckily it was a short gravel ramp. Manually raised to motor and drove it home. Took the cowl off the motor and checked for blown fuse. Sure enough a 30 A fuse was blown. I replaced that and the tilt and starter operated fine. Put the boat back in the water and only got about a quarter of a mile before I noticed the voltage dropping and it finally died. Same scenario this time but I did know to replace the fusee when I got back to the dock. I was able to crank the motor long enough to get it back on the trailer and have since had it in the shop for replacement of the voltage regulator. This was to the tune of $525. I'm keeping my fingers crossed for the next outing. I have heard through the grapevine that this is a problem with Yamaha motors. Mine is a 2002 model that I bought from an individual who had had it for some time. It had 300 hours on it when I bought it.